Gonadal hormone feedback on pituitary gonadotropin genes.
The pituitary gonadotropins LH and FSH, which act on the ovaries and testes to promote gametogenesis and sex steroid production, are regulated 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 effects 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 pituitary cells to alter FSH synthesis specifically, with no effects on LH. Changes in gonadotropin subunit gene transcription and mRNA levels occur very rapidly and have profound effects on physiological levels of the hormones. In this article, the effects of the gonadal steroids and peptides as modifiers of the rat gonadotropin genes in a subunit specific manner are reviewed, and the physiological implications discussed.
Shupnik
M A
MA
Division of Endocrinology and Metabolism, Department of Internal Medicine, Department of Physiology, University of Virginia Health Sciences Center, Charlottesville, VA, USA.