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Summary.
Roosters were fed 0·1 % caffeine mixed by weight into a standard ration. With continued dietary caffeine administration, the average fertility of eggs collected for 2 weeks from untreated pullets inseminated with semen from the treated males at 0,7 and 14 days after the start of treatment was 30·8, 33·5 and 3·3 %, respectively. After 14 days of treatment fertility was significantly lower (P < 0·001) than before (0 days) or 7 days after treatment. Semen output and sperm concentration were markedly reduced 17-21 days after treatment, and no semen could be collected from the roosters after they had received caffeine for 30 days. Removal of dietary caffeine resulted in resumption of semen production and a return of fertility to the control level. Testicular histology showed that spermatocyte divisions ceased and spermiogenesis was abnormal, although Leydig tissue and the response of the males to massage for semen collection was not affected. The effects on spermatogenesis and fertility were reversible after treatment for 30 days.
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Prostaglandin F2α (PGF2α)-induced release of ovarian oxytocin was investigated to determine whether the effect in vivo was local. [3H]PGF2α infused downstream into a single ovarian lymphatic was transferred into the adjacent ovarian vasculature (estimated transfer 1.1 and 1.7%, two experiments). When unlabelled PGF2α was infused in a similar manner (76 pmol min−1), there was a prompt eightfold increase in ovarian oxytocin release from the adjacent ovary containing a corpus luteum, but no effect on the opposite corpus luteum, showing that the effect was local. Instillation of 2% lignocaine into the ovarian vascular pedicle did not affect PGF2α-induced oxytocin release, supporting the idea that neural mechanisms are not involved. Repeated doses of PGF2α given close-arterially produced a successive reduction in oxytocin release. This effect was prevented by a prior infusion of insulin-like growth factor-I (IGF-I), which itself gave a small, but significant, increase in oxytocin release. The results show that PGF2α in ovarian lymphatics acts locally and directly to stimulate ovarian oxytocin secretion, that repeated exposure of the corpus luteum to pulses of PGF2α can result in tachyphylaxis, and that this latter effect can be ameliorated by IGF-I infused in vivo.
