Cardiovascular effects of angiotensin III in brainstem nuclei of normotensive and hypertensive rats.

The cardiovascular role of angiotensin III (ANG III) in the central nervous system is unclear. In this study, we investigated the hemodynamic effects of microinjection of ANG III and compared them with those of angiotensin II (ANG II) into the cerebral ventricle (i.c.v.), the area postrema (AP) and the nucleus tractus solitarii (NTS) of urethane-anesthetized rats. Male Sprague-Dawley rats [normal, renovascular hypertensive (2-kidney, 1-clip) and sham-operated groups] were used in this study. A dose-dependent pressor and bradycardic effect of ANG II and ANG III was observed after i.c.v. injection. When low doses of ANG II or ANG III were microinjected into both NTS and AP, a dose-dependent depressor and bradycardic effect were observed. The maximal depressor effect was observed at 9.6 pmol. When we increased the doses of ANG II or ANG III into the NTS, a pressor and tachycardic effect were observed. A significant difference of the cardiovascular effects of ANG III were noticed between renovascular hypertensive rats and sham-operated rats. The sympathetic nerve activity was inhibited by both pressor and depressor effects. The cardiovascular actions of both ANG II and ANG III were partially or completely abolished after pretreatment of their selective antagonists. These results indicate that the pressor effect of i.c.v. angiotensin are not mediated by activations of angiotensin receptors in the NTS or in the AP.