The pressor response to exogenous angiotensin I and its blockade by angiotensin II analogues in the American alligator

We examined the pressor response to exogenous, nonnative angiotensin I (ANG I; bullfrog, turtle, and fowl) in the conscious American alligator, Alligator mississippiensis. In addition, the inhibitory effects of three ANG II analogues ([Sar 1, Ala 8], [Sar 1, Thr 8], and [Sar 1, Ile 8]ANG II) on the pressor responses to angiotensin I (fowl ANG I, [Asp 1, Val 5, Ser 9]) were also examined. Intravenous administration of bullfrog, turtle, and fowl ANG I at 0.1, 0.5, and 1.0 μg/kg produced dose-dependent increases in arterial blood pressure. [Val 5]ANG II at 0.05, 0.1, and 0.5 μg/kg, or NE at 2 μg/kg also produced dose-dependent increases in blood pressure. [Sar 1, Ile 8]ANG II and [Sar 1, Ala 8]ANG II (10 μg/kg/min) both attenuated the pressor response to fowl ANG I whereas [Sar 1, Thr 8]ANG II (10 μg/kg/min) produced no significant blockade. These data demonstrate: (1) All three exogenous ANG I molecules exert potent vasopressor responses in the alligator, (2) [Sar 1, Ile 8]ANG II is the most effective ANG antagonist, and (3) the alligator appears to possess a renin-angiotensin system similar to that found in other vertebrates.