Hypoxic alligator embryos: Chronic hypoxia, catecholamine levels and autonomic responses of in ovo alligators

Abstract

Embryonic alligator responses to adrenergic blockade with propranolol and phentolamine were very similar to previously reported responses of embryonic chicken, and demonstrated that embryonic alligator have α and β-adrenergic tone over the final third of development. However, adrenergic tone originates entirely from circulating catecholamines and is not altered by chronic hypoxic incubation, as neither cholinergic blockade with atropine nor ganglionic blockade with hexamethonium altered baseline cardiovascular variables in N21 or H10 embryos. In addition, both atropine and hexamethonium injection did not alter the generally depressive effects of acute hypoxia -bradycardia and hypotension. However, H10 embryos showed significantly higher levels of noradrenaline and adrenaline at 70% of development, as well as higher noradrenaline at 80% of development, suggesting that circulating catecholamines reach maximal levels earlier in incubation for H10 embryos, compared to N21 embryos. Chronically elevated levels of catecholamines may alter the normal balance between α and β-adrenoreceptors in H10 alligator embryos, causing chronic bradycardia and hypotension of H10 embryos measured in normoxia.

Reduced egg shell permeability affects embryonic development and hatchling traits in Lycodon rufozonatum and Pelodiscus sinensis

“…Despite the difference in yolk utilization by embryos between the upper-half and bottom-half hypoxia treatments, regional hypoxia treatments produced smaller hatchlings compared to those of sham controls. Hypoxia inducing smaller hatchlings has also been reported in other reptile species (Eme et al 2011;Lungman & Piña 2013). Interestingly, the effect of regional hypoxia treatments on hatchling components showed between-species differences.…”

“…These results are consistent with some studies on the snapping turtle and alligator (Eme et al 2011(Eme et al , 2014), but inconsistent with other studies in turtles, crocodiles and birds showing decreased embryonic growth and survival induced by hypoxia (Snyder et al 1982;Seymour et al 1986;Kam 1993;Owerkowicz et al 2009;Nechaeva 2011). This discrepancy may reflect methodological differences in experimentally-induced hypoxia among studies.…”

Temperature-dependent sex determination modulates cardiovascular maturation in embryonic snapping turtles, Chelydra serpentina

“…Statistical analyses were conducted as described for similar parameters in American alligator embryos (Eme et al, 2011a;Eme et al, 2011b). Briefly, a two-way ANOVA was used to test for developmental changes (75% and 90% of incubation period) and sex differences in egg, embryo, liver and heart masses and resting P m and f H .…”

Embryonic common snapping turtles (Chelydra serpentina) preferentially regulate intracellular tissue pH during acid-base challenges

“…Exposure began at ∼18-22% of incubation (10-12 days post-laying, where 100% of incubation would correspond with hatch), determined by dissection of at least two representative embryos from each clutch as described previously (Crossley and Altimiras, 2005;Eme et al, 2011). For NC incubation, embryos were sealed inside large Ziploc bags, with two holes in the bag that allowed parallel inflow and outflow of gas in normoxic/normocapnic conditions in a walk-in Percival ® incubator (Percival Scientific, Perry, IA, USA).…”