Evidence that acute stress inhibits ovarian steroidogenesis in rainbow trout in vivo, through the action of cortisol.

Sexually mature (preovulatory) rainbow trout exposed to confinement stress showed a transitory increase in plasma cortisol levels that was accompanied by a similarly brief depression in plasma testosterone (T) levels. Plasma levels of maturational gonadotropin (GtH) and 17beta-estradiol (E(2)) were unaffected by stress. A similar pattern was displayed by fish exposed to stress in midvitellogenesis. Treatment of vitellogenic fish with exogenous cortisol resulted in significant increases in plasma cortisol at 1 and 3 h postinjection (p.i.). This was associated with significant depression of plasma T levels at 1 and 3 h p.i. and plasma E(2) levels at 3 and 6 h p.i. Plasma levels of GtH were unaffected by treatment with cortisol. Treatment of fish at an earlier stage of vitellogenesis with two different doses of cortisol resulted in very high elevations of plasma cortisol, but no effect on plasma levels of E(2) or GtH. In contrast, plasma T levels showed a stepwise decline over time. These results suggest that the inhibitory effects of stress on reproduction are mediated by cortisol and that the effect does not involve inhibition of GtH secretion and possibly acts at the level of GtH signal-transduction. Copyright 2000 Academic Press.