Angiotensin II (ANG II) is a powerful vasoconstrictor of the renin-angiotensin system (RAS) that plays an important role in cardiovascular regulation in adult and developing vertebrates. Knowledge of ANG II's contribution to developmental cardiovascular function comes from studies in fetal mammals and embryonic chickens. This is the first study to examine the role of ANG II in cardiovascular control in an embryonic reptile, the American alligator (Alligator mississippiensis). Using chronic low (~ 5-mg kg embryo-1), or high doses (~ 450-mg kg embryo-1) of captopril, an angiotensin-converting enzyme (ACE) inhibitor, we disrupted the RAS and examined the influence of ANG II in cardiovascular function at 90% of embryonic development. Compared to embryos injected with saline, mean arterial pressure (MAP) was significantly reduced by 41 and 72% under low- and high-dose captopril treatments, respectively, a greater decrease in MAP than observed in other developing vertebrates following ACE inhibition. Acute exogenous ANG II injection produced a stronger hypertensive response in low-dose captopril-treated embryos compared to saline injection embryos. However, ACE inhibition with the low dose of captopril did not change adrenergic tone, and the ANG II response did not include an α-adrenergic component. Despite decreased MAP that caused a left shifted baroreflex curve for low-dose captopril embryos, ANG II did not influence baroreflex sensitivity. This study demonstrates that ANG II contributes to cardiovascular function in a developing reptile, and that the RAS contributes to arterial blood pressure maintenance during development across multiple vertebrate groups.
Keywords: Angiotensin-converting enzyme inhibitor; Baroreflex; Blood pressure; Heart rate; Reptile.