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M. Wilkinson and W. H. Moger

Summary. Pituitaries from immature male and female rats (5, 13, 21, 27 and 30 days of age) were removed at 08:00 or 16:00 h and stimulated with GnRH in vitro. In female rats more LH was released from pituitaries taken at 16:00 h than at 08:00 h on Days 21, 27 and 30, but not on Days 5 and 13. There were no differences in male rats in responsiveness of pituitaries taken at these two times. The ability of GnRH to induce release of more LH in the late afternoon may help to synchronize hormone output to coincide with first ovulation.

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W. H. Moger and O. O. Anakwe

Summary. Adrenergic antagonists were administered to rats by intratesticular injection at the time of unilateral orchidectomy and 5 h before autopsy, 24 h after surgery. Injections of the β-receptor antagonist dl-propranolol (0·5 or 1·0 mg/injection) significantly inhibited the increase in the concentration of androgens in testicular vein plasma or interstitial fluid that occurred in unilaterally orchidectomized animals injected with vehicle. dl-Propranolol injections in animals with both testes did not reduce testicular or peripheral androgen concentrations or their increase after hCG administration. Injections of the less potent isomer (+)-propranolol or the α-receptor antagonist phentolamine did not inhibit the response to unilateral orchidectomy. It is concluded that the compensatory increase in androgen secretion induced by unilateral orchidectomy is, at least in part, the result of β-adrenergic stimulation of steroidogenesis.

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B. D. Fantie, R. E. Brown, and W. H. Moger

Summary. Adult male Long-Evans rats (90 days of age) were housed in 12 h light:12 h dark (Group LD), constant white light (Group LL), or constant dark (dim red light) (Group DD) for 60–90 days. The first of two sexual behaviour tests revealed that more (P < 0·05) rats in Group LD achieved intromission than did those in Groups LL and DD. Only 33% of Group LL and 32% of Group DD rats ejaculated. In contrast, all Group LD rats that mounted eventually ejaculated. Males in Group LD achieved more (P < 0·05) ejaculations (mean of both tests combined, 3·4) than did males in Groups LL (1 ·5) or DD (1·2). Although there were no notable differences amongst the groups in the weights of the accessory sex organs, males in Group DD had higher (P < 0·05) serum androgen levels than did those in Groups LL and LD while Group LL males had higher (P < 0·05) serum prolactin levels than did those in Groups LD and DD. There were no differences in LH or FSH levels. In addition, more rats in Group LL had disrupted activity rhythms than did Group DD rats. These results indicate that housing in constant white or dim red light disrupts sexual behaviour in male rats and may do so through different neuroendocrine mechanisms.