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Unilateral control of ovarian oxytocin release and the facilitatory effects of insulin-like growth factor-I in sheep

Prostaglandin F₂ (PGF₂)-induced release of ovarian oxytocin was investigated to determine whether the effect in vivo was local. [³H]PGF₂ 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 PGF₂ 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 PGF₂-induced oxytocin release, supporting the idea that neural mechanisms are not involved. Repeated doses of PGF₂ 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 PGF₂ in ovarian lymphatics acts locally and directly to stimulate ovarian oxytocin secretion, that repeated exposure of the corpus luteum to pulses of PGF₂ can result in tachyphylaxis, and that this latter effect can be ameliorated by IGF-I infused in vivo.

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				J. A. McCracken, E. E. Custer, and J. C. Lamsa Luteolysis: A Neuroendocrine-Mediated Event Physiol Rev, April 1, 1999; 79(2): 263 - 323. [Abstract] [Full Text] [PDF]