Episodic release of luteinizing hormone in male mice: antagonism by a neural refractory period.

A refractory period of LH secretion follows both an internally generated and a female-induced, episodic release of LH in male mice. These experiments examined the duration of the refractory period and investigated its physiological basis. Plasma LH was measured in sequential blood samples that were withdrawn from chronically cannulated male mice. The males were exposed to two successive stimuli that were presented at 10-, 25-, or 45-min intervals; the two stimuli were a female both times, LHRH both times, or LHRH first and a female second. Males that were exposed to two successive females released LH in response to the second female only if 45 min had elapsed between exposures. All males in the LHRH-LHRH treatment group released LH after both injections of LHRH at all three stimulus intervals. The female stimulus evoked LH secretion in the LHRH-female treatment group at all three times after LHRH administration. In a second set of experiments, testosterone capsules that maintained the seminal vesicle weights of castrated males at well above normal levels did not block their LH responses to a female stimulus. When taken together, these results indicate that a refractory period lasting between 25 and 45 min follows episodes of LH release that are socially generated, that this refractory period has its basis in altered neural rather than pituitary activity and, finally, that this neurally based refractory period is not a result of inhibitory hormonal feedback.