Summary. Pregnant (N = 10) and non-pregnant (N = 10) ewes were bled every 2 h from Days 12 to 17 after oestrus (oestrus = Day 0). Plasma concentrations of progesterone, 15-keto-13,14-dihydro-PGF-2α and 11-ketotetranor-PGF metabolites were determined in all samples. The number of PGF-2α pulses in non-pregnant ewes was 8·2 ± 0·4 (mean ± s.e.m.) with an interpulse interval of 10·7 ± 0·7 h. Two or 3 pulses of low frequency (interpulse interval = 13·4 ± 1·6 h) occurred in most non-pregnant ewes before the onset of luteolysis; the interpulse interval then decreased to 7·9 ± 0·4 h for the 6·0 ± 0·3 pulses temporally associated with luteolysis. In contrast, the number of PGF-2α pulses in pregnant ewes was lower (2·5 ± 0·7, 0–8) and the interpulse intervals longer (18·9 ± 6·1 h). Most pulses occurred on Days 14 and 15 in the pregnant and non-pregnant ewes.
The mean concentrations of both PGF-2α metabolites in non-pregnant ewes were highest on Day 15 while basal levels of both metabolites remained constant at all times. In pregnant ewes, the mean concentrations of both metabolites were highest on Day 14; basal concentrations of both metabolites were also highest on Day 14. The mean concentrations of 15-keto-13,14-dihydro-PGF-2α were higher in pregnant than in non-pregnant ewes on Days 13 and 14 (P < 0·05) and higher in non-pregnant than pregnant ewes on Day 15 (P < 0·05). The basal concentrations of the 15-keto metabolite were higher in pregnant than non-pregnant ewes at Days 13, 14, 15, 16 and 17 (P < 0·05). Both the mean and the basal concentrations of 11-ketotetranor-PGF metabolites were higher in pregnant than in non-pregnant ewes on Day 14 (P < 0·05).
It is concluded that uterine production of PGF-2α peaks at Days 14–15 after oestrus in pregnant and non-pregnant ewes. Patterns of release differ, however, in that non-pregnant ewes have a pulsatile PGF-2α pattern superimposed on a constant baseline, while pregnant ewes have an increasing basal secretory pattern which is more nearly continuous, i.e. not pulsatile in form. Modification of pulsatile PGF-2α synthesis and release is therefore a key aspect of prolongation of luteal function at the beginning of pregnancy in the ewe.
Keywords: PGF-2α; sheep; pregnancy