EFFECTS OF ESTROGEN ON GLUCONEOGENESIS AND RELATED PARAMETERS IN MALERAINBOW-TROUT

To investigate the effects of estrogen, the hormone responsible for vi tellogenesis, on gluconeogenesis, male rainbow trout were implanted wi th 17beta-estradiol or given a sham procedure. Plasma glucose concentr ation in estrogenized fish was 50% of the control fish (6.4 mM). Gluco se synthesis from physiological concentrations of alanine was 0.08 mum ol.g cells-1.h-1 compared with 0.20 mumol.g cells-1.h-1 in control fis h; 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. Glu coneogenesis from 5 mM lactate was also significantly depressed in imp lanted fish. Oxidation of alanine, serine, and lactate was not signifi cantly affected by estrogen implantation. The maximium clearance veloc ity of a key enzyme negatively regulating gluconeogenesis, pyruvate ki nase, was 3.03 mumol.g cells-1.h-1 in estrogen (E2) implanted fish com pared with 7.83 mumol.g cells-1.h-1 in control fish. No significant di fferences in plasma insulin or glucagon were found in the two groups. We conclude that estrogen depresses gluconeogenesis and that this redu ction contributes to the lower plasma glucose concentration seen in vi tellogenic trout.