The adrenal gland of stranded whales ( Kogia breviceps and Mesoplodon europaeus): In vitro modulation of mitochondrial steroid enzyme activities

The effects of adrenocorticotropic hormone (ACTH), cyclic AMP (cAMP), NADPH, Krebs cycle intermediates (KCI), and metyrapone on the two key mitochondrial reactions in the biosynthesis of glucocorticoids—11β-hydroxylation and cholesterol cleavage—were studied in preparations from the adrenal glands of stranded whales ( Kogia breviceps and Mesoplodon europaeus) and some terrestrial mammals. ACTH (30 p M) and cAMP (1.0 m M) enhanced the 11β-hydroxylation of [11- 3H]deoxycorticosterone ([ 3H]DOC) in monolayer cultures of whale adrenal cells during a 4-hr incubation period. Mitochondria from whale and beef adrenals responded in a similar dose-related fashion to NADPH generated by the addition of increasing amounts of NADP (0–0.6 m M) to the in vitro system; at each level of NADPH, 11β-hydroxylation of [ 14C]DOC was several-fold greater than the cleavage of [ 14C]cholesterol. Metyrapone interfered in a dose-related manner with both the 11β-hydroxylation of [ 14C]DOC and the cleavage of [ 14C]cholesterol by mitochondria from whale and beef adrenals; inhibition of 11β-hydroxylation exceeded 60% at 0.1 m M metyrapone and was virtually complete at 1.0 m M in both species, while inhibition of [ 14C]cholesterol cleavage averaged 25% at 0.1 m M metyrapone and 50% at 1.0 m M. The effect of exogenous NADPH in supporting the 11β-hydroxylation of [ 14C]DOC could be maintained in beef and rat adrenal mitochondria to the extent of 70–100% by substitution with any of the KCI. This phenomenon was not found in similar whale studies where the KCI were all ineffective. This finding represents the major biochemical difference between adrenal steroidogenesis in whales and in terrestrial mammals, but it is not clear whether this distinction represents a physiologic adaptation to the aquatic environment or an effect of the unknown pathologic process associated with the stranding of these marine mammals.