Evidence for the pulsatile release of PGF-2  inducing the release of ovarian oxytocin during luteolysis in the ewe

Abstract

Frequent blood samples were removed from a utero-ovarian vein, a jugular vein and a femoral artery of 5 ewes during luteolysis. Analysis of these samples for oxytocin-associated neurophysin revealed a significant venous-arterial difference across the ovary and uterus but not across the head. This occurred during the pulsatile surges as well as when levels were basal and confirms the corpus luteum as a major source of the pulsatile surges of oxytocin-associated neurophysin and oxytocin that occur during CL regression and also of the elevated luteal phase concentrations of both hormones. The pulsatile surges of oxytocin-associated neurophysin measured in the utero-ovarian vein were accompanied by the release of an approximately equimolar amount of oxytocin. The concentration of PGF-2 alpha in the utero-ovarian vein samples began to increase before the levels of oxytocin and oxytocin-associated neurophysin started to increase. This suggests that uterine PGF-2 alpha initiates the release of ovarian oxytocin and oxytocin-associated neurophysin during luteolysis in the ewe.

Components of a platelet-activating factor-signaling loop are assembled in the ovine endometrium late in the estrous cycle

“…Thus the onset of endometrial PAF production and PAF receptor expression under the influence of estradiol and progesterone may allow the production of low-amplitude PGF 2␣ release to commence from day 12 or day 14. It is known that low-amplitude PGF 2␣ pulses normally precede and induce the release of oxytocin (18,23), and it was proposed that the action of the released oxytocin on the PAF-primed endometrium might cause the substantive release of luteolytic PGF 2␣ (4). The proposed model may incorporate the action of anti-luteolytic effects of pregnancy, because it was shown that the embryonic anti-luteolysin interferoninhibited both PAF-induced PGFM pulses and the synergism between PAF and oxytocin (4).…”

“…The oxytocin receptor is expressed in the luminal epithelium, caruncular stroma, and deep glands of the endometrium (27,40) and is regulated by the presence of estradiol (10). Oxytocin, acting via its endometrial receptor, induces the release of PGF 2␣ (23). Furthermore, PGF 2␣ can act on its receptor in the corpus luteum to induce the release of oxytocin (23).…”

“…Oxytocin, acting via its endometrial receptor, induces the release of PGF 2␣ (23). Furthermore, PGF 2␣ can act on its receptor in the corpus luteum to induce the release of oxytocin (23). It was postulated that a positive feedback loop exists between these two events (9).…”

In Vivo Oxytocin Release from Microdialyzed Bovine Corpora Lutea During Spontaneous and Prostaglandin-Induced Regression

“…A related experiment demonstrated the ability of ovine corpora lutea to undergo PGF 2␣ -induced luteolysis despite Ͼ 95% depletion of luteal oxytocin stores [4]. Although these experiments provide evidence that absence of luteal oxytocin release does not alter the luteolytic process, other researchers have demonstrated the concurrent release of luteal oxytocin and uterine prostaglandin in vivo in sheep [5].…”

Effect of systemic intravenous infusion of PGF-2 and 13,14-dihydro-15-keto-PGF-2 on the release of oxytocin-associated neurophysin from the ovary in the ewe

“…Oxytocin-neurophysin, progesterone and PGFM were measured as described previously (Fairclough & Payne, 1975;Moore & Watkins, 1983;Moore et al, 1986). The oxytocin-neurophysin radioimmuno¬ assay (RIA) recognizes equally ovine neurophysin II and its putative metabolite, ovine neurophysin I (Moore & Watkins, 1981), and has a cross-reactivity of 2-5% with the ovine vasopressin neurophysin, neurophysin-III.…”