Expression of supressor of cytokine signaling (SOCS-3) in spontaneous hypertensive rat hypothalamus : effect on renal sodium excretion induced by angiotensin II

Abstract

Orientador: Jose Antonio Rocha GontijoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciencias MedicasResumo: A angiotensina II pode contribuir com o distúrbio do metabolismo renal de sódio presente em ratos espontaneamente hipertensos. Inicialmente, o estudo atentou à possibilidade de envolvimento da expressão do supressor de sinalização de citocinas (SOCS-3) (técnica de Western blotting) em hipotálamo de SHR durante o desenvolvimento hipertensivo (método indireto para medida de pressão arterial). Segundo, pós-estimulação aguda i.c.v com angiotensina II, avaliou a dipsogênese, o ritmo de filtração glomerular (técnica de clearance de creatinina), o manuseio tubular renal de sódio (técnica de clearance de lítio) e potássio em SHR e WKy. Os resultados obtidos confirmaram a estimulação central do receptor de angiotensina II e os seus efeitos dipsogênico e natriurético. A administração i.c.v de angiotensina II diminuiu o clearance de creatinina e, reciprocamente, aumentou a excreção tubular renal de sódio e de potássio nas duas linhagens, porém acentuadamente em WKy. Por outro lado, se comparada à diferença da expressão de JACK-2/SOCS-3 idade-dependente, a alteração da resposta funcional renal pós-estímulo intracerebroventricular com angiotensina II sugere uma disfunção das vias neurais existentes em animais SHR. As evidências supracitadas acrescentam à idéia existente na literatura que, a angiotensina II atuando no sistema nervoso central é um instrumento para regulação da homeostase do fluido corporal. Possivelmente, a resposta neural inapropriada resulte na inabilidade do manuseio hidrossalino e, conseqüentemente, colabore com o desenvolvimento da hipertensão arterial em SHR. Palavras-chave: Hipertensão arterial, SNC, angiotensina II; SOCS-3; SHR; função renal; natriurese; clearance de lítioAbstract: There is a surprising lack of experimental data on the renal sodium handle mechanisms induced by i.c.v injection of AngII in hypertensive animals. Thus, we hypothesized that a presumable blunted response to centrally injected AngII may contribute to sodium metabolism disturbances observed in SHR. The study was performed after acute i.c.v AngII administration on tubular sodium handling, evaluated by lithium clearance, in conscious, unrestrained rats and their sham-operated appropriate WKy controls. The present series of experiments were also designed to investigate the possible involvement of SOCS-3 expression in AngII-induced control of water ingestion in SHR hypothalamus. Our results confirm earlier reports on the potent natriuretic effects of central AngII receptor stimulation. The i.c.v application of AngII significantly decreased CCr and reciprocally promotes increased absolute and fractional excretion rates of sodium and potassium in both WKy and SHR animals. The magnitude of the renal response to AngII was significantly greater in WKy rats than in SHR. The enhancement of renal function following the centrally applied AngII in WKy rats as compared with SHR associated with age-related difference in JACK-2/SOCS-3 expression suggest that a dysfunction in the angiotensin neural pathways exists in SHR. Our findings lend further support to the idea that AngII in CNS is an instrumental in the regulation of body fluid homeostasis. Speculatively, it seems interesting to suggest that perhaps one of the CNS inappropriate AngII pathway response defects may result in inability of renal tubules to handle the hydrosaline balance, consequently may contributing with development of arterial hypertension in genetically hypertensive rats from Kyoto. Keywords: Arterial hypertension; central nervous system; angiotensin II; SOCS-3, SHR, kidney function; natriuresis; lithium clearanceDoutoradoDoutor em Farmacologi