The role of luteal oxytocin in episodic secretion of prostaglandin F2alpha at luteolysis in the ewe

摘要

On day 10 of the oestrous cycle, Dorset ewes underwent surgical removal of the corpora lutea (lutectomy; n = 4) or sham operation (sham; n = 4). Lutectomized ewes were administered progesterone by twice daily i.m. injection in corn oil (20 mg/day) until day 14 when treatment was ceased to simulate luteolysis. The concentration of 13, 14 dihydro-15-keto PGF2alpha (PGFM) was measured in peripheral blood samples collected at 20-min intervals for 8 h on days 12-16 of the cycle. Progesterone and oestradiol concentrations were similar in the 2 groups over the whole experimental cycle while oxytocin decreased (P<0.01) following lutectomy. No PGFM release episodes were seen on day 12 or 13, while from days 14-16 both groups exhibited a similar episode frequency (lutectomy 0.9/ewe/8 h; sham 0.8/ewe/8 h). Analysis of episode characteristics revealed lower (P<0.05) episode amplitude but longer (P<0.05) episode duration in the lutectomy group. It is concluded that a normal frequency of PGFM release episodesoccurs independently of luteal oxytocin secretion. However, luteal oxytocin is involved in regulating the pattern of release, perhaps causing the release of episodes of the magnitude required for the successful completion of luteolysis.