RESUMEN
BACKGROUND/OBJECTIVES: Expanding visceral adiposity is associated with increased inflammation and increased risk for developing obesity-related comorbidities. The goal of this study was to examine high fat diet (HFD)-induced differences in adipocyte size and cytokine/chemokine expression in visceral and subcutaneous adipose depots in obesity-prone (OP) and obesity-resistant (OR) rats. METHODS: OP and OR rats were fed either a low fat diet (LFD, 10% kilocalories from fat) or HFD (60% kilocalories from fat) for 7 weeks. Adipocyte size and the presence of crown-like structures in epididymal and inguinal adipose tissue were determined. A multiplex cytokine/chemokine panel was used to assess the expression of inflammatory markers in epididymal and inguinal adipose tissues. RESULTS: A higher percentage of large adipocytes (>5000 µm2) was detected in the epididymal and inguinal adipose tissues of OP rats and a higher percentage of small adipocytes (<4000 µm2) was detected in the epididymal and inguinal adipose tissues of OR rats. More crown-like structures were identified in epididymal adipose tissue of OP rats fed a LFD, compared to OR rats. Consumption of a HFD increased the number of crown-like structures in OR, but not OP rats. Epididymal expression of pro-inflammatory cytokines (IL-1ß and TNF-α) was higher in OP rats, compared to OR rats fed LFD. HFD consumption increased epididymal expression of GM-CSF, IL-1α, IL-1ß, IL-6, MIP-2 and TNF-α in OP and OR rats. Inguinal expression of pro-inflammatory cytokines (IL-1α, IL-1ß and TNF-α) was higher in OP rats, compared to OR rats. CONCLUSIONS: Overall, these data suggest that a higher susceptibility to developing obesity is characterized by large adipocytes and increased visceral adipose inflammation. Interestingly, in OR rats, the detrimental effects of HFD consumption on visceral adipose inflammation are evident with only small increases in weight and adiposity, suggesting that HFD also increases the risk for obesity-related comorbidities in OR rats.
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Adipocitos/metabolismo , Dieta Alta en Grasa/efectos adversos , Inflamación/metabolismo , Obesidad/metabolismo , Tejido Adiposo/citología , Tejido Adiposo/metabolismo , Animales , Biomarcadores/análisis , Biomarcadores/metabolismo , Células Cultivadas , Citocinas/análisis , Citocinas/metabolismo , Epidídimo/citología , Epidídimo/metabolismo , Masculino , RatasRESUMEN
Chronic infusion of angiotensin (Ang) II leads to the development of hypertension and enhances intrarenal Ang II content to levels greater than can be explained from the circulating concentrations of the peptide. We previously reported that renal angiotensinogen (Ao) mRNA is enhanced in Ang II-dependent hypertension and may contribute to augmented intrarenal Ang II levels, but the Ao protein levels were not significantly increased. Because a high-salt diet (H/S) has been shown to suppress renal expression of Ao mRNA, we examined the effects of chronic Ang II infusion on kidney and liver Ao mRNA and protein levels in male Sprague-Dawley rats (n=12) maintained on an 8% salt diet. Ang II was administered via osmotic minipumps (40 ng/min) to 1 group (n=6) while the remaining rats were sham-operated. A H/S diet alone did not alter systolic blood pressure in sham animals (109+/-6 mm Hg at day 12); however, Ang II infusions to the H/S rats significantly increased systolic blood pressure (167+/-7 at day 12) and intrarenal Ang II content (459+/-107 fmol/g versus 270+/-42) despite a marked suppression of plasma renin activity (0.9+/-0.2 ng Ang I. mL(-1). h(-1) versus 2.8+/-1.3). Ang II infusions significantly increased kidney Ao mRNA compared with the H/S diet alone by 1.9+/-0.1-fold. Western blot analysis of kidney protein extracts showed that the Ang II-infused rats had increased kidney Ao protein levels compared with the H/S diet alone (1.9+/-0.1-fold). Liver Ao mRNA and protein and plasma Ao protein were also significantly increased by Ang II infusions. These data demonstrate the effects of Ang II infusion to stimulate Ao mRNA and protein. Thus, the augmented intrarenal Ang II in Ang II-dependent hypertension may result, in part, by a positive amplification mechanism to activate renal expression of AO:
Asunto(s)
Angiotensina II/sangre , Angiotensinas/sangre , Hipertensión/sangre , Angiotensina II/metabolismo , Angiotensinas/biosíntesis , Angiotensinas/genética , Animales , Presión Sanguínea , Western Blotting , Peso Corporal , Dieta , Modelos Animales de Enfermedad , Hipertensión/inducido químicamente , Hipertensión/metabolismo , Riñón/metabolismo , Hígado/metabolismo , Masculino , ARN Mensajero/biosíntesis , Ratas , Ratas Sprague-Dawley , Renina/sangre , Sodio en la DietaRESUMEN
Congenital abnormalities of the kidney and urinary tract are a common cause of end-stage renal disease in children. Host and environment factors are implicated in the pathogenesis of aberrant renal development. However, direct evidence linking gene-environment interactions with congenital renal disease is lacking. We report an animal model of renal dysgenesis that is dependent on a defined genetic defect and specific embryonic stressor. Specifically, mice that are deficient in the bradykinin type 2 receptor gene (B(2)) and salt loaded during embryogenesis acquire an aberrant kidney phenotype and die shortly after birth. In contrast, B(2) mutant mice maintained on normal sodium intake or salt-loaded wild-type mice do not develop kidney abnormalities. The kidney abnormality is evident histologically on embryonic day 16, shortly after the onset of metanephric B(2) gene expression, and consists of distorted renal architecture, foci of tubular dysgenesis, and cyst formation. The dysplastic tubules are of distal nephron origin [Dolichos biflorus agglutinin (DBA)- and aquaporin-2 (AQP2) positive, and angiotensinogen negative]. Neonatal antihypertensive therapy fails to ameliorate the renal abnormalities, arguing against the possibility that the nephropathy is a consequence of early hypertension. Moreover, the nephropathy is intrinsic to the embryo, because B(2) homozygous offspring from heterozygous parents exhibit the same renal phenotype as offspring from homozygous null parents. Further characterization of the renal phenotype revealed an important genetic background effect since the penetrance of the congenital nephropathy is increased substantially upon backcrossing of 129/BL6 B(2) mutants to a uniform C57BL/6J. We conclude that the type 2 bradykinin receptor is required for the maintenance of metanephric structure and epithelial integrity in the presence of fetal stress. This study provides a "proof-of-principle" that defined gene-environment interactions are a cause of congenital renal disease.
