Effect of seminal oestrogens of the boar on prostaglandin F2α release from the uterus of the sow

Abstract Boar semen is rich in oestrogens which lead to an increase of the myometrial contraction frequency in the sow at day 0 (onset of standing heat). To clarify whether this effect is mediated by an endometrial release of prostaglandin F 2α (PGF 2α ) two experiments were carried out. 1. (1) Transcervical intrauterine infusion of 10 μg oestradiol in 100 ml saline led to an increase of PGF 2α in utero-ovarian vein plasma of three chronically cannulated sows within 2 min. Elevated concentrations were measured for 40 min. The maximum at 6 min was 4-fold compared to the period before infusion. Oestrone-sulphate (10 μg in 100 ml saline) led to a minor rise (2.5-fold) for only 10 min, saline alone had no effect. 2. (2) Measurements of the PGF 2α metabolite (PGFM) in peripheral plasma of other sows were carried out for a systematic evaluation. No apparent change was found over a 6-h period in sows which were not infused (controls, n = 7). Both infusion of saline (100 ml, n = 7) and saline with oestrone (10 μg, n = 6) 1 h after the onset of sampling led to only a slight increase during the first hour after treatment (saline 0.79 vs. 1.17 ng/ml, P ≤ 0.01; oestrone 0.78 vs. 0.99 ng/ml, P ≤ 0.01) due to mechanical stimulation. Oestrone-sulphate (10 μg, n = 6) increased the concentrations 2-fold (0.92 vs. 2.2 ng/ml, P ≤ 0.01). The increase was paralleled by a peripheral increase in oestrone-sulphate concentrations. Both the infusion of oestradiol (10 μg, n = 5) and mating ( n = 6) led to a pronounced peripheral rise of PGFM which was up to 3.5-fold ( P ≤ 0.001) after oestradiol and up to 2.5-fold ( P ≤ 0.001) after mating when compared to the control period. Both patterns of increased PGFM concentrations were reflected by a similar course of oestradiol concentrations in peripheral plasma. Mating led to a biphasic release of PGFM (2.7 ng/ml at 10 min, 2.6 ng/ml at 80 min) and also a biphasic pattern of peripheral oestradiol was measured. This biphasic course is explained by an immediate effect of seminal plasma oestrogens and a later effect of oestrogens which are bound to the sperm surface. It is concluded that oestrogens lead to a release of PGF 2α from the endometrium. This release explains an increase of the contraction frequency reported earlier.