Dynamics of Cortisone Secretion in Sockeye Salmon (Oncorhynchus nerka) during Sexual Maturation and after Gonadectomy

Abstract

Indices of cortisone secretion in sockeye salmon (Oncorhynchus nerka) were determined by monitoring the disappearance of labelled cortisone in plasma after the injection of a single dose of 4-14C-cortisone. Cortisone concentrations were determined by a protein-binding method.The volume of distribution in the inner (V1) and outer (V2) pool, biological half-life [Formula: see text], metabolic clearance rate (MCR), plasma concentration, and secretion rate of cortisone increased with sexual maturation, except cortisone concentration in males during anaesthetic stress. Differences between sexually immature fish and fish matured in captivity were generally significant (P < 0.05). After gonadectomy of mature fish the return of many of these indices to the levels of immature fish was noted. With some exceptions the changes observed resembled qualitatively those of cortisol dynamics. In sexually mature and spawned fish, cortisone concentrations and secretion rates, did not increase during anaesthetic stress in contrast to those of cortisol, suggesting that the full capacity of the cortisone secretion mechanism had already been reached in the resting state.Cortisone secretion rates were similar in magnitude to those of cortisol in resting fish, but cortisol secretion rates were two to four times higher than those of cortisone during anaesthetic stress.