Asunto(s)
Riñón/anomalías , Receptores de Bradiquinina/genética , Angiotensinógeno/análisis , Animales , Animales Recién Nacidos , Antihipertensivos/farmacología , Acuaporina 2 , Acuaporina 6 , Acuaporinas/análisis , Dieta , Desarrollo Embrionario y Fetal/genética , Femenino , Regulación del Desarrollo de la Expresión Génica , Edad Gestacional , Hidralazina/farmacología , Inmunohistoquímica , Riñón/efectos de los fármacos , Riñón/embriología , Túbulos Renales Proximales/anomalías , Túbulos Renales Proximales/química , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos , Ratones Mutantes , Ratones Transgénicos , Embarazo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Receptor de Bradiquinina B2 , Renina/análisis , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Cloruro de Sodio/administración & dosificación , Factores de TiempoRESUMEN
The dynamic activity of afferent arteriolar diameter (AAD) and blood flow (AABF) responses to a rapid step increase in renal arterial pressure (100-148 mmHg) was examined in the kidneys of normal Sprague-Dawley rats (n = 11) before [tubuloglomerular feedback (TGF)-intact] and after interruption of distal tubular flow (TGF-independent). Utilizing the in vitro blood-perfused juxtamedullary nephron preparation, fluctuations in AAD and erythrocyte velocity were sampled by using analog-to-digital computerized conversion, video microscopy, image shearing, and fast-frame, slow-frame techniques. These assessments enabled dynamic characterization of the autonomous actions and collective interactions between the myogenic and TGF mechanisms at the level of the afferent arteriole. The TGF-intact and TGF-independent systems exhibited common initial (0-24 vs. 0-13 s, respectively) response slope kinetics (-0.53 vs. -0.47% DeltaAAD/s; respectively) yet different maximum vasoconstrictive magnitude (-11.28 +/- 0.1 vs. -7. 02 +/- 0.9% DeltaAAD; P < 0.05, respectively). The initial AABF responses similarly exhibited similar kinetics but differing magnitudes. In contrast, during the sustained pressure input (13-97 s), the maximum vasoconstrictor magnitude (-7.02 +/- 0.9% DeltaAAD) and kinetics (-0.01% DeltaAAD/s) of the TGF-independent system were markedly blunted whereas the TGF-intact system exhibited continued vasoconstriction with slower kinetics (-0.20% DeltaAAD/s) until a steady-state plateau was reached (-25.9 +/- 0.4% DeltaAAD). Thus the TGF mechanism plays a role in both direct mediation of vasoconstriction and in modulation of the myogenic response.
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Arteriolas/fisiología , Glomérulos Renales/irrigación sanguínea , Túbulos Renales/irrigación sanguínea , Circulación Renal/fisiología , Animales , Velocidad del Flujo Sanguíneo/fisiología , Presión Sanguínea/fisiología , Retroalimentación/fisiología , Técnicas In Vitro , Glomérulos Renales/fisiología , Túbulos Renales/fisiología , Masculino , Modelos Cardiovasculares , Nefronas/irrigación sanguínea , Nefronas/fisiología , Ratas , Ratas Sprague-Dawley , Análisis de Regresión , Grado de Desobstrucción Vascular/fisiología , Vasoconstricción/fisiologíaRESUMEN
Cardiovascular disease is the leading cause of death in women and claims the lives of more than half a million women every year. Hypertension is one of the most prevalent and powerful contributors to atherosclerotic cardiovascular disease. Hypertension affects more men than women until 55 years of age, but after age 55, the percentage of women is higher. Estrogen deficiency has been linked to the rapid increase in cardiovascular disease in women who have undergone natural or surgical menopause. Hormone replacement therapy (HRT) has been shown to decrease the incidence of cardiovascular disease and, in some studies, to reduce blood pressure in postmenopausal women. However, little information is available on the effects of HRT on blood pressure in hypertensive postmenopausal patients. The cardioprotective effects of estrogens are not completely understood but may involve direct effects on blood vessels through modulation of endogenous vasoconstrictors and vasodilators and through reductions in serum lipoprotein and cholesterol levels. Experimental evidence suggests that estrogen increases the biological actions of nitric oxide and decreases the actions of angiotensin. After menopause, loss of the vascular protective effects of estrogens may unmask a population of women particularly prone to hypertension who would be at higher risk for cardiovascular disease.
