RESUMEN
The dorsomedial nucleus of the hypothalamus (DMH) is part of the brain circuits that modulate organism responses to the circadian cycle, energy balance, and psychological stress. A large group of thyrotropin-releasing hormone (Trh) neurons is localized in the DMH; they comprise about one third of the DMH neurons that project to the lateral hypothalamus area (LH). We tested their response to various paradigms. In male Wistar rats, food restriction during adulthood, or chronic variable stress (CVS) during adolescence down-regulated adult DMH Trh mRNA levels compared to those in sedentary animals fed ad libitum; two weeks of voluntary wheel running during adulthood enhanced DMH Trh mRNA levels compared to pair-fed rats. Except for their magnitude, female responses to exercise were like those in male rats; in contrast, in female rats CVS did not change DMH Trh mRNA levels. A very strong negative correlation between DMH Trh mRNA levels and serum corticosterone concentration in rats of either sex was lost in CVS rats. CVS canceled the response to food restriction, but not that to exercise in either sex. TRH receptor 1 (Trhr) cells were numerous along the rostro-caudal extent of the medial LH. In either sex, fasting during adulthood reduced DMH Trh mRNA levels, and increased LH Trhr mRNA levels, suggesting fasting may inhibit the activity of TRHDMH->LH neurons. Thus, in Wistar rats DMH Trh mRNA levels are regulated by negative energy balance, exercise and chronic variable stress through sex-dependent and -independent pathways.
Asunto(s)
Hipotálamo , Hormona Liberadora de Tirotropina , Animales , Femenino , Masculino , Ratas , Corticosterona , Hipotálamo/metabolismo , Núcleo Talámico Mediodorsal , Actividad Motora , Ratas Wistar , Receptores de Hormona Liberadora de Tirotropina/genética , Receptores de Hormona Liberadora de Tirotropina/metabolismo , ARN Mensajero/metabolismo , Hormona Liberadora de Tirotropina/genética , Hormona Liberadora de Tirotropina/metabolismoRESUMEN
Starvation induces tertiary hypothyroidism in adult rodents. Response of the hypothalamus-pituitary-thyroid (HPT) axis to starvation is stronger in adult males than in females. To improve the description of this sexual dimorphism, we analyzed the dynamics of HPT axis response to fasting at multiple levels. In adult rats of the same cohort, 24 and 48 h of starvation inhibited paraventricular nucleus Trh expression and serum concentrations of TSH and T4 earlier in males than in females, with lower intensity in females than in males. In adult females fasted for 36-72 h, serum TSH concentration decreased after 36 h, when the activity of thyrotropin-releasing hormone (TRH)-degrading ectoenzyme was increased in the median eminence. The kinetics of these events were distinct from those previously observed in male rats. We suggest that the sex difference in TSH secretion kinetics is driven not only at the level of paraventricular nucleus TRH neurons, but also by differences in post-secretory catabolism of TRH, with enhancement of TRH-degrading activity more sustained in male than female animals.
Asunto(s)
Ayuno/metabolismo , Regulación de la Expresión Génica , Núcleo Hipotalámico Paraventricular/metabolismo , Glándula Tiroides/metabolismo , Animales , Femenino , Masculino , Ratas Wistar , Receptores de Hormona Liberadora de Corticotropina/genética , Receptores de Hormona Liberadora de Corticotropina/metabolismo , Receptores de Glucocorticoides/genética , Receptores de Glucocorticoides/metabolismo , Receptores de Hormona Liberadora de Tirotropina/genética , Receptores de Hormona Liberadora de Tirotropina/metabolismo , Factores Sexuales , Tirotropina/sangre , Tirotropina/metabolismo , Hormona Liberadora de Tirotropina/genética , Hormona Liberadora de Tirotropina/metabolismo , Factores de TiempoRESUMEN
Subthreshold electrical stimulation of the amygdala (kindling) activates neuronal pathways increasing the expression of several neuropeptides including thyrotropin releasing-hormone (TRH). Partial kindling enhances TRH expression and the activity or its inactivating ectoenzyme; once kindling is established (stage V), TRH and its mRNA levels are further increased but TRH-binding and pyroglutamyl aminopeptidase II (PPII) activity decreased in epileptogenic areas. To determine whether variations in TRH receptor binding or PPII activity are due to regulation of their synthesis, mRNA levels of TRH receptors (R1, R2) and PPII were semi-quantified by RT-PCR in amygdala, frontal cortex and hippocampus of kindled rats sacrificed at stage II or V. Increased mRNA levels of PPII were found at stage II in amygdala and frontal cortex, and of pro-TRH and TRH-R2, in amygdala and hippocampus. At stage V, pro-TRH mRNA levels increased and those of PPII, decreased in the three regions; TRH-R2 mRNA levels diminished in amygdala and frontal cortex and of TRH-R1 only in amygdala. In situ hybridization analyses revealed, at stage II, enhanced TRH-R1 mRNA levels in dentate gyrus and amygdala while decreased in piriform cortex; those of TRH-R2 increased in amygdala, CA2, dentate gyrus, piriform cortex, thalamus and subiculum and of PPII, in CAs and piriform cortex. In contrast, at stage V decreased expression of TRH-R1 occurred in amygdala, CA2/3, dentate gyrus and piriform cortex; of TRH-R2 in CA2, thalamus and piriform cortex, and of PPII in CA2, and amygdala. The magnitude of changes differed between ipsi and contralateral side. These results support a trans-synaptic modulation of all elements involved in TRH transmission in conditions that stimulate the activity of TRHergic neurons. They show that reported changes in PPII activity or TRH-binding caused by kindling relate to regulation of the expression of TRH receptors and degrading enzyme.
