Effect of the level of oestradiol on oxytocin-induced prostaglandin F2 alpha release in the cow.
We have investigated the effects of oestradiol-17 beta on the development of the luteolytic signal (prostaglandin F2 alpha (PGF2 alpha) release to an oxytocin challenge) using a steroid-treated ovariectomised cow model. Long-term ovariectomised cows were pre-treated with progesterone for 14 days followed by oestradiol-17 beta for 2 days to induce oestrus (day 0), and were then treated for a further 16 days with physiological doses of progesterone and oestradiol-17 beta to simulate a luteal phase. On day 11 oestradiol was either withdrawn (low group; n = 4), maintained (normal group; n = 4) or increased (high group; n = 4), generating mean (+/- S.E.M.) plasma concentrations of oestradiol from days 12-16 of 0.9 +/- 0.1, 2.3 +/- 0.4 and 3.7 +/- 0.2 pg/ml respectively. Basal and oxytocin-stimulated PGF2 alpha secretion was monitored by measuring concentrations of the principal metabolite of PGF2 alpha, 13,14-dihydro-15-keto PGF2 alpha (PGFM), in plasma samples collected before and after daily i.v. injection of 50 IU oxytocin from days 12-16. Basal PGFM was unaffected by the level of oestradiol treatment. In the normal group significant rises in plasma PGFM were seen following oxytocin on days 12, 13 and 14 (P < 0.05) as well as days 15 and 16 (P < 0.01). In the low group significant elevations in PGFM were only seen on days 15 and 16 (P<0.05), and were smaller (P<0.05) than those seen in the normal group.(ABSTRACT TRUNCATED AT 250 WORDS)
Mann
G E
GE
Department of Physiology and Environmental Science, University of Nottingham, Sutton Bonington, Leicestershire, UK.
Lamming
G E
GE
D000818:Animals; D002417:Cattle / Q000097:blood*; D015237:Dinoprost / Q000097:blood*; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D005260:Female; D010052:Ovariectomy; D010121:Oxytocin / Q000494:pharmacology*; D011374:Progesterone / Q000097:blood / Q000494:pharmacology
D011374:Progesterone; D004958:Estradiol; D010121:Oxytocin; D015237:Dinoprost