Neurotransmitters and lymphatic-vascular transfer of prostaglandin F2α stimulate ovarian oxytocin output in sheep

Abstract

The mechanisms of lymphatic-vascular transfer across the ovarian vascular pedicle were studied in anaesthetized sheep 8–15 days after ovulation. [³H]Prostaglandin F_2α (PGF_2α), [¹⁴C]mannitol and [³⁶Cl]Na were infused continuously into either a uterine lymphatic or a uterine vein and the kinetics of transfer into the adjacent utero-ovarian vein or ovarian plasma were studied. Transfer occurred according to the sequence [³⁶Cl] > [¹⁴C] > [³H] indicating that PGF_2α is not transferred by rapid diffusion, as with [³⁶Cl]Na, nor by a paracellular route, as with [¹⁴C]mannitol, but by a slower process probably involving facilitated diffusion. Transfer into the adjacent utero-ovarian vein or ovarian blood was greater when compounds were infused into a uterine lymphatic than into a uterine vein. Substantially more [³H]PGF_2α occurred in the adjacent corpus luteum than either of the other compounds after a lymphatic infusion. Intra-lymphatic infusion of PGF_2α stimulated the release of ovarian oxytocin but the effect was not confined to the adjacent ovary. Intravenous (jugular) infusion of PGF_2α failed to stimulate ovarian oxytocin secretion whereas close-arterial infusion into the ovaries was effective, and the possibility was investigated that any systemic effect of PGF_2α was mediated through neural mechanisms. Noradrenaline and acetylcholine were both effective in causing the release of ovarian oxytocin when infused close-arterially into the ovary. With infusions of acetylcholine, ovarian oxytocin secretion rate was increased over fivefold without any change in posterior pituitary release. Noradrenaline and acetylcholine produced a concomitant fall in ovarian blood flow, and neurotransmitter-induced ischaemia may have played a role in ovarian oxytocin release. The finding that PGF_2α infused into a uterine lymphatic stimulates ovarian secretion of oxytocin, and that the effect is bilateral whereas PGF_2α accumulation in ovarian tissue is unilateral, implies that its mechanism of action may not be solely directed at the luteal cell. Journal of Endocrinology (1989) 122, 147–159