The study of GnRH control of reproductive function

The activity of the hypothalamic-pituitary-gonadal (HPG) axis is controlled by gonadotropin-releasing hormone (GnRH). GnRH, gonadotropins, and gonadal sex steroids are secreted in a pulsatile fashion. As the peripheral plasma concentrations of GnRH are too low for the existing assay systems, the pattern of pulsatile release of gonadotropins is often utilized for the indirect estimation of hypothalamic GnRH activity. In addition, the long-term pulsatile administration of exogenous GnRH in selected states of GnRH deficiency provides important information on the regulation of the HPG axis. Because of the limits of each approach, both investigational tools should be used complementary for the study of GnRH role in the control of pituitary and gonadal function. This article reviews recent information on GnRH physiology acquired with the use of these methods.