The pituitary--adrenal axis in the sea snake, Hydrophis cyanocinctus daudin.

The sea snake Hydrophis cyanocintus was subjected to conventional pharmacological tests of pituitary-adrenal function. Administration of synthetic ACTH resulted in adrenal hypertrophy, enhanced Δ⁵-3β-hydroxysteroid dehydrogenase (3β-OHSD) activity and raised peripheral titres of corticosterone and aldosterone to 300% those of controls. Metopirone treatment resulted in adrenal hyperplasia and enhanced 3β-OHSD activity, but aldosterone titres were unchanged despite a 90% reduction in corticosterone titre. Dexamethasone administration was followed by adrenal atrophy and diminished 3β-OHSD activity. Titres of both corticosteroids were much lowered. Despite such marked variations in adrenal function, no alteration in plasma ion concentrations or total osmolarity could be detected. These and earlier data suggest that separate regulatory mechanisms for corticosterone and aldosterone may exist in the sea snake, and such a differential regulation may be of physiological importance.