Metabolic Effects Associated with Chronically Elevated Cortisol in Rainbow Trout (Oncorhynchus mykiss)

Abstract

Carbohydrate and protein metabolism were examined in rainbow trout, Oncorhynchus mykiss, fitted with mini-osmotic pumps which maintained plasma cortisol levels at approximately 100 or 200 ng∙mL⁻¹ for 10 d. Plasma glucose, lactate, and protein levels were unaffected by 10 d of cortisol administration, despite a significant elevation in plasma cortisol. Plasma amino acids in cortisol-treated fish (1023.8 ± 90.7 μg∙mL⁻¹) were significantly elevated compared with shams (716.7 ± 68.5 μg∙mL⁻¹) after 9 d. Liver glycogen content was significantly reduced by cortisol treatment. The activities of the liver enzymes assayed were unchanged; likewise the flux of radioactive substrates to radiolabeled CO₂, glucose, and protein in isolated hepatocytes was unaffected in trout with chronically elevated cortisol compared with shams. The glucose replacement rate (Ra) was unchanged after 2 wk of cortisol treatment. These data do not support the purported role of cortisol as a glucocorticoid in rainbow trout. While chronically elevated cortisol may increase the supply of plasma amino acids, the hormone does not appear to alter the manner in which this potential gluconeogenic substrate is metabolized. The absence of other stressors may be partially responsible for the differences between this study and others in the literature.