[Uterine motor responses to catecholamines in the ewe under different steroidal impregnations. Demonstration of the role of endogenous catecholamines].

The electromyographic activity (EMG) of the uterus was recorded in vivo in 6 conscious ovariectomized ewes treated with oestrogen. In 6 cyclic ewes, changes in intrauterine pressure were recorded at the same time as the EMG. Motor responses to noradrenaline, isoprenaline and adrenaline injections were studied at 3 uterine sites in the ovariectomized ewes. Uterine activity was stimulated by noradrenaline and inhibited by isoprenaline, providing evidence that there were both alpha and beta-adrenergic receptors in the myometrium of the oestrogen-treated ovariectomized ewes. Adrenaline caused an increase of myometrial activity at the cervical end and the middle of the uterine horn, demonstrating that alpha-receptors were predominant. Adrenaline had little effect on activity at the tubal end of the horn, but after the administration of propranolol, a blocker of beta-adrenergic receptors, there was a stimulatory effect. These results show that the alpha-receptor/beta-receptors, there was a stimulatory effect. These results show that the alpha-receptor/beta-receptor ratio along the uterine horn was not constant. In cyclic ewes, the effects of noradrenaline and adrenaline in the middle of the uterine horn were stimulatory during oestrus and luteal phase, indicating that alpha-receptors were predominant in that region under both oestrogenic and progesteronic dominance. The perfusion of phentolamine, a blocker of alpha-adrenergic receptors, into ovariectomized ewes treated with oestrogen provided evidence that endogenous catecholamines modulate uterine activity.