The effects of embryonic hypoxic programming on cardiovascular function and autonomic regulation in the American alligator (Alligator mississippiensis) at rest and during swimming
Reptilian embryos naturally experience fluctuating oxygen levels in ovo, and developmental hypoxia has been established to have long-term impacts on cardiovascular function in vertebrates. In the present study, we investigated the impact of developmental 21% (normoxia) and 10% O2 (hypoxia) on juvenile (4-year-old) American alligator cardiovascular function in animals at rest and during swimming. In both experimental groups, combined right aortic and right subclavian blood flow approximately doubled during swimming. Carotid blood flow increased during swimming in the hypoxia-programmed animals only, and both carotid and left aortic blood flow reached higher values in swimming hypoxic-programmed animals compared to the normoxic group. However, pulmonary blood flow, which increased two to threefold during swimming (in both groups), was higher in normoxic-programmed animals at both rest and swimming. The differences between programming groups were preserved after cholinergic blockade (atropine), but reduced by adrenergic receptor antagonists (propranolol and phentolamine). Propranolol and phentolamine also blunted the incremental increases in blood flows during swimming, which was especially clear in the hypoxia-programmed animals. Alteration in adrenergic control and relative cardiac size (which was increased in hypoxic-programmed alligators) may account for the differences between the experimental groups.