Cardiovascular effects produced by microinjection of angiotensins and angiotensin antagonists into the ventrolateral medulla of freely moving rats

In this study we determined the cardiovascular effects produced by microinjection 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 freely moving rats. Microinjection of angiotensins (12.5-50 pmol) produced presser responses associated to variable changes in heart rate, usually tachycardia. Unexpectedly, microinjection of both AT(1) and AT(2) ligands produced presser effects at doses that did not change blood pressure in anesthetized rats. Conversely, microinjection of Sar(1)-Thr(8)-Ang II and the selective Ang-(1-7) antagonist, A-779, produced a small but significant decrease in MAP an HR. These findings suggest that angiotensins can influence the tonic activity of vasomotor neurons at the RVLM. As previously observed in anesthetized rats, our results further suggest a role for endogenous Ang-(1-7) at the RVLM. The presser activity of the ligands for AT(1) and AT(2) angiotensin receptor subtypes at the RVLM; remains to be clarified.