CARDIOVASCULAR EFFECTS OF ANGIOTENSIN-III IN BRAIN-STEM NUCLEI OF NORMOTENSIVE AND HYPERTENSIVE RATS

The cardiovascular role of angiotensin III (ANG III) in the central ne rvous system is unclear. In this study, we investigated the hemodynami c effects of microinjection of ANG III and compared them with those of angiotensin II (ANG II) into the cerebral ventricle (i.c.v.), the are a postrema (AP) and the nucleus tractus solitarii (NTS) of urethane-an esthetized rats. Male Sprague-Dawley rats [normal, renovascular hypert ensive (2-kidney, 1-clip) and sham-operated groups] were used in this study. A dose-dependent presser and bradycardic effect of ANG II and A NG III was observed after i.c.v. injection. When low doses of ANG II o r ANG III were microinjected into both NTS and AP, a dose-dependent de pressor and bradycardic effect were observed. The maximal depressor ef fect was observed at 9.6 pmol. When we increased the doses of ANG II o r ANG III into the NTS, a presser and tachycardic effect were observed . A significant difference of the cardiovascular effects of ANG III we re noticed between renovascular hypertensive rats and sham-operated ra ts. The sympathetic nerve activity was inhibited by both presser and d epressor effects. The cardiovascular actions of both ANG II and ANG II I were partially or completely abolished after pretreatment of their s elective antagonists. These results indicate that the presser effect o f i.c.v. angiotensin are not mediated by activations of angiotensin re ceptors in the NTS or in the AP.