The influence of mating and related stimuli on plasma levels of luteinizing hormone, follicle stimulating hormone, prolactin, and testosterone in the male rat

Male rats were exposed to several stimuli associated with mating, and their resting levels of LH, prolactin (PRL), and testosterone (T) were compared to their hormone levels after stimulation. Sexually experienced rats showed two-to fourfold increases in levels of these hormones after both mating with estrous females and attempting to mate with unreceptive females. Only LH levels were significantly elevated by the odor of estrous females or by non-tactile contact with estrous females. Neither transfer to an empty mating arena nor interaction with another male altered the rats’ hormone levels. The LH and PRL levels of sexually naive rats showed a similar pattern of response, but T levels in naive rats were unaffected by all stimuli including mating. In a further study, rats were killed immediately after mating for varying times up to 1 h, and their levels of LH, FSH, PRL, and T were measured. Both LH and PRL levels peaked 5 min after the start of mating and the declined, while FSH levels remained unchanged. T levels rose slowly and were significantly elevated only after an hour of mating. These results show that levels of LH and PRL, but not FSH, are increased during mating in the male rat, and suggest that the increase in T levels may be due to the prior increase in LH and PRL levels. Furthermore, the rapidity of the rise in LH and PRL levels, coupled with the consistent response of these hormones to unsuccessful attempts to mate, suggests that rather than following mating, the increases in LH and PRL may precede it.