RESUMO
In addition to being recognised for involvement in cardiovascular control and hydromineral balance, the renin-angiotensin system (RAS) has also been associated with the neuroendocrine control of energy balance. One of the main brain sites for angiotensin II (ANG II)/type 1 receptor (AT1 R) signalling is the subfornical organ (SFO), a circumventricular organ related to the control of autonomic functions, motivated behaviours and energy metabolism. Thus, we hypothesised that circulating ANG II may act on the SFO AT1 R receptors to integrate metabolic and hydromineral balance. We evaluated whether food deprivation can modulate systemic RAS activity and Agrt1a brain expression, and if ANG II/AT1 R signalling influences the hypothalamic expression of mRNAs encoding neuropeptides and food and water ingestion in fed and fasted Wistar rats. We found a significant increase in both ANG I and ANG II plasma levels after 24 and 48 h of fasting. Expression of Agrt1a mRNA in the SFO and paraventricular nucleus (PVN) also increased after food deprivation for 48 h. Treatment of fasted rats with low doses of losartan in drinking water attenuated the decrease in glycemia and meal-associated water intake without changing the expression in PVN or arcuate nucleus of mRNAs encoding selected neuropeptides related to energy homeostasis control. These findings point to a possible role of peripheral ANG II/SFO-AT1 R signalling in the control of refeeding-induced thirst. On the other hand, intracerebroventricular losartan treatment decreased food and water intake over dark time in fed but not in fasted rats.
Assuntos
Jejum , Órgão Subfornical , Animais , Masculino , Ratos , Angiotensina II/farmacologia , Encéfalo/metabolismo , Jejum/metabolismo , Losartan/farmacologia , Núcleo Hipotalâmico Paraventricular/metabolismo , Ratos Wistar , Receptor Tipo 1 de Angiotensina/metabolismo , Órgão Subfornical/metabolismoRESUMO
Maintenance of the volume and osmolality of body fluids is important, and the adaptive responses recruited to protect against osmotic stress are crucial for survival. The objective of this work was to compare the responses that occur in aging male and female rats during water deprivation. For this purpose, groups of male and female Wistar rats aged 3 mo (adults) or 18 mo (old) were submitted to water deprivation (WD) for 48 h. The water and sodium (0.15 M NaCl) intake, plasma concentrations of oxytocin (OT), arginine vasopressin (AVP), corticosterone (CORT), atrial natriuretic peptide (ANP), and angiotensin II (ANG II) were determined in hydrated and water-deprived animals. In response to WD, old male and female rats drank less water and saline than adults, and both adult and old females drank more water and saline than respective males. Dehydrated old animals displayed lower ANG II plasma concentration and CORT response compared with the respective normohydrated rats. Dehydrated adult males had higher plasma ANP and AVP as well as lower CORT concentrations than dehydrated adult females. Moreover, plasma OT and CORT levels of old female rats were higher than those in the dehydrated old male rats. Relative expression of ANG II type 1 receptor mRNA was decreased in the subfornical organ of adult and old male rats as well as adult female rats in response to WD. In conclusion, the study elucidated the effect of sex and age on responses induced by WD, altering the degree of dehydration induced by 48 h of WD.
