Secretion of Luteinizing Hormone in Male Mice: Factors that Influence Release during Sexual Encounters*

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Abstract
These experiments represent a search for factors that influence the secretion of LH in male mice during sexual encounters. Sequential changes in blood levels of LH were monitored in cannulated tethered males during their exposure to estrous females, ovariectomized females, urine pooled from all stages of the estrous cycle, or appropriate control conditions. Males that experienced spontaneous episodic LH release immediately before external stimulation did not secrete LH in response to any of the female stimulus conditions. Otherwise, the initial reaction to estrous females, ovariectomized females, and urine was an identical acute release of LH that typically returned to baseline in 45 min. Males that ejaculated 25 min or more after their initial LH response also experienced a second surge of hormone release, but males ejaculating before that time did not surge twice. A second exposure to urine 50 min after the first exposure yielded no LH response. These results suggest that the pattern of LH secretion in a male mouse during a sexual encounter is dependent upon at least two stimulatory and two inhibitory factors. Two distinct stimuli, a urinary pheromone that is common to both receptive and nonreceptive females and a stimulus that is specifically associated with either intromission or ejaculation, cause the release of LH in an all or none manner. The response to these stimuli can be antagonized, however, either by a refractory period that follows the release of LH or by habituation to the urinary cue. The refractory period, in turn, can be initiated by either the socially induced release of LH or a spontaneous episodic release of LH. (Endocrinology 106: 1224, 1980)