EFFECTS OF ESTROGEN ON GLUCONEOGENESIS AND RELATED PARAMETERS IN MALE RAINBOW-TROUT

To investigate the effects of estrogen, the hormone responsible for vitellogenesis, on gluconeogenesis, male rainbow trout were implanted with 17beta-estradiol or given a sham procedure. Plasma glucose concentration in estrogenized fish was 50% of the control fish (6.4 mM). Glucose synthesis from physiological concentrations of alanine was 0.08 mumol.g cells-1.h-1 compared with 0.20 mumol.g cells-1.h-1 in control fish; synthesis from physiological concentrations of lactate was reduced by over 50% (0.88 vs. 0.36 mumol.g cells-1.h-1) in implanted fish. Gluconeogenesis from 5 mM lactate was also significantly depressed in implanted fish. Oxidation of alanine, serine, and lactate was not significantly affected by estrogen implantation. The maximium clearance velocity of a key enzyme negatively regulating gluconeogenesis, pyruvate kinase, was 3.03 mumol.g cells-1.h-1 in estrogen (E2) implanted fish compared with 7.83 mumol.g cells-1.h-1 in control fish. No significant differences in plasma insulin or glucagon were found in the two groups. We conclude that estrogen depresses gluconeogenesis and that this reduction contributes to the lower plasma glucose concentration seen in vitellogenic trout.