Assuntos
Fatores Etários , Comportamento Animal/fisiologia , Desidratação/fisiopatologia , Fatores Sexuais , Privação de Água/fisiologia , Animais , Arginina Vasopressina/metabolismo , Ingestão de Líquidos/efeitos dos fármacos , Feminino , Masculino , Ratos Wistar , Cloreto de Sódio/farmacologia , Órgão Subfornical/metabolismoRESUMO
Angiotensin II (Ang II) acts on Ang II type 1 (AT1) receptors located in the organum vasculosum and subfornical organ (SFO) of the lamina terminalis as a main facilitatory mechanism of sodium appetite. The brain serotonin (5-HT) system with soma located in the dorsal raphe nucleus (DRN) provides a main inhibitory mechanism. In the present study, we first investigated the existence of Ang II AT1 receptors in serotonergic DRN neurones. Then, we examined whether whole body sodium depletion affects the gene expression of the AT1a receptor subtype and the presumed functional significance of AT1 receptors. Using confocal microscopy, we found that tryptophan hydroxylase-2 and serotonin neurones express AT1 receptors in the DRN. Immunofluorescence quantification showed a significant reduction in 5-HT content but no change in AT1 receptor expression or AT1/5-HT colocalisation in the DRN after sodium depletion. Whole body sodium depletion also significantly increased Agtr1a mRNA expression in the SFO and DRN. Oral treatment with the AT1 receptor antagonist losartan reversed the changes in Agtr1a expression in the SFO but not the DRN. Losartan injection into either the DRN or the mesencephalic aqueduct had no influence on sodium depletion-induced 0.3 mol L-1 NaCl intake. The results indicate the expression of Agtr1a mRNA in the DRN and SFO as a marker of sodium depletion. They also suggest that serotonergic DRN neurones are targets for Ang II. However, the function of their AT1 receptors remains elusive.
Assuntos
Núcleo Dorsal da Rafe/metabolismo , Expressão Gênica , Receptor Tipo 1 de Angiotensina/genética , Serotonina/análise , Sódio/deficiência , Bloqueadores do Receptor Tipo 1 de Angiotensina II/farmacologia , Animais , Apetite/fisiologia , Núcleo Dorsal da Rafe/química , Imunofluorescência , Expressão Gênica/fisiologia , Losartan/farmacologia , Masculino , Neurônios/química , RNA Mensageiro/análise , Ratos , Ratos Wistar , Receptor Tipo 1 de Angiotensina/análise , Receptor Tipo 1 de Angiotensina/fisiologia , Sódio/sangue , Órgão Subfornical/química , Órgão Subfornical/metabolismo , Triptofano Hidroxilase/análiseRESUMO
NEW FINDINGS: What is the central question of this study? The central goal of this study was to understand the effects of central angiotensin-(1-7) on basal and osmotically stimulated water intake in rats. What is the main finding and its importance? This study demonstrated that central administration of angiotensin-(1-7) did not induce thirst in basal conditions but increased water intake after osmotic stimulation, such as water deprivation and salt loading. These results indicate a new function for this peptide, which, in turn, allows for future research on the mechanisms through which angiotensin-(1-7) influences osmotic thirst. Angiotensin-(1-7) [Ang-(1-7)] is generated by type 2 angiotensin-converting enzyme (ACE2) and binds to the MAS receptor. Although it is well known that Ang-(1-7) functionally antagonizes the effects of the classical renin-angiotensin system in several situations, the role of Ang-(1-7) in hydromineral homeostasis is not clear. The aim of this study was to assess the role of Ang-(1-7) on neuroendocrine responses to hyperosmolality in rats. Male Wistar rats were divided into the following three groups: control; 24 h of water deprivation (WD); and 24 h of salt loading (SL; 1.8% NaCl). Intracerebroventricular (i.c.v.) injections of Ang-(1-7) or vehicle were given to assess water intake and plasma concentration of vasopressin. Additionally, the brains from control and WD groups were collected to evaluate gene expression in the subfornical organ (SFO), paraventricular nucleus (PVN) and supraoptic nucleus (SON). It was found that i.c.v. Ang-(1-7) did not change water and salt intake in control rats; however, Ang-(1-7) increased water intake after WD and SL, with no change in salt intake. Plasma vasopressin was not changed by i.c.v. Ang-(1-7) in control or WD rats. Moreover, WD increased Mas gene expression in the SON and PVN, with no changes in Ace2 mRNA levels. In conclusion, Ang-(1-7) increases thirst after osmotic stimuli, indicating that a previous sensitization to its action is necessary. This finding is consistent with the increased Mas gene expression in the PVN and SON after water deprivation.
