Effects of dehydration on cardiovascular development in the embryonic American alligator (Alligator mississipiensis)

Abstract

Effects of dehydration on reptilian embryonic cardiovascular function are unknown. Here, we present the first morphological and physiological data quantifying the cumulative effects of four acute dehydration events on the embryonic American alligator, Alligator mississipiensis. We hypothesized that dehydration would alter embryonic morphology, reduce blood volume and augment the response to angiotensin II (Ang II), a key osmotic and blood volume regulatory response element in adult vertebrates. Drying events at 30%, 40%, 50%, and 60% of embryonic incubation reduced total egg water content by 14.43±0.37g, a 3.4 fold increase relative to controls. However, embyronic blood volume was greater in the dehydration group at 70% of embryonic incubation compared to controls (0.39±0.044mLg−1 and 0.22±0.03mLg−1, respectively), however, both groups were similar at 90% of incubation (0.18±0.02mLg−1 in the controls and 0.23±0.03mLg−1 in the dehydrated group). Dehydration altered the morphological phenotype and resulted in an overall reduction in embryonic mass at both incubation time points measured. Dehydration also altered the physiological phenotype, resulting in embryonic alligators that were relatively bradycardic at 90% of incubation. Arterial Ang II injections resulted in a dose dependent hypertension, which increased in intensity over the span of incubation studied. While progressive incubation altered the Ang II response, dehydration had no impact on the cardiovascular responses to the peptide. Quantification of Ang II type-1 receptor protein using western blot analysis illustrated that dehydration condition and incubation time point did not alter protein quantity. Collectively, our results show that dehydration during embryonic development of the American alligator alters embryonic morphology and baseline heart rate without altering arterial pressure and response to Ang II.