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 ([Sar1, Ala8], [Sar1, Thr8], and [Sar1, Ile8]ANG II) on the pressor responses to angiotensin I (fowl ANG I, [Asp1, Val5, Ser9]) were also examined. Intravenous administration of bullfrog, turtle, and fowl ANG I at 0.1, 0.5, and 1.0 micrograms/kg produced dose-dependent increases in arterial blood pressure. [Val5]ANG II at 0.05, 0.1, and 0.5 micrograms/kg, or NE at 2 micrograms/kg also produced dose-dependent increases in blood pressure. [Sar1, Ile8]ANG II and [Sar1, Ala8]ANG II (10 micrograms/kg/min) both attenuated the pressor response to fowl ANG I whereas [Sar1, Thr8]ANG II (10 micrograms/kg/min) produced no significant blockade. These data demonstrate: (1) All three exogenous ANG I molecules exert potent vasopressor responses in the alligator, (2) [Sar1, Ile8]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.