CARDIOVASCULAR EFFECTS PRODUCED BY MICROINJECTION OF ANGIOTENSINS ANDANGIOTENSIN ANTAGONISTS INTO THE VENTROLATERAL MEDULLA OF FREELY MOVING RATS

In this study we determined the cardiovascular effects produced by mic roinjection of angiotensin peptides [Angiotensin-(1-7) and Angiotensin II] and angiotensin antagonists (losartan, L-158,809, CGP 42112A, Sar (1)-Thr(8)-Ang II, A-779) into the rostral ventrolateral medulla of fr eely moving rats. Microinjection of angiotensins (12.5-50 pmol) produc ed presser responses associated to variable changes in heart rate, usu ally tachycardia. Unexpectedly, microinjection of both AT(1) and AT(2) ligands produced presser effects at doses that did not change blood p ressure in anesthetized rats. Conversely, microinjection of Sar(1)-Thr (8)-Ang II and the selective Ang-(1-7) antagonist, A-779, produced a s mall but significant decrease in MAP an HR. These findings suggest tha t angiotensins can influence the tonic activity of vasomotor neurons a t the RVLM. As previously observed in anesthetized rats, our results f urther suggest a role for endogenous Ang-(1-7) at the RVLM. The presse r activity of the ligands for AT(1) and AT(2) angiotensin receptor sub types at the RVLM; remains to be clarified.