Assuntos
Angiotensina I/administração & dosagem , Ingestão de Líquidos/efeitos dos fármacos , Pressão Osmótica , Núcleo Hipotalâmico Paraventricular/efeitos dos fármacos , Fragmentos de Peptídeos/administração & dosagem , Órgão Subfornical/efeitos dos fármacos , Núcleo Supraóptico/efeitos dos fármacos , Sede/efeitos dos fármacos , Enzima de Conversão de Angiotensina 2 , Animais , Injeções Intraventriculares , Masculino , Núcleo Hipotalâmico Paraventricular/metabolismo , Peptidil Dipeptidase A/genética , Peptidil Dipeptidase A/metabolismo , Proto-Oncogene Mas , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas/metabolismo , Ratos Wistar , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismo , Cloreto de Sódio/administração & dosagem , Órgão Subfornical/metabolismo , Núcleo Supraóptico/metabolismo , Regulação para Cima , Vasopressinas/sangue , Privação de ÁguaRESUMO
Water deprivation (WD) induces changes in plasma volume and osmolality, which in turn activate several responses, including thirst, the activation of the renin-angiotensin system (RAS) and vasopressin (AVP) and oxytocin (OT) secretion. These systems seem to be influenced by oestradiol, as evidenced by the expression of its receptor in brain areas that control fluid balance. Thus, we investigated the effects of oestradiol treatment on behavioural and neuroendocrine changes of ovariectomized rats in response to WD. We observed that in response to WD, oestradiol treatment attenuated water intake, plasma osmolality and haematocrit but did not change urinary volume or osmolality. Moreover, oestradiol potentiated WD-induced AVP secretion, but did not alter the plasma OT or angiotensin II (Ang II) concentrations. Immunohistochemical data showed that oestradiol potentiated vasopressinergic neuronal activation in the lateral magnocellular PVN (PaLM) and supraoptic (SON) nuclei but did not induce further changes in Fos expression in the median preoptic nucleus (MnPO) or subfornical organ (SFO) or in oxytocinergic neuronal activation in the SON and PVN of WD rats. Regarding mRNA expression, oestradiol increased OT mRNA expression in the SON and PVN under basal conditions and after WD, but did not induce additional changes in the mRNA expression for AVP in the SON or PVN. It also did not affect the mRNA expression of RAS components in the PVN. In conclusion, our results show that oestradiol acts mainly on the vasopressinergic system in response to WD, potentiating vasopressinergic neuronal activation and AVP secretion without altering AVP mRNA expression.
Assuntos
Desidratação/fisiopatologia , Estradiol/uso terapêutico , Estrogênios/uso terapêutico , Neurônios/efeitos dos fármacos , Núcleo Hipotalâmico Paraventricular/efeitos dos fármacos , Núcleo Supraóptico/efeitos dos fármacos , Desequilíbrio Hidroeletrolítico/prevenção & controle , Animais , Arginina Vasopressina/agonistas , Arginina Vasopressina/análise , Arginina Vasopressina/metabolismo , Comportamento Animal/efeitos dos fármacos , Desidratação/terapia , Ingestão de Líquidos/efeitos dos fármacos , Terapia de Reposição de Estrogênios , Feminino , Hidratação , Regulação da Expressão Gênica/efeitos dos fármacos , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Neurônios/metabolismo , Neurônios/patologia , Ovariectomia/efeitos adversos , Núcleo Hipotalâmico Paraventricular/metabolismo , Núcleo Hipotalâmico Paraventricular/patologia , Área Pré-Óptica/efeitos dos fármacos , Área Pré-Óptica/metabolismo , Área Pré-Óptica/patologia , Ratos Wistar , Órgão Subfornical/efeitos dos fármacos , Órgão Subfornical/metabolismo , Órgão Subfornical/patologia , Núcleo Supraóptico/metabolismo , Núcleo Supraóptico/patologia , Núcleo Vestibular Lateral/efeitos dos fármacos , Núcleo Vestibular Lateral/metabolismo , Núcleo Vestibular Lateral/patologia , Desequilíbrio Hidroeletrolítico/sangue , Desequilíbrio Hidroeletrolítico/etiologia , Desequilíbrio Hidroeletrolítico/fisiopatologiaRESUMO
Blood-borne angiotensin-II (Ang-II) has profound effects in the brain. We tested the hypothesis that Ang-II-dependent hypertension involves differential Ang-II type I (AT(1)) receptors expression in the subfornical organ (SFO) and the rostral ventrolateral medulla (RVLM). Male Wistar rats were implanted with 14-day osmotic minipump filled with Ang-II (150 ng/kg/min) or saline. AT(1) receptor mRNA levels were detected in the SFO and RVLM by reverse transcription-polymerase chain reaction (RT-PCR). Ang-II caused hypertension (134 ± 10 mmHg vs. 98 ± 9 mmHg, n = 9, p < 0.05). RT-PCR revealed that Ang-II infusion induced increased AT(1) receptor mRNA levels in RVLM and decreased in SFO. Our data suggest that Ang-II-induced hypertension involves differential expression of brain AT(1) receptors.