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Terapia de Reemplazo de Hormonas , Hipertensión/tratamiento farmacológico , Posmenopausia/fisiología , Factores de Edad , Animales , Estrógenos/fisiología , Estrógenos/uso terapéutico , Femenino , Humanos , Hipertensión/fisiopatología , Masculino , Persona de Mediana Edad , Óxido Nítrico/fisiología , Posmenopausia/efectos de los fármacos , Sistema Renina-Angiotensina/fisiología , Factores SexualesRESUMEN
In several models of angiotensin II (ANG II) dependent hypertension, intrarenal ANG II levels increase to a much greater extent than the circulating levels even though the renal renin levels are decreased. The 2-kidney-1-clip (2K1C) Goldblatt rat model is particularly intriguing because hypertension develops in the presence of an intact kidney which would be expected to maintain sodium balance and protect against hypertension. Although the non-clipped kidney becomes renin depleted, it exhibits enhanced microvascular reactivity and increased tubular fractional sodium reabsorption. The non-clipped kidney ANG II content is either elevated or unchanged and proximal tubular fluid ANG II concentrations are not suppressed compared to the nanomolar concentrations found in normal rats. These results suggest that intrarenal ANG II content can be regulated independently of renal renin content. A similar hypertensive process occurs in rats infused chronically with low doses of ANG II. Renal ANG II content increases over 14 days to a greater extent than the circulating concentrations. Functionally, ANG II infused rats demonstrate reduced sodium excretion and marked suppression of pressure natriuresis. These ANG II dependent influences on kidney function contribute to the maintenance of hypertension. Renal augmentation of ANG II, hypertension, and suppressed sodium excretion are blocked by AT1 receptor blockers. To study the mechanisms responsible for intrarenal ANG II augmentation, we infused a different form of ANG II (Val5 ANG II), that can be separated from endogenous ANG II by HPLC. These results indicated that the increased renal ANG II content was due to accumulation of circulating ANG II in addition to continued production of endogenous ANG II. The renal accumulation of Val5-ANG II was markedly reduced by concomitant treatment with the AT1 receptor blocker, losartan. In addition, we found an unchanged overall ANG II-AT1 receptor protein which probably contributes to the maintained ANG II dependent influences. Collectively, the data support the concept that there is internalization of ANG II through an AT1 receptor mediated process and that some of the internalized ANG II is protected from degradation. The augmented intrarenal ANG II coupled with sustained levels of AT1 receptors contribute to the continued ANG II dependent suppression of renal function and sodium excretion thereby maintaining the hypertension.
Asunto(s)
Angiotensina II/análogos & derivados , Angiotensina II/metabolismo , Hipertensión/etiología , Riñón/metabolismo , Animales , Endosomas/metabolismo , Hipertensión/inducido químicamente , Hipertensión/metabolismo , Membranas Intracelulares/metabolismo , Receptores de Angiotensina/metabolismo , Obstrucción de la Arteria Renal/fisiopatologíaRESUMEN
Because of the importance of the renin-angiotensin system in the pathophysiology of hypertension and in mediating associated alterations in renal function, angiotensin II (Ang II) AT1 receptor blockers provide a direct means of protecting against influences of excessive Ang II levels. The kidney is an important site of action of Ang II AT1 receptor blockers because intrarenal Ang II not only vasoconstricts the renal vasculature but also reduces sodium excretion and suppresses the pressure natriuresis relationship. Even in normal conditions, intrarenal Ang II content is greater than can be explained on the basis of circulating Ang II and is compartmentalized with proximal tubule concentrations of Ang I and Ang II being several times higher than plasma concentrations. The localization of angiotensinogen in proximal tubule cells further supports the concept that the proximal tubule secretes Ang II or precursors of Ang II into the tubular fluid to activate luminal Ang II receptors. Recent immunohistochemical studies have demonstrated an abundance of AT1 receptors on the luminal surface of proximal and distal tubule cells as well as on vascular smooth muscle cells of afferent and efferent arterioles and on glomerular mesangial cells. Activation of luminal AT1 receptors stimulates the sodium hydrogen exchanger and increases reabsorption rate. The prominence of AT1 receptors in vascular and epithelial tissues in the kidney provides the basis for the powerful effects of AT1 receptor blockers on renal function especially in hypertensive conditions. In the two-kidney, one-clip (2K1C) Goldblatt hypertensive rat model, the nonclipped kidney is renin depleted but the intrarenal Ang II levels are not suppressed and Ang II concentrations in proximal tubular fluid remain high (10(-8) mol/L). AT1 receptor blockers such as candesartan have been shown to cause significant increases in glomerular filtration rate, renal blood flow and proportionately much greater increases in sodium excretion and fractional sodium excretion. Ang II blockade also markedly increases the slope of the pressure natriuresis relationship. The collective actions of Ang II blockers on tubular transport and renal hemodynamics provide long-term effects to regulate sodium balance, which contributes to the long-term control of hypertension.
