Effect of parasympathetic and beta-adrenergic blockade on the umbilical circulation in the unanesthetized fetal sheep.

Parasympathetic and beta-adrenergic blocking agents were administered to near term chronically instrumented sheep. Parasympathetic blockade resulted in a significant increase in fetal heart rate and fetal arterial blood pressure, with a minimal nonsignificant increase in umbilical blood flow. beta-Adrenergic blockade resulted in a decrease in fetal heart rate and umbilical blood flow, though neither was statistically significant. There was no change in arterial blood pressure. The net result of parasympathetic and beta-adrenergic blockade on fetal heart rate suggests that the intrinsic rate is the same as when these influences are present.