Assuntos
Angiotensina II/metabolismo , Hipertensão/metabolismo , Bulbo/metabolismo , Receptor Tipo 1 de Angiotensina/genética , Órgão Subfornical/metabolismo , Animais , Hipertensão/induzido quimicamente , Masculino , RNA Mensageiro/genética , Ratos , Ratos Wistar , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de SinaisRESUMO
Neurogenic hypertension has been the subject of extensive research worldwide. This review is based on the premise that some forms of neurogenic hypertension are caused in part by the formation of angiotensin-II (Ang-II)-induced reactive oxygen species along the subfornical organ-paraventricular nucleus of the hypothalamus-rostral ventrolateral medulla pathway (SFO-PVN-RVLM pathway). We will discuss the recent contribution of our laboratory and others regarding the mechanisms by which neurons in the SFO (an important circumventricular organ) are activated by Ang-II, how the SFO communicates with two other important areas involved in sympathetic activity regulation (PVN and RVLM) and how Ang-II-induced reactive oxygen species participate along the SFO-PVN-RVLM pathway in the pathogenesis of neurogenic hypertension.
Assuntos
Humanos , Angiotensina II/fisiologia , Hipertensão/etiologia , Bulbo/metabolismo , Núcleo Hipotalâmico Paraventricular/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Órgão Subfornical/metabolismo , Angiotensina II/biossíntese , Neurônios/metabolismoRESUMO
Neurogenic hypertension has been the subject of extensive research worldwide. This review is based on the premise that some forms of neurogenic hypertension are caused in part by the formation of angiotensin-II (Ang-II)-induced reactive oxygen species along the subfornical organ-paraventricular nucleus of the hypothalamus-rostral ventrolateral medulla pathway (SFO-PVN-RVLM pathway). We will discuss the recent contribution of our laboratory and others regarding the mechanisms by which neurons in the SFO (an important circumventricular organ) are activated by Ang-II, how the SFO communicates with two other important areas involved in sympathetic activity regulation (PVN and RVLM) and how Ang-II-induced reactive oxygen species participate along the SFO-PVN-RVLM pathway in the pathogenesis of neurogenic hypertension.
