Gonadotropin secretion does not follow the GnRH input signal exactly, particularly when GnRH is administered in a nonphysiologic pattern. Soon after GnRH became available for experimental use, researchers noted that continuous administration of this hormone (e.g., by constant intravenous infusion) did not lead to constant LH output but rather to a biphasic pattern of increase, implying that two pools of releasable hormone existed.31 After the maximal response, a decline was seen in LH responsiveness that could not be explained by gonadal inhibitory feedback.32 Pulsatile administration of GnRH was observed to cause persistent pulsatile secretion of LH, whereas continuous GnRH infusion caused a desensitization of pituitary responsiveness.33 Continuous high-dose administration of GnRH over several days leads to almost complete failure of the ability of the pituitary to respond to GnRH secreted endogenously, yielding an experimentally induced hypogonadotropic hypogonadal state.34