Figure 35.9: Effectiveness of Gonadotropin-Releasing Hormone (GnRH) Depends on a Pulsatile Pattern of Release In adult monkeys, GnRH is released from the hypothalamus in short pulses, about once every 1–3 hours. When the supply of GnRH is stopped (for example, by removing or destroying the hypothalamus), the anterior pituitary no longer secretes FSH or LH, and levels of these gonad-regulating hormones decline. Early studies in rhesus monkeys showed that in such cases FSH and LH production could be restored by injections of GnRH, but only if GnRH was delivered in pulses rather than continuously. The two patterns of GnRH delivery, however, also resulted in very different total doses of GnRH, complicating the interpretation of these initial results. The researchers did further experiments to determine whether delivery of GnRH in pulses is critical to its function in stimulating the secretion of FSH and LH.a