Assuntos
Angiotensina II/fisiologia , Hipertensão/etiologia , Bulbo/metabolismo , Núcleo Hipotalâmico Paraventricular/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Órgão Subfornical/metabolismo , Angiotensina II/biossíntese , Humanos , Neurônios/metabolismoRESUMO
Blood-borne angiotensin II (Ang II) has profound effects on the central nervous system, including regulation of vasopressin secretion and modulation of sympathetic outflow. However, the mechanism by which circulating Ang II affects the central nervous system remains largely unknown. We tested the hypothesis that increased circulating levels of Ang II activate angiotensin type I (AT1) receptors in the subfornical organ (SFO), increasing the Ang II signalling in the rostral ventrolateral medulla (RVLM). Male Wistar rats were subcutaneously implanted with two 14-day osmotic minipumps filled with Ang II (150 ng/kg/minute), Losartan (10mg/kg/day), or saline. In addition, AT1 receptor mRNA levels in the SFO and RVLM were detected by reverse transcription polymerase chain reaction (RT-PCR). Infusion of Ang II-induced hypertension (134 ± 10 mmHg vs 98 ± 9 mmHg, n = 9, p < 0.05), which was blunted by concomitant infusion of Losartan (105 ± 8 vs 134 ± 10 mmHg, n = 9, p < 0.05). In addition, hexamethonium produced a greater decrease in blood pressure in Ang II-infused rats. Real time PCR revealed that chronic Ang II infusion induced an increase in AT1 receptor mRNA levels in the RVLM and a decrease in the SFO. Taken together, using combined in vivo and molecular biology approaches, our data suggest that Ang II-induced hypertension is mediated by an increase in sympathetic nerve activity, which seems to involve up-regulation of AT1 receptors in the RVLM and down-regulation of AT1 receptors in the SFO.
Assuntos
Angiotensina II/administração & dosagem , Angiotensina II/farmacologia , Bulbo/efeitos dos fármacos , Bulbo/metabolismo , Receptor Tipo 1 de Angiotensina/metabolismo , Órgão Subfornical/efeitos dos fármacos , Órgão Subfornical/metabolismo , Animais , Pressão Sanguínea/efeitos dos fármacos , Regulação da Expressão Gênica/efeitos dos fármacos , Hipertensão/genética , Hipertensão/fisiopatologia , Losartan/farmacologia , Masculino , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Endogâmicos SHR , Ratos Wistar , Receptor Tipo 1 de Angiotensina/genética , Sistema Nervoso Simpático/efeitos dos fármacos , Sistema Nervoso Simpático/fisiopatologiaRESUMO
The spontaneously hypertensive rat (SHR) has an intense consumption of NaCl solution. Water deprivation (WD) followed by water intake to satiety induces partial rehydration (PR)-the WD-PR protocol-and sodium appetite. In the present work, WD produced similar water intake and no alterations in arterial pressure among spontaneously hypertensive rat (SHR), Wistar-Kyoto, and Holtzman strains. It also increased the number of cells with positive c-Fos immunoreactivity (Fos-IR) in the lamina terminalis and in the hypothalamic supraoptic (SON) and paraventricular (parvocellular, PVNp) nucleus in these strains. The WD and WD-PR produced similar alterations in all strains in serum osmolality and protein, plasma renin activity, and sodium balance. The SHR ingested about 10 times more 0.3 M NaCl than normotensives strains in the sodium appetite test that follows WD-PR. After WD-PR, the Fos-IR persisted, elevated in the lamina terminalis of all strains but notably in the subfornical organ of the SHR. The WD-PR reversed Fos-IR in the SON of all strains and in the PVNp of SHR. It induced Fos-IR in the area postrema and in the nucleus of the solitary tract (NTS), dorsal raphe, parabrachial (PBN), pre-locus coeruleus (pre-LC), suprachiasmatic, and central amygdalar nucleus of all strains. This effect was bigger in the caudal-NTS, pre-LC, and medial-PBN of SHRs. The results indicate that WD-PR increases cell activity in the forebrain and hindbrain areas that control sodium appetite in the rat. They also suggest that increased cell activity in facilitatory brain areas precedes the intense 0.3 M NaCl intake of the SHR in the sodium appetite test.