Asunto(s)
Amígdala del Cerebelo/fisiología , Regulación de la Expresión Génica/fisiología , Excitación Neurológica , Hormona Liberadora de Tirotropina/fisiología , Animales , Secuencia de Bases , Cartilla de ADN , Masculino , ARN Mensajero/genética , ARN Mensajero/metabolismo , Ratas , Ratas Wistar , Receptores de Hormona Liberadora de Tirotropina/genética , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
OBJECTIVE: Renin-angiotensin-aldosterone system component genes have been associated to essential hypertension. Thus, we studied the association of singe locus or multilocus interactions with young-onset essential hypertension. SETTING AND DESIGN: This is a case-control study based on a population sample of adolescent at an inner city. PARTICIPANTS: We studied 54 adolescents with hypertension and 121 age-matched normotensives, recruited from a high-school student population of 934 interviewed individuals. METHODS: Resting blood pressure was measured on three different days and normalized (Z-score) by sex and age. Genotypes of ACE (I/D) angiotensinogen (T174M and M235T), ATIR (A1166C), and CYP11B2 (C-344T) were determined by PCR/RFLP or ASO. RESULTS: Although genotype frequencies were not different in both groups, we found a significant dominant effect of ACE D and angiotensinogen 235T alleles on normalized systolic arterial blood pressure in males. This effect was confirmed by sib-pair linkage analysis taking normalized blood pressure as a quantitative trait. We independently analyzed multilocus interactions in normotensive and hypertensive adolescents searching for multiple locus deviation from Hardy-Weinberg or linkage equilibrium. We found that from 63 multilocus combinations, 4 deviated significantly from equilibrium in hypertensive adolescents but none in the normotensives. Deviations from equilibrium may indicate that the combination of alleles at different loci affects susceptibility or resistance to the disease. CONCLUSION: In addition to the angiotensin-converting enzyme (ACE) and angiotensinogen (AGT) gene variants, gene-gene interactions may be important causative factors in a complex disease such as young-onset essential hypertension.
Asunto(s)
Angiotensinógeno/genética , Hipertensión/genética , Oxidorreductasas actuantes sobre Donantes de Grupo CH-NH/genética , Peptidil-Dipeptidasa A/genética , Receptores de Hormona Liberadora de Tirotropina/genética , Sistema Renina-Angiotensina/genética , Adolescente , Estudios de Casos y Controles , Mapeo Cromosómico , Femenino , Frecuencia de los Genes , Humanos , Modelos Lineales , Masculino , Metilenotetrahidrofolato Reductasa (NADPH2) , Polimorfismo GenéticoRESUMEN
In essential hypertension, a polygenic and multifactorial syndrome, several genes interact with the environment to produce high blood pressure. Thyrotropin-releasing hormone (TRH) plays an important role in central cardiovascular regulation. We have described that TRH overexpression induces hypertension in a normal rat, which was reversed by TRH antisense treatment. This treatment also reduces the central TRH hyperactivity in spontaneously hypertensive rats and normalizes blood pressure. Human TRH receptor (TRHR) belongs to the G protein-coupled seven-transmembrane domain receptor superfamily. Mutations of these receptors may result in constitutive activation. As it has been demonstrated that hypertensive patients have a blunted TSH response to TRH injection, suggesting a defect in the TRHR, we postulate that the TRHR gene is involved in human hypertension. We studied 2 independent populations from different geographic regions of our country: a sample of adult subjects from a referral clinic and a population-based sample of high school students. In search of molecular variants of TRHR, we disclosed that a polymorphic TG dinucleotide repeat (STR) at -68 bp and a novel single nucleotide polymorphism, a G-->C conversion at -221 located in the promoter of the TRHR are associated with essential hypertension. As STRs detected in gene promoters are potential Z-DNA-forming sequences and seem to affect gene expression, we studied the potentially different transcriptional activity of these TRHR promoter variants and found that the S/-221C allele has a higher affinity than does the L/G-221 allele to nuclear protein factor(s). Our findings support the hypothesis that the TRHR gene participates in the etiopathogenesis of essential hypertension.
