STEROID ACTIVATION OF THE BRAIN-PITUITARY COMPLEX GONADOTROPIC FUNCTION IN THE TRIPLOID RAINBOW-TROUT ONCORHYNCHUS-MYKISS

Testosterone and estradiol were implanted into triploid rainbow trout, and their effects on brain and pituitary salmon gonadotropin-releasin g hormone (sGnRH) content and on gonadotropin (GtH2) levels in the pit uitary and blood were studied. In the hypothalamic areas, neither ster oid altered sGnRH content. In the brain tissues (ventral telencephalon and preoptic areas), testosterone (0.5 mg/kg BW) significantly increa sed sGnRH contents and larger doses induced a more rapid increase. Est radiol induced a similar increase which occurred later than the respon se to the same dose of testosterone. Both steroids also stimulated pit uitary sGnRH, with estradiol being less potent. Only testosterone indu ced long-term increases in plasma GtH2 content. Both steroids may act on the synthesis and release of GnRH, with testosterone having a great er influence on the control of gonadotropin secretion, especially at t he end of the cycle. (C) 1996 Academic Press, Inc.