Assuntos
Apetite/fisiologia , Hipertensão/metabolismo , Hipotálamo/metabolismo , Proteínas Proto-Oncogênicas c-fos/metabolismo , Cloreto de Sódio na Dieta/farmacologia , Privação de Água/fisiologia , Tonsila do Cerebelo/metabolismo , Animais , Pressão Sanguínea/fisiologia , Ingestão de Líquidos/fisiologia , Ingestão de Alimentos/fisiologia , Eletrólitos/sangue , Eletrólitos/urina , Frequência Cardíaca/fisiologia , Hipertensão/fisiopatologia , Imuno-Histoquímica , Masculino , Área Pré-Óptica/metabolismo , Ratos , Ratos Endogâmicos SHR , Ratos Endogâmicos WKY , Ratos Sprague-Dawley , Órgão Subfornical/metabolismo , Equilíbrio Hidroeletrolítico/fisiologiaRESUMO
Angiotensin II (Ang II) receptors in specific brain areas and in the anterior pituitary are controlled by reproductive hormones. Since Ang II also plays a role in controlling reproductive functions, such as luteinizing hormone and prolactin secretion, the objective of the present study was to evaluate the regulation of Ang II receptors by estradiol (E(2)) and progesterone (P) in areas of the brain involved in homeostatic and reproductive functions, such as the locus coeruleus (LC), median preoptic nucleus (MnPO) and subfornical organ (SFO). Adult female rats were ovariectomized under anesthesia and divided into 2 groups after 2 weeks: OVX plus E(2)/P replacement (OVXE(2)P) and OVX plus oil vehicle (OVX). E(2) was injected for 3 consecutive days followed by an injection of P on the 4th day. Animals were killed by decapitation and the brains were removed and frozen. Consecutive coronal brain sections were cut in a cryostat and Ang II receptors were quantified by autoradiography in the MnPO, LC and SFO. Treatment of OVX rats with E(2) and P induced a significant increase in the Ang II receptor binding (fmol/mg protein) in the MnPO (OVX: 4.48 +/- 0.58 and OVXE(2)P: 9.89 +/- 1.65), LC (OVX: 2.72 +/- 0.37 and OVXE(2)P: 8.03 +/- 0.9) and SFO (OVX: 5.45 +/- 0.66 and OVXE(2)P: 10.73 +/- 1.79) compared to OVX animals treated with the vehicle, P < 0.05. In conclusion, these results show that Ang II receptors are upregulated by E(2) and P in the LC, MnPO and SFO of ovariectomized rats.
Assuntos
Estradiol/farmacologia , Locus Cerúleo/metabolismo , Área Pré-Óptica/metabolismo , Progesterona/farmacologia , Receptores de Angiotensina/efeitos dos fármacos , Órgão Subfornical/metabolismo , Anestesia , Animais , Autorradiografia , Feminino , Locus Cerúleo/efeitos dos fármacos , Ovariectomia , Área Pré-Óptica/efeitos dos fármacos , Ratos , Ratos Wistar , Órgão Subfornical/efeitos dos fármacos , Regulação para Cima/efeitos dos fármacosRESUMO
We investigated the effect of endothelins (ETs) on receptor-mediated phosphoinositides (PI) turnover in whole subfornical organ (SFO) and median eminence (ME). Consistent with the presence of a high density of binding sites in the SFO and the ME of the rat brain, our results show an increase in PI hydrolysis induced by ETs in each structure, in a dose-dependent manner and with similar ED50 values. In addition, IRL 1620, a selective ETB receptor agonist, increased the inositol monophosphate (InsP1) accumulation in the SFO and the ME in a similar degree as ETs. With the use of selective agonists and antagonists of both endothelin receptor subtypes, we characterized the receptor subtype involved in ET-induced phosphoinositide metabolism. The addition of two selective ETA receptor antagonists, BQ 123 or BQ 610, did not alter the ETs-induced increase in the PI metabolism. While, IRL 1620- and ET3-induced InsP1 accumulation was completely blocked by BQ 788, a selective ETB receptor antagonist, in both brain structures evaluated. Our results demonstrate that in the SFO and the ME of the rat brain, stimulation of phosphoinositide turnover constitutes one of the signaling pathways of ETs, and this action is mediated through ETB receptor activation. These results support the concept that endothelin could play a role in the regulation of brain functions.