Asunto(s)
Hipertensión/genética , Receptores de Hormona Liberadora de Tirotropina/genética , Adolescente , Anciano , Alelos , Repeticiones de Dinucleótido/genética , Femenino , Frecuencia de los Genes , Genotipo , Humanos , Masculino , Persona de Mediana Edad , Polimorfismo de Nucleótido SimpleRESUMEN
Thyrotropin-releasing hormone (TRH) plays an important role in central cardiovascular regulation through the activation of different neurotransmitter systems at distinct extrahypothalamic sites. To study possible alterations in the TRH system in the hypertensive state, we measured TRH concentration in cerebrospinal fluid and TRH content of the preoptic area in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) by radioimmunoassay. In addition, we also measured the density of the TRH receptor in this area by a rapid filtration technique using [3H]methyl-TRH. We found a significant increase in both the TRH content (634 +/- 61 versus 350 +/- 26 pg/mg protein, SHR versus WKY; P < .01, n = 5) and density of TRH receptors without changes in affinity (Bmax, 5.0 +/- 0.1 versus 3.3 +/- 0.1 fmol/mg protein, P < .01, n = 4). An increase in TRH concentration was also found in the cerebrospinal fluid of SHR (30 +/- 3 versus 21 +/- 2 pg/mL, P < .01, n = 5), suggesting increased TRH release in the central nervous system. Northern blot analysis indicated a threefold augmented abundance of TRH precursor mRNA in the preoptic area of SHR. A polyclonal antibody raised against TRH injected peripherally or intracerebroventricularly lowered arterial blood pressure in SHR but not in WKY. In addition, long-term treatment with enalapril (5 mg/kg twice daily), which was effective in inhibiting serum angiotensin-converting enzyme activity by more than 50%, decreased arterial blood pressure and preoptic area TRH content of SHR, whereas another vasodilator, diltiazem (10 mg/kg every 8 hours), failed to produce a similar change.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Hipertensión/fisiopatología , Área Preóptica/química , Hormona Liberadora de Tirotropina/fisiología , Análisis de Varianza , Inhibidores de la Enzima Convertidora de Angiotensina/farmacología , Animales , Antihipertensivos/farmacología , Presión Sanguínea/efectos de los fármacos , Northern Blotting , Bloqueadores de los Canales de Calcio/farmacología , Diltiazem/administración & dosificación , Diltiazem/farmacología , Enalapril/administración & dosificación , Enalapril/farmacología , Hipertensión/tratamiento farmacológico , Hipertensión/etiología , Hipertensión/genética , Masculino , ARN Mensajero/análisis , Radioinmunoensayo , Ratas , Ratas Endogámicas SHR , Ratas Endogámicas WKY , Receptores de Hormona Liberadora de Tirotropina/análisis , Receptores de Hormona Liberadora de Tirotropina/genética , Hormona Liberadora de Tirotropina/análisis , Hormona Liberadora de Tirotropina/líquido cefalorraquídeo , Factores de Tiempo , Regulación hacia ArribaRESUMEN
This work examined whether (1) immune cells express thyrotrophin releasing hormone (TRH) receptor mRNA and (2) TRH modulates lymphocyte activation. By Northern blot of RNA extracted from human peripheral blood mononuclear cells (PBMC) and rat splenocytes, a single TRH receptor mRNA band of about 3.8 kb (identical to that obtained from pituitary cells) was obtained, under both basal and stimulated conditions. A significant increase in DNA synthesis was observed in phytohemagglutinin-stimulated PBMC and concanavalin A (Con A) stimulated splenocytes when TRH (10(-6) M-10(-12) M) was added. After 5, 30, 60, 180 min and 24 h of TRH administration in vivo, a significant increase in the rat splenocyte proliferative response to Con A was observed. In vivo administration of anti-rat TSH antibody (1/1000) blocked the increase observed after 30 min of TRH administration on the Con A stimulated splenocyte response. TRH possess immunostimulatory functions directly via its receptor and indirectly via release of other immunostimulatory factors such as thyrotrophin.