Asunto(s)
Antagonistas de Receptores de Angiotensina , Riñón/química , Riñón/fisiología , Receptores de Angiotensina/fisiología , Circulación Renal/fisiología , Animales , Antihipertensivos/farmacología , Bencimidazoles/farmacología , Compuestos de Bifenilo , Hipertensión Renal/tratamiento farmacológico , Hipertensión Renal/fisiopatología , Receptor de Angiotensina Tipo 1 , Receptor de Angiotensina Tipo 2 , Tetrazoles/farmacologíaRESUMEN
Kinins have been implicated in the hemodynamic adaptation to postnatal life. The present study examined the impact of bradykinin B(2) receptor (B(2)R) gene disruption on the postnatal changes in blood pressure (BP) and the susceptibility to early onset salt-sensitive hypertension in mice. B(2)R null (-/-) and wild-type (+/+) mice were fed normal (NS, 1% NaCl) or high (HS, 5% NaCl) salt diets during pregnancy. After birth, the pups remained with their mothers until they were weaned and were subsequently continued on the respective maternal salt intake until 4 months of age. The age-related changes at 3 and 4 months in tail-cuff BP and anesthetized mean arterial pressure at 4 months were not different in NS/B(2)R(-/-) and NS/B(2)R(+/+) mice. However, there was a mild increase in BP in NS/B(2)R(-/-) at 2 months versus NS/B(2)R(+/+). In contrast, HS/B(2)R(-/-) mice manifested early onset and persistent elevations of tail-cuff BP (P<0.05) at 2, 3, and 4 months versus other groups. MAP was also higher in HS/B(2)R(-/-) than HS/B(2)R(+/+), NS/B(2)R(-/-), and NS/B(2)R(+/+) (91+/-3 versus 75+/-5, 74+/-2, and 70+/-2 mm Hg, respectively; P<0.05). Kidney renin and angiotensin type 1 receptor mRNA levels were not different. Additional studies showed that a delay in the initiation of HS until after birth was accompanied by later development of hypertension, although postnatal discontinuation of HS resulted in a gradual return of BP to normal values by 4 months of age. The results demonstrate that (1) kinins protect the developing animal from salt-sensitive hypertension, (2) lack of B(2)R from early development does not alter the maturation of BP under conditions of normal sodium intake, and (3) exposure to a HS diet during fetal life is not sufficient in itself to induce long-term hypertension in either wild-type or B(2)R null mice.
Asunto(s)
Presión Sanguínea/fisiología , Hipertensión/etiología , Sistema Calicreína-Quinina/fisiología , Receptores de Bradiquinina/genética , Sistema Renina-Angiotensina/fisiología , Cloruro de Sodio Dietético/farmacología , Factores de Edad , Angiotensina II/análisis , Angiotensina II/sangre , Animales , Animales Recién Nacidos , Presión Sanguínea/genética , Northern Blotting , Peso Corporal , Interpretación Estadística de Datos , Femenino , Hipertensión/genética , Hipertensión/fisiopatología , Riñón/química , Masculino , Ratones , Ratones Noqueados , Embarazo , ARN Mensajero/análisis , Radioinmunoensayo , Receptores de Angiotensina/genética , Sistema Renina-Angiotensina/genética , Cloruro de Sodio Dietético/administración & dosificaciónRESUMEN
The intrarenal renin-angiotensin system plays a critical role in the paracrine regulation of renal function and the pathophysiology of hypertension. Angiotensin II (AngII) is formed intrarenally from systemically delivered angiotensin I (AngI) and intrarenally formed AngI. Intrarenal AngII content, which is greater than can be explained by the circulating AngII concentrations, is compartmentalized such that proximal tubule concentrations of AngI and AngII greatly exceed plasma concentrations. Proximal tubule cells are thought to secrete AngII or precursors of AngII into the tubular fluid to activate luminal AngII receptors. Recent immunohistochemical studies have demonstrated an abundance of AT1 receptors on the luminal surface of proximal and distal tubule cells and on afferent and efferent arteriolar vascular smooth muscle cells and mesangial cells of glomeruli. Activation of luminal AT1 receptors stimulates tubular sodium reabsorption rate. To evaluate the direct effects of AT1 receptor blockade on renal function in AngII-dependent hypertension, experiments were performed on two-kidney, one-clip (2K1C) Goldblatt hypertensive rats. Although the nonclipped kidney is renin-depleted, the intrarenal AngII levels are not suppressed, and AngII concentrations in proximal tubular fluid remain high (10(-8) M). Candesartan was administered into the renal artery of nonclipped kidneys to avoid the confounding consequences of decreases in arterial pressure. Blockade of intrarenal AT1 receptors elicited significant increases in GFR, renal blood flow, sodium excretion, and fractional sodium excretion, suggesting synergistic actions on tubular transport and vascular smooth muscle cells.