Assuntos
Endotelina-1/farmacologia , Endotelina-3/farmacologia , Eminência Mediana/metabolismo , Receptor de Endotelina B/metabolismo , Transdução de Sinais/fisiologia , Órgão Subfornical/metabolismo , Animais , Anti-Hipertensivos/metabolismo , Anti-Hipertensivos/farmacologia , Sítios de Ligação , Relação Dose-Resposta a Droga , Antagonistas do Receptor de Endotelina A , Antagonistas do Receptor de Endotelina B , Endotelina-1/metabolismo , Endotelina-3/metabolismo , Masculino , Eminência Mediana/efeitos dos fármacos , Oligopeptídeos/metabolismo , Oligopeptídeos/farmacologia , Peptídeos Cíclicos/metabolismo , Peptídeos Cíclicos/farmacologia , Fosfatidilinositóis/metabolismo , Ratos , Ratos Sprague-Dawley , Receptor de Endotelina A/metabolismo , Órgão Subfornical/efeitos dos fármacosRESUMO
1. Neural angiotensinergic circuitry located in the lamina terminalis has been proposed to be involved in blood pressure regulation and fluid homeostasis. 2. ANG II binding sites have been described to be localized throughout the lamina terminalis including the subfornical organ (SFO), the median preoptic nucleus (MnPO), and the organum vasculosum lamina terminalis (OVLT). 3. The present experiment was designed to investigate the ANG II binding sites localization in the lamina terminalis. For this purpose, we have compared the ANG II binding sites, acetylcholinesterase, and NADPH-diaphorase distributions throughout the lamina terminalis. Additionally, we have studied the effect of the preferential lesion of SFO neuronal cell bodies by local injection of NMDA on the ANG II binding sites density in different areas of the lamina terminalis. 4. Male Wistar rats were anesthetized, immobilized in a stereotaxic apparatus, and 500 nl of saline or 250 nmol NMDA was injected into the SFO. 5. Animals were sacrificed 1 week later, the brain was removed, frozen, and sagittal 16 microm slices were cut in a cryostat. Alternate brain slices were incubated with [125I]-Sar1-ANG II for receptor autoradiography or histochemically stained for visualization of acetylcholinesterase and NADPH-diaphorase activities. Binding capacity was determined by computerized quantitative densitometry of autoradiograms. The intensity of histochemical reactions was measured as relative units obtained by computerized densitometry processing of the brain slices stained for either activity. 6. Acetylcholinesterase staining was mainly located in the SFO, with faint staining reaction in other areas of the lamina terminalis. NADPH-diaphorase staining was homogeneously distributed throughout the lamina terminalis. A significant positive correlation was observed between acetylcholinesterase and NADPH-diaphorase stainings in the SFO of control and NMDA-lesioned rats. 7. ANG II binding sites were localized throughout the lamina terminalis. A significant positive correlation was observed between the density of ANG II binding sites and the intensity of acetylcholinesterase or NADPH-diaphorase staining in the SFO of control and NMDA-lesioned rats. 8. The distribution of the NADPH-diaphorase staining was found to closely match the distribution of the ANG II binding sites in the lamina terminalis. 9. Neuronal lesion of the SFO caused significant reductions in the density of ANG II biding sites in the SFO (-68%) and the MnPO (-48%). No changes were observed either in the OVLT or outside the lamina terminalis in the superior colliculus. 10. The present results indicate the following: first, the presence of high levels of acetylcholinesterase staining in the SFO and of NADPH-diaphorase throughout the lamina terminalis; second, that ANG II binding sites in the SFO and possibly in the MnPO are localized in neuronal cell bodies; third, that SFO lesion did not affect the expression of ANG II binding sites in the OVLT, thus suggesting that these binding sites correspond to different angiotensinergic system: and finally, the existence of a striking correlation between the distribution of the ANG II binding sites and NADPH-diaphorase throughout the lamina terminalis, thus suggesting a interrelation between angiotensinergic and nitrergic systems in the lamina terminalis.
Assuntos
Acetilcolinesterase/metabolismo , Angiotensina II/metabolismo , Hipotálamo/metabolismo , NADPH Desidrogenase/metabolismo , Órgão Subfornical/metabolismo , Animais , Autorradiografia , Denervação , Agonistas de Aminoácidos Excitatórios , Hipotálamo/citologia , Masculino , N-Metilaspartato , Neurônios/enzimologia , Área Pré-Óptica/citologia , Área Pré-Óptica/metabolismo , Ratos , Ratos Wistar , Órgão Subfornical/citologiaRESUMO
The circumventricular structures and the lateral hypothalamus (LH) have been shown to be important for the central action of angiotensin II (ANGII) on water and electrolyte regulation. Several anatomical findings have demonstrated neural connection between circumventricular structures and the LH. The present experiments were conducted to investigate the role of the alpha-adrenergic antagonists and agonistic injected into the LH on the water intake, sodium and potassium excretion elicited by injections of ANGII into the lateral ventricle (LV). The water intake was measured every 30 min over a period of 120 min. The sodium, potassium and urinary volume were measured over a period of 120 min in water-loaded rats. The injection of ANGII into the LV increased the water intake, which was reduced by previous injection of clonidine (an alpha-2-adrenergic agonist) into the LH. The injection of yohimbine (an alpha-2-adrenergic antagonist) and prazosin (an alpha-1-adrenergic antagonist) into the LH, which was done before injecting ANGII into the LV, also reduced the water intake induced by ANGII. The injection of ANGII into the LV reduced the sodium, potassium and urinary volume. Previous treatment with clonidine attenuated the action of ANGII in reducing the sodium, potassium and urinary volume, whereas previous treatment with yohimbine attenuated the effects of ANGII but with less intensity than that caused by clonidine. Previous treatment with prazosin increased the inhibitory effects of ANGII in those parameters. The injection of yohimbine and prazosin, which was done before the injection of clonidine, attenuated the effect of clonidine on the ANGII mechanism. The results of this study led us to postulate that when alpha-2-adrenergic receptors are blocked, the clonidine may act on the imidazoline receptors to produce its effects on the ANGII mechanism. We may also conclude that the LH is involved with circumventricular structures, which present excitatory and inhibitory mechanisms. Such mechanisms are responsible for regulating the renal excretion of sodium, potassium and water.
Assuntos
Angiotensina II/farmacologia , Ingestão de Líquidos/fisiologia , Região Hipotalâmica Lateral/metabolismo , Potássio/urina , Receptores Adrenérgicos alfa 1/metabolismo , Receptores Adrenérgicos alfa 2/metabolismo , Sódio/urina , Angiotensina II/metabolismo , Animais , Clonidina/farmacologia , Ingestão de Líquidos/efeitos dos fármacos , Esquema de Medicação , Interações Medicamentosas/fisiologia , Região Hipotalâmica Lateral/citologia , Região Hipotalâmica Lateral/efeitos dos fármacos , Injeções Intraventriculares , Rim/efeitos dos fármacos , Rim/fisiologia , Masculino , Vias Neurais/citologia , Vias Neurais/efeitos dos fármacos , Vias Neurais/metabolismo , Neurônios/citologia , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Prazosina/farmacologia , Ratos , Ratos Sprague-Dawley , Receptores Adrenérgicos alfa 1/efeitos dos fármacos , Receptores Adrenérgicos alfa 2/efeitos dos fármacos , Órgão Subfornical/citologia , Órgão Subfornical/efeitos dos fármacos , Órgão Subfornical/metabolismo , Ioimbina/farmacologiaRESUMO
The effects of atrial natriuretic factor (ANF) on norepinephrine (NE) uptake in circumventricular organs (organum vasculosum lamina terminalis, organum subfornicale and area postrema), locus coeruleus and nucleus tractus solitarii were studied in the rat. Experiments were carried out in vitro using nuclei obtained according to the punch-out technique. Results showed that 100 nM ANF enhanced NE uptake in all nuclei studied. These results suggest that ANF may be indirectly related to the control of cardiocirculatory functions, hydroelectrolyte balance, neuroendocrine secretions, nutrient and metabolic homeostasis, through the modulation of noradrenergic neurotransmission at the neuronal presynaptic level.