Changes in the cortisol dynamics of sockeye salmon ( Oncorhynchus nerka) resulting from secual maturation

Abstract

Maturing, mature, spawned, dexamethasone-injected, and gonadectomized salmon were injected with 0.5 μCi [4- 14C] cortisol. Blood samples were taken at various times after injection for determination of plasma dichloromethane-extractable radioactivity. The volume of distribution ( V 1 + V 2), biological half-life (T 3 2 ) , and metabolic clearance rates of the dichloromethane-extractable radioactivity were calculated on the basis of a two-compartment model V 1 increased from 4.7% in maturing fish to 19.0% in spawned fish ( p < 0.001). V 2 increased from 9.7% in maturing fish to 46.0% in spawned fish ( p < 0.001). The T 1 2 was 1.5 hr in maturing fish and 3.0 in spawned fish (0.05 < p < 0.001). Metabolic clearance rate increased from 20.5 ml/kg body wt/hr in maturing fish to 47.3 in spawned fish ( p < 0.01). Plasma cortisol concentration increased from 2.9 μg/100 ml in maturing fish to 8.5 in spawned fish. The data indicates that the secretion rate of cortisol is probably greater in the spawned than in the maturing fish. The secretion rate of cortisol was determined in one castrated, two mature, and one spawned salmon. When calculated on the basis of the resting cortisol concentration, the cortisol secretion rate varied from 0.7 μg/kg body wt/hr in the gonadectomized fish to 11.0 in the spawned fish. Injected [4- 14C]l cortisol was rapidly converted to cortisone. When [4- 14C]l cortisone was injected, there was no measurable conversion to cortisol.