Effect of subpressor infusions of angiotensin on cardiovascular reactivity in the conscious rat.

Cardiovascular reactivity before and after 30 minutes and 20 hr Angiotensin infusions (40 ng/kg/min) has been studied in 26 male Wistar rats. Control responses to Tyramine (T) (0.05, 0.1 MG). Angiotensin (A) 10, 40, 160 ng), Norepinephrine (NE)(25, 100, 400 ng) and Renin (R)(0.05 G.U.) were obtained in the conscious animals with chronic cannulas in the aorta and jugular vein. Pressor responses to the same vasoactive agents were obtained immediately after A infusions. Similar 5% dextrose infusions were performed as controls. Results showed that pressor responses to T and A were significantly increased after 30 minutes A infusion and even more after 20 h infusion. Pressor responses to NE increase significantly only at the intermediate dose (100 ng) after 20 hr infusion. Response to R was potentiated by A infusion after 30 minutes and 20 hr. Dextrose infusions did not produce any significant changes in pressor responses.