Effects of Terbutaline on Human Uterine Motility at Term

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Abstract
The effects of the selective β2-receptor stimulator terbutaline on the activity of gravid, human myometrium were investigated in vitro and in vivo, before and after administration of different β-receptor blockers. Terbutaline, 0.2-1.0 μg/ml, inhibited the spontaneous contractile activity of isolated strips of myometrium. This effect was unaffected by the selective β1-receptor blockers practolol, 1 μg/ml, and H 93/26, 1 μg/ml. However, the non-selective blocker propranolol, 0.1 μg/ml, completely inhibited the terbutaline effects. The in vitro effects of terbutaline could be correlated with findings in vivo. Intra-uterine pressure was recorded in 4 pregnant women at term. Infusion of terbutaline, 10-15 μg/min, for 20-40 min, effectively inhibited both spontaneous and oxytocin-stimulated uterine activity. There was a moderate increase in maternal heart rate, but no consistent effect on maternal blood pressure. Fetal heart rate was little affected. The uterine effects of terbutaline were not influenced by practolol, 5-20 mg i.v., but completely inhibited by propranolol, 1-2 mg i.v. The results suggest that terbutaline inhibits uterine motility by effects on uterine β2-receptors and that it can be given in clinically effective doses without adverse circulatory effects on mother or fetus.

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