Secretory dynamics of 1 alpha-hydroxycorticosterone in the elasmobranch fish, Scyliorhinus canicula.

Peripheral plasma concentrations, metabolic clearance rates (MCR) and blood production rates (BPR) of 1 alpha-hydroxycorticosterone (1-OH-B) were determined in female dogfish (Scyliorhinus canicula) under varying environmental conditions. The constant-infusion technique, using high specific activity tritiated 1-OH-B, was applied to measure the MCR, and BPR were derived from the product of plasma concentration and MCR at equilibrium. Urea plasma clearances and apparent BPR were assessed in a similar manner. Fish were adapted stepwise to 140, 120, 90, 80, 70, 60 and 50% normal sea water (about 1000 mosmol/l). In all cases 1-OH-B was the major corticosteroid, cortisol and corticosterone were sought but never detected. In environments of reduced osmolarity, plasma osmolarity, sodium, chloride and urea concentrations all declined, alongside increases in plasma concentrations, MCR and BPR of 1-OH-B. In fish held in environments at concentrations greater than normal sea water, plasma osmolarity, sodium, chloride and urea concentrations all increased. Plasma clearance of urea increased in fish held in environments more dilute than sea water, while it decreased in the more hyperosmotic waters. It is tentatively concluded that homeostasis of plasma composition, with particular respect to urea, is in part regulated by 1-OH-B in the dogfish.