ÉTUDE ÉLECTROMYOGRAPHIQUE DE LA MOTRICITÉ DE L'UTÉRUS CHEZ LA BREBIS. ACTION DES HORMONES

Abstract

Electrical and mechanical activity of the myometrium was recorded in 46 ewes, including both cyclic animals and ovariectomized animals treated with estrogen or progesterone. In ovariectomized ewes, estrogen induces rhythmic electromyographic activity composed of bursts of action potentials related to variations in intra uterine pressure. Maximum EMG activity occurs 24-36 hours after treatment with estradiol benzoate, the beginning of estrus. After estrogen treatment, low doses of oxytocin provoke a continuous discharge of action potentials, while high doses abolish them. After progesterone treatment, uterine EMG activity is composed of slower variations in potential unrelated to myometrial contractions. In cyclic ewes during estrus the uterus exhibits spontaneous rhythmic EMG activity, identical with that induced by estrogen in the ovariectomized animal. This activity, characterized by bursts of action potentials, is confined to the last day of the cycle and the first 3 days of the following cycle, except in a few ewes which showed spontaneous activity on the 6th day. In the conscious ewe, ovariectomized and estrogen-treated or intact at the beginning of estrus, vaginal stimulation induces a marked increase in myometrial electrical activity; no such effect is produced in the anesthetized animal.