Asunto(s)
Angiotensina II/fisiología , Antagonistas de Receptores de Angiotensina , Antihipertensivos/farmacología , Bencimidazoles/farmacología , Hipertensión Renovascular/fisiopatología , Riñón/metabolismo , Receptores de Angiotensina/fisiología , Tetrazoles/farmacología , Angiotensina I/análisis , Angiotensina I/fisiología , Angiotensina II/análisis , Animales , Compuestos de Bifenilo , Tasa de Filtración Glomerular , Natriuresis/efectos de los fármacos , Natriuresis/fisiología , Ratas , Circulación Renal/efectos de los fármacos , Sistema Renina-Angiotensina/fisiologíaRESUMEN
Chronic elevations of circulating angiotensin II (Ang II) cause sustained hypertension and enhanced accumulation of intrarenal Ang II by an AT1 receptor-dependent process. The present study tested the hypothesis that chronic elevations in circulating Ang II regulate AT1 mRNA and protein expression in a tissue-specific manner. Sprague-Dawley rats were infused with Ang II (80 ng/min) or vehicle subcutaneously for 13 days via osmotic minipump. On day 12, systolic blood pressure averaged 186+/-12 mm Hg in Ang II-infused rats compared with rats given vehicle (121+/-2 mm Hg). Plasma renin activity was markedly suppressed in the Ang II-infused rats compared with vehicle-infused rats (0.1+/-0.01 versus 4.9+/-0.9 ng of Ang I. mL-1. h-1; P<0.05). Semiquantitative reverse transcription polymerase chain reaction using rat AT1A- and glyceraldehyde-3-phosphate-dehydrogenase (GAPDH)-specific primers was followed by Southern blot hybridization using specific radiolabeled cDNA or oligonucleotide probes. The results showed that the ratios of AT1A/GAPDH mRNA in the kidney (0.19+/-0.05 versus 0. 26+/-0.03) and liver (2.8+/-0.9 versus 3.0+/-0.5) were comparable in Ang II- and vehicle-infused rats. In contrast, AT1A/GAPDH mRNA levels were increased in the adrenal glands of Ang II-infused rats (0.49+/-0.04 versus 0.36+/-0.02; P<0.05). Western blot analysis showed that AT1 protein levels in the kidney and liver were also similar in the two groups. Therefore, these results indicate that renal and liver AT1 receptor gene expression is maintained in Ang II-induced hypertension. The failure to downregulate AT1 receptor mRNA and protein levels thus allows the sustained effects of chronic elevations in Ang II to elicit progressive increases in arterial pressure.
Asunto(s)
Angiotensina II/farmacología , Regulación de la Expresión Génica/fisiología , Hipertensión/metabolismo , Riñón/metabolismo , Hígado/metabolismo , Receptores de Angiotensina/genética , Transcripción Genética/fisiología , Angiotensina I/administración & dosificación , Angiotensina I/farmacología , Angiotensina II/administración & dosificación , Angiotensina II/sangre , Animales , Presión Sanguínea/efectos de los fármacos , Regulación de la Expresión Génica/efectos de los fármacos , Hipertensión/inducido químicamente , Hipertensión/fisiopatología , Infusiones Intravenosas , Masculino , ARN Mensajero/genética , Ratas , Ratas Sprague-Dawley , Receptor de Angiotensina Tipo 1 , Receptor de Angiotensina Tipo 2 , Valores de Referencia , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transcripción Genética/efectos de los fármacosRESUMEN
Although the presence of angiotensin II (AngII) receptors on the luminal membranes of proximal tubule cells has been recognized for many years, recent immunohistochemical studies using polyclonal and monoclonal antibodies to the AngII type 1 (AT1) receptor have demonstrated an abundance of the AT1 receptor not only on the luminal surface of proximal tubule cells but also on the luminal surfaces of distal nephron segments. An important role for these receptors in the regulation of tubular transport mechanisms was indicated by the recent findings of remarkably high proximal intratubular concentrations of AngII (in the range of 10(-9) to 10(-8) M). The high intratubular concentrations of AngII, as well as angiotensin I and angiotensinogen, are much greater than can be explained on the basis of delivery via glomerular filtration. When coupled with the findings demonstrating the presence of angiotensinogen and angiotensinogen mRNA in proximal tubule cells, the data indicate that AngII or precursors of AngII are secreted directly into the proximal tubule lumen by the epithelial cells. Although the mechanisms responsible for the regulation of intratubular AngII concentrations remain to be determined, micropuncture studies have provided direct evidence that activation of intraluminal AT1 receptors by AngII exerts a substantial stimulatory influence on sodium and bicarbonate transport by both proximal and distal tubules. Collectively, these data provide support for the hypothesis that activation of luminal AT1 receptors by AngII present in the tubular fluid contributes importantly to regulation of the tubular reabsorption rate.
