Smooth Muscle Electrical Activity in the Oviduct, and the Effect of Oxytocin, Prostaglandin F2α, and Prostaglandin E2 on the Myometrium and the Oviduct of the Cycling Mare1

Abstract

Myoelectrical oviductal activity was evaluated during the estrus cycle in the mare using electromyography. The effects of 20 IU oxytocin (i.v.), 10 mg prostaglandin (PG) F2α (i.m.), and 10 mg PGE2 (i.m.) on electrical activity of the myometrium and myosalpinx were investigated. Electrodes were surgically implanted in the myosalpinx and in the myometrium of the uterine horn and body. Myoelectrical activity was analyzed for total activity, frequency and duration of activity bursts, intensity, and amplitude. Spontaneous myoelectrical activity of the oviduct was not affected by the stage of the estrous cycle. Significantly more activity was recorded from the myosalpinx than from the myometrium throughout the estrous cycle (57.3 ± 2.7% vs. 28.8 ± 1.6%). All treatments resulted in increased activity in the myometrium and myosalpinx. The duration of the effect was 1 h for oxytocin, 5 h for PGF2α, and 2 h for PGE2. Oxytocin and PGF2α treatment during estrus resulted in an increased number of uterine activity bursts of high intensity and amplitude, whereas these treatments during diestrus, compared to those during estrus, resulted in less frequent uterine activity bursts of longer duration. Characteristics of PGE2-induced myometrial activity were similar to those of oxytocin- and PGF2α-induced myometrial activity. Myoelectrical activity in the oviduct following treatments with oxytocin, PGF2α, and PGE2 was characterized by an increased duration of activity bursts, intensity, and amplitude. Oxytocin and PGF2α caused a decline in the number of oviductal activity bursts, while PGE2 treatment resulted in an increased number of activity bursts. Oxytocin treatment during diestrus resulted in longer duration of bursts compared to PGE2 treatment, and a higher intensity compared to PGF2α and PGE2 treatment. It was concluded that oxytocin, PGF2α, and PGE2 affect both the myometrium and the myosalpinx in the mare.