Cortisol Secretion Rate in Gonadectomized Female Sockeye Salmon (Oncorhynchus nerka): Effects of Estrogen and Cortisol Treatment

Abstract

Gonadectomized female sockeye salmon (Oncorhynchus nerka) were injected intramuscularly with cortisol, estradiol, estradiol cypionate, or peanut oil for 8 weeks. The metabolic clearance rate of cortisol was determined by the single injection technique and calculated from the formula for a two pool system. The cortisol secretion rate was determined from the metabolic clearance rate and the plasma cortisol concentration.The volume of distribution of cortisol in the inner compartment (V1) and the outer compartment (V2), the metabolic clearance rate (MCR), the resting secretion rate (S), and the resting plasma cortisol concentration were all significantly higher in the estradiol-injected group than in the peanut oil-injected control group, and the plasma cortisol concentration at the end of the experiment was lower. V1, MCR, and S were also significantly higher in the estradiol cypionate-injected group. There were no significant differences between the cortisol-injected group and the peanut oil-injected control group or in the biological half life of cortisol between any groups.There were no significant changes in the red colour of the flesh or in body weight during the experiment. However, the cortisol-injected group did show the largest weight loss.