Asunto(s)
Angiotensina II/análisis , Túbulos Renales Distales/metabolismo , Túbulos Renales Proximales/metabolismo , Receptores de Angiotensina/análisis , Angiotensina II/fisiología , Angiotensinógeno/análisis , Animales , Transporte Biológico , Biopsia con Aguja , Líquidos Corporales/metabolismo , Membrana Celular/metabolismo , Células Cultivadas , Células Epiteliales/metabolismo , Receptor de Angiotensina Tipo 1 , Receptor de Angiotensina Tipo 2 , Receptores de Angiotensina/fisiologíaRESUMEN
Molecular and functional studies have suggested that AT1 receptors are present in most nephron segments, yet direct demonstration of AT1 at these sites is lacking. The present study was performed to determine the intrarenal localization of the AT1 receptor utilizing a monoclonal anti-peptide (amino acid residues 8-17) antibody (6313/G2) in adult male Sprague-Dawley rats. Western blot analysis of kidney protein extracts showed a predominant 41-kDa immunoreactive band corresponding to the molecular weight of the deduced cDNA sequence. To determine optimal fixation conditions, kidney tissues were immersion fixed in Bouin's solution, 10% buffered Formalin, or 4% paraformaldehyde. Specificity of immunostaining was documented by preadsorption of the antibody with the immunogenic peptide sequence. Prominent AT1 immunostaining was visualized in the proximal tubule brush-border and basolateral membranes. In addition, distal tubules, cortical and medullary collecting ducts, and the renal arterial vasculature exhibited specific immunoreactivity. Glomerular staining for AT1 was observed in mesangial cells and podocytes. Macula densa cells stained positively. Similar localization of the AT1 receptor was obtained using the three tissue fixation methods, although the intensity of vascular and glomerular staining was highest in Bouin-fixed tissues. The present study demonstrates that the AT1 receptor is more widely distributed along the nephron than previously described and includes renal vascular smooth muscle and proximal and distal epithelial sites.
Asunto(s)
Riñón/citología , Receptores de Angiotensina/análisis , Secuencia de Aminoácidos , Animales , Anticuerpos Monoclonales , Western Blotting , ADN Complementario , Riñón/metabolismo , Corteza Renal/citología , Médula Renal/citología , Túbulos Renales Colectores/citología , Túbulos Renales Distales/citología , Túbulos Renales Proximales/citología , Masculino , Fragmentos de Péptidos/química , Fragmentos de Péptidos/inmunología , Ratas , Ratas Sprague-Dawley , Receptor de Angiotensina Tipo 1 , Receptor de Angiotensina Tipo 2 , Receptores de Angiotensina/biosíntesisRESUMEN
Previous studies have demonstrated the critical role of the afferent arteriole in autoregulation of nephron blood flow in response to changes in perfusion pressure. The present study focused on the responses of postglomerular vascular segments to alterations in renal arterial pressure. Afferent arterioles, efferent arterioles and outer medullary descending vasa recta of juxtamedullary nephrons were visualized using the in vitro blood-perfused juxtamedullary nephron technique. Simultaneous measurements of inside vessel diameter and centerline erythrocyte velocity were made in order to determine single vessel blood flow. Blood flow measured in afferent arterioles (N = 13) displayed efficient autoregulation of blood flow and afferent arterioles responded actively with decreases in arteriolar diameter during stepwise elevations of renal perfusion pressure from 100 to 150 mm Hg. Similarly, blood flow measured at efferent arterioles (N = 9) exhibited autoregulation during increases in renal perfusion pressure. However, efferent arteriolar diameters were not altered during increases in perfusion pressure. During superfusion with the calcium channel blocker, diltiazem (10 microM), which primarily dilates afferent arterioles, efferent arteriolar blood flow (N = 7) increased and responded to changes in perfusion pressure. Nevertheless, efferent arteriolar diameter remained unchanged and did not respond to increases in perfusion pressure. Outer medullary descending vasa recta (N = 7) diameter, centerline erythrocyte velocity and calculated blood flow were also not significantly altered following stepwise increases in pressure to 125 and 150 mm Hg. These data demonstrate effective autoregulation of postglomerular blood flow, measured at efferent arterioles and at outer medullary descending vasa recta, over a perfusion pressure range of 100 to 150 mm Hg. There was no dissociation of arteriolar and outer medullary descending vasa recta blood flow responses to increases in renal perfusion pressure indicative of efficient autoregulation in both cortical and medullary postglomerular circulations of the rat.
