Regulation of gonadotropin-releasing hormone in nonhypothalamic tissues

It is well established that hypothalamic gonadotropin-releasing hormone (GnRH) controls reproductive function by stimulating the production of gonadotropins from the pituitary. GNRH gene and its receptor (GnRHR) have also been detected outside the hypothalamus, and a growing body of literature supports an extrapituitary role for GnRH action. The exact function of GnRH in these tissues is not known, but GnRH expression has been described in reproductive tissues, including the ovary, placenta, breast, testes, and prostate. This article provides an overview of the regulation of GnRH gene expression in nonhypothalamic reproductive tissues. After GnRH gene structure is reviewed, the physiologic role of GnRH and regulation of its expression in several reproductive tissues are examined. When possible, transcriptional regulation is discussed, but due to low levels of expression, transcriptional regulation of GnRH in extrahypothalamic tissues has been extremely difficult to study. Consequently, the factors that mediate GnRH gene expression in these tissues are only beginning to be identified.