Effect of