Asunto(s)
Homeostasis/fisiología , Corteza Renal/irrigación sanguínea , Médula Renal/irrigación sanguínea , Animales , Arteriolas/fisiología , Presión Sanguínea , Masculino , Microcirculación/fisiología , Ratas , Ratas Sprague-DawleyRESUMEN
There has been an explosive growth of interest in the multiple interacting paracrine systems that influence renal microvascular function. This review first discusses the membrane activation mechanisms for renal vascular control. Evidence is provided that there are differential activating mechanisms regulating pre- and postglomerular arteriolar vascular smooth muscle cells. The next section deals with the critical role of the endothelium in the control of renal vascular function and covers the recent findings related to the role of nitric oxide and other endothelial-derived factors. This section is followed by an analysis of the roles of vasoactive paracrine systems that have their origin from adjoining tubular structures. The interplay of signals between the epithelial cells and the vascular network to provide feedback regulation of renal hemodynamics is developed. Because of their well-recognized contributions to the regulation of renal microvascular function, three major paracrine systems are discussed in separate sections. Recent findings related to the role of intrarenally formed angiotensin II and the prominence of the AT1 receptors are described. The possible contribution of purinergic compounds is then discussed. Recognition of the emerging role of extracellular ATP operating via P2 receptors as well as the more recognized functions of the P1 receptors provides fertile ground for further studies. In the next section, the family of vasoactive arachidonic acid metabolites is described. Possibilities for a myriad of interacting functions operating both directly on vascular smooth muscle cells and indirectly via influences on endothelial and epithelial cells are discussed. Particular attention is given to the more recent developments related to hemodynamic actions of the cytochrome P-450 metabolites. The final section discusses unique mechanisms that may be responsible for differential regulation of medullary blood flow by locally formed paracrine agents. Several sections provide perspectives on the complex interactions among the multiple mechanisms responsible for paracrine regulation of the renal microcirculation. This plurality of regulatory interactions highlights the need for experimental strategies that include integrative approaches that allow manifestation of indirect as well as direct influences of these paracrine systems on renal microvascular function.
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Hormonas/fisiología , Circulación Renal/fisiología , Animales , Ácido Araquidónico/metabolismo , Endotelio Vascular/fisiología , Humanos , Microcirculación/fisiología , Purinas/metabolismo , Sistema Renina-Angiotensina/fisiología , Transducción de SeñalRESUMEN
1. Experiments were designed to evaluate the hypothesis that cyclo-oxygenase products modulate the influence of angiotensin II (AII) on the renal juxtamedullary microvasculature of enalaprilat-treated rats. 2. The in vitro blood-perfused juxtamedullary nephron technique was utilized to provide access to afferent arterioles, efferent arterioles and descending vasa recta located in the outer stripe of the outer medulla. 3. Baseline afferent arteriolar diameter was 20.8 +/- 1.9 microns in kidneys subjected to cyclo-oxygenase blockade (1 mumol/L piroxicam), a value significantly lower than that observed in untreated kidneys (26.1 +/- 1.0 microns). Baseline diameters of efferent arterioles and outer medullary descending vasa recta did not differ between untreated and piroxicam-treated groups. 4. Topical application of 1 nmol/L AII reduced blood flow through outer medullary descending vasa recta by 22 +/- 6% in untreated kidneys and by 24 +/- 7% in piroxicam-treated kidneys. 5. In untreated kidneys, AII (0.01-100 nmol/L) produced concentration-dependent afferent and efferent arteriolar constrictor responses of similar magnitudes. Neither afferent nor efferent arteriolar AII responsiveness was significantly altered in piroxicam-treated kidneys, although afferent responses exceeded efferent responses at AII concentrations > or = 10 nmol/L. 6. We conclude that endogenous cyclo-oxygenase products exert a vasodilator influence on juxtamedullary afferent arterioles under baseline conditions. Although cyclo-oxygenase inhibition had little effect on juxtamedullary microvascular responses to AII, the response to high AII concentrations may be modulated by cyclo-oxygenase products in a manner which delicately alters the relative influence of the peptide on pre- vs postglomerular resistances.
Asunto(s)
Angiotensina II/farmacología , Inhibidores de la Ciclooxigenasa/farmacología , Aparato Yuxtaglomerular/efectos de los fármacos , Circulación Renal/efectos de los fármacos , Vasoconstrictores/farmacología , Inhibidores de la Enzima Convertidora de Angiotensina/farmacología , Animales , Arteriolas/efectos de los fármacos , Arteriolas/fisiología , Enalapril/farmacología , Eritrocitos/citología , Eritrocitos/efectos de los fármacos , Tasa de Filtración Glomerular/efectos de los fármacos , Tasa de Filtración Glomerular/fisiología , Técnicas In Vitro , Aparato Yuxtaglomerular/irrigación sanguínea , Aparato Yuxtaglomerular/fisiología , Médula Renal/irrigación sanguínea , Médula Renal/efectos de los fármacos , Médula Renal/fisiología , Masculino , Nefronas , Piroxicam/efectos adversos , Ratas , Ratas Sprague-Dawley , Circulación Renal/fisiología , Estadística como AsuntoRESUMEN
Utilizing the in vitro blood-perfused juxtamedullary nephron preparation, we examined the effects of alterations in renal arterial pressure on afferent arteriolar blood flow. With video microscopy and cross-correlation techniques, arteriolar inside diameters and centerline erythrocyte velocity were measured to estimate single afferent arteriolar blood flow. In response to random changes in perfusion pressure, afferent arteriolar diameter (n = 8) varied inversely (-0.53 +/- 0.02%/mmHg), and erythrocyte velocity was directly related (1.4 +/- 0.1%/mmHg). Above 95 mmHg, the slope of the relationship between perfusion pressure and afferent arteriolar blood flow did not differ from zero (0.081 +/- 0.053%/mmHg), suggesting efficient autoregulation. When the tubuloglomerular feedback pathway was interrupted by the addition of furosemide (n = 9) or papillectomy (n = 7), there was attenuation of pressure-induced afferent arteriolar constriction, with impairment in blood flow autoregulation (0.60 +/- 0.05%/mmHg). Superfusion with diltiazem abolished autoregulatory responses in afferent arteriolar diameter and blood flow (1.5 +/- 0.2%/mmHg). These data demonstrate the autoregulation of blood flow of individual afferent arterioles in juxtamedullary nephrons and suggest that both tubuloglomerular feedback-dependent and -independent mechanisms are required for autoregulatory responses.
Asunto(s)
Arteriolas/fisiología , Velocidad del Flujo Sanguíneo , Presión Sanguínea , Aparato Yuxtaglomerular/irrigación sanguínea , Médula Renal/irrigación sanguínea , Nefronas/irrigación sanguínea , Circulación Renal , Animales , Retroalimentación , Homeostasis , Masculino , Músculo Liso Vascular/fisiología , Ratas , Ratas Sprague-Dawley , Flujo Sanguíneo RegionalRESUMEN
Experiments were performed to determine the site of arginine vasopressin (AVP)-induced vascular resistance adjustments that result in decreases in papillary blood flow. Simultaneous measurements of luminal diameter and centerline erythrocyte velocity allowed estimation of single-vessel blood flow in in vitro blood-perfused juxtamedullary nephrons. AVP (0.1-1,000 pM) caused concentration-dependent reductions in outer medullary descending vasa recta (OMDVR) blood flow (10 pM) without altering OMDVR diameter. Afferent arteriolar diameter was significantly decreased by 1 pM AVP, whereas arcuate artery diameter was decreased by 100 pM AVP. Increasing the concentration of AVP to 1,000 pM resulted in significant reductions of vessel diameter in interlobular arteries, distal afferent arterioles, and efferent arterioles. The effects of AVP to decrease afferent arteriolar diameter and blood flow were blocked in the presence of V1 receptor antagonist. These data indicate that afferent arterioles exhibit the greatest sensitivity to the vasoconstrictor effects of AVP, whereas OMDVR appear insensitive. We conclude that the change in OMDVR blood flow produced by AVP is not due to a direct effect of the peptide on this vascular segment but to its effect on upstream vessels.
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Arginina Vasopresina/farmacología , Médula Renal/irrigación sanguínea , Circulación Renal/efectos de los fármacos , Animales , Eritrocitos/fisiología , Masculino , Microcirculación/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Resistencia Vascular/efectos de los fármacosRESUMEN
Experiments utilized the open cremaster preparation to test the hypothesis that atrial natriuretic peptide (ANP)-induced volume changes result from microvascular resistance alterations. Atrial natriuretic peptide (25, 100, and 500 ng/kg/min, IV) or vehicle was infused into anesthetized rats. At the two highest ANP infusion rates, mean arterial pressure was significantly reduced from 104 +/- 3 (control) to 87 +/- 2 and 77 +/- 2 mmHg, respectively. Hematocrit was 41.0 +/- 0.8 and 45.6 +/- 0.9% (p < 0.05) at the end of vehicle and ANP infusions, respectively. Despite these effects of ANP, there were no significant arteriolar or venular diameter alterations. Thirty microM nitroprusside significantly dilated all vessel segments except large venules. These observations suggest that resistance alterations in the skeletal muscle microvasculature are not the cause of ANP-induced fluid movement.
Asunto(s)
Factor Natriurético Atrial/farmacología , Músculos/efectos de los fármacos , Resistencia Vascular/efectos de los fármacos , Animales , Hematócrito , Hemodinámica/efectos de los fármacos , Masculino , Microcirculación/efectos de los fármacos , Músculos/irrigación sanguínea , Ratas , Ratas Sprague-DawleyRESUMEN
The present study was designed to examine acute (2 h) and chronic (5 day) effects of pathophysiological elevations of plasma atrial natriuretic factor (ANF) in conscious normotensive rats. Acute infusion of ANF (100 ng.kg-1.min-1; n = 15) resulted in a decrease in mean arterial pressure (MAP) of 5 +/- 3 mmHg, which was associated with a 23 +/- 4% decrease in cardiac output (CO) and a 27 +/- 6% increase in total peripheral resistance (TPR). Hematocrit increased from 41.9 +/- 0.7 to 46.0 +/- 0.6%, which is suggestive of vascular volume contraction. Chronic infusion of ANF (n = 9) produced a significant fall in MAP from a control value of 114 +/- 2 to 100 +/- 3 and 99 +/- 2 mmHg on days 1 and 5, respectively. CO decreased significantly (27 +/- 2%) and TPR increased (21 +/- 5%) on day 1; neither variable was significantly different from control on day 5. Plasma immunoreactive ANF levels were significantly elevated during acute (791 +/- 76 pg/ml) and chronic (626 +/- 202 pg/ml) ANF infusion compared with control values of approximately 100 pg/ml. The results indicate that elevations in plasma ANF within the pathophysiological range can significantly alter systemic hemodynamics, initially mediated by a decrease in CO. Autoregulatory phenomena may counteract these hemodynamic effects, returning CO to control levels and reducing TPR when the elevations in plasma ANF are chronically sustained.