Involvement of neuropeptides and amino acids in central regulation of blood pressure.

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The experiments were undertaken in un-anesthetized and freely moving rats. 1)Renin and angiotensin II(AII)administered into the cerebroventricle caused pressor responses via stimulating AII receptors, which was potentiated in spontaneously hypertensive rats(SHR)than those in control Wistar Kyoto rats(WKY). 2)AII receptors involved in central pressor responses are found in the preoptic area(POA)and suprachiasmatic nucleus, but not in the central amygdaloid nucleus and paraventricular nucleus. The pressor responses are potentiated in SHR at only POA, and this hyperresponsiveness seems to be involved in not evocation but maintenance of hypertension, on the basis of differences between 6 and 15 weeks SHR. Pressor responses to AII are antagonized by central administration of GABA or taurine. The antagonism is not mediated by directly acting on POA, but by indirectly acting on other brain sites. 3)AII induced not only pressor responses but also an increase of water and salt intake, which are also potentiated in SHR. For this potentiation in fluid intakes, POA is also importantly involved. These responses to AII are antagonized by atrial natriuretic peptide(ANP)at POA and posterior hypothalamus(PH)in SHR but not in WKY, indicating responsiveness to ANP is also potentiated in SHR at those areas. The results suggest that the activities of brain AII and ANP neuronal system may play an important role in central controlling the cardiovascular system at POA and PH and is altered at these areas in genetically hypertensive rats.