THE IN VIVO EFFECTS OF BETA ADRENERGIC STIMULATION AND BLOCKADE ON THE HUMAN UTERUS AT TERM

¹ Departments of Pharmacology, Obstetrics and Gynaecology, University of Alberta, Edmonton, Alberta, Canada

Three patients were studied close to term. Intrauterine and intraarterial pressures were monitored by catheters and pressure transducers. Intravenous infusions of isoproterenol (IS) were shown to inhibit uterine contractions, whether these contractions were induced by Syntocinon or were a result of natural labor. The dosage of IS required to produce greater than 50% inhibition varied from 2 to 8 µg/min and was accompanied by a fall in blood pressure and an increase in heart rate. All these effects were blocked by propranolol given as single i.v. injections from 1 to 4 mg. No untoward effects, which would have been evidenced by marked changes in heart rate, were observed on the fetus. It is concluded from these studies that beta-receptor stimulation produces inhibition of the human uterus at term, and beta-receptor blockade reverses this inhibition.