CROSSLEY, D. A.*; BAGATTO, B. P. ; HICKS, J. W.; ALTIMIRAS, J.: Changes in cardiovascular control mechanisms during the embryonic development of the American alligator, Alligator mississippiensis

Several ectothermic vertebrates possess a unique cardiac morphology that provides the potential for differential perfusion of systemic and pulmonary vasculatures. The crocodilians represent one such group with the capacity to bypass the lungs, returning deoxygenated blood to the systemic tissues (R-L shunt). Numerous studies have investigated cardiovascular function and control in adult crocodilians; however, maturation during embryonic development remains unknown. This study determined changes in cardiovascular function and control during the embryonic development (from 30 to 72 days) of the American alligator. During development resting cardiovascular function changed markedly, with mean arterial pressure rising from approximately 1kPa half way through incubation to 3 kPa at hatch. Heart rate remained relatively constant over development rising slightly from 80 to 90 beats per minute. Control mechanisms were comprised primarily of adrenergic systems with no tonic cholinergic input evident during alligator incubation. Baroreflex responses could be elicited initially at 70% of incubation with a progressive rise in sensitivity. Collectively the data suggest that embryonic control of cardiovascular function differs from that known to be present in adult aminals.