Spontaneous electromyographic activity throughout the cycle in the sow and its change by intrauterine oestrogen infusion during oestrus

Abstract

Two experiments were carried out to monitor influences on the uterine electromyographic activity (EMG) in cyclic gilts with chronic uterine EMG electrodes. In Exp. 1 the EMG was recorded continuously from Day - 1 for 24 days and was evaluated for frequency, duration and amplitude. Progesterone and oestradiol in peripheral plasma were measured daily. As high amounts of oestrogens are characteristic for boar semen, in Exp. 2 the influence of seminal oestrogens on uterine contractions at Day 0 (first day of standing reflex) was investigated in gilts with chronic intrauterine catheters. They were infused with 10 ml saline (N = 4) or saline with physiological amounts of oestrogens (5 μg oestradiol + 2 μg oestrone + 4.5 μg oestrone sulphate; N = 4). Sham-treated gilts (infusion catheters, no infusion; N = 5) served as controls. The EMG was recorded for 2 h before and 9 h after infusion. In Exp. 1 the maximal amplitude (2040 ± 98 μV) and duration (32 ± 1.7 sec) but the lowest frequency (15.8 ± 2.1 contractions/h) were found on Day 0. With decreasing oestrogen and increasing progesterone concentrations the frequency increased continuously until Day 5 (63.5 ± 1.0 contractions/h) while the amplitude (183 ± 13 μV) and duration (3.3 ± 0.7 sec) decreased. During Days 6-13 the EMG activity was not detectable. The reverse pattern was found from the onset of luteolysis until the following Day 0. On Day 0 a significant correlation between oestradiol and the duration (r = 0.81; P < 0.01; n = 10) but not the frequency was observed. In Exp. 2 no significant change in contractile activity was found for the saline-infused group and the controls over the 11-h recording periods. After infusion of saline with oestrogens the frequency increased significantly (P < 0.001) from 14.0 ± 3.1 contractions/h during the first hour up to a maximum of 31.2 ± 3.9/h at 2 h after infusion. Compared to the pretreatment period the frequency remained significantly elevated during the 3rd (28.7 ± 2.3/h; P < 0.05) and 4th (20.2 ± 3.9/h; P < 0.05) hour after infusion. Seminal oestrogen therefore stimulate uterine contractions at Day 0 and may play a physiological role for sperm transport.