GONADAL HORMONE FEEDBACK ON PITUITARY GONADOTROPIN GENES

The pituitary gonadotropins LH and FSH, which act on the ovaries and t estes to promote gametogenesis and sex steroid production, are regulat ed by changes in the levels of steroids and gonadal peptides. Steroid feedback can be positive, as demonstrated by the estrogen and LH surge at ovulation, or negative, as demonstrated by the rise in LH and FSH after gonadectomy or reductions in steroid synthesis. Modulatory effec ts of the steroids estrogen and testosterone may be mediated directly at the level of-the pituitary cells, or by alterations in the release of the hypothalamic releasing factor GnRH. Gonadal peptides, including activin and inhibin, have been shown to have direct effects on pituit ary cells to alter FSH synthesis specifically, with no effects on LH. Changes in gonadotropin subunit gene transcription and mRNA levels occ ur very rapidly and have profound effects on physiological levels of t he hormones. In this article, the effects of the gonadal steroids and peptides as modifiers of the rat gonadotropin genes in a subunit speci fic manner are reviewed, and the physiological implications discussed. (C) 1996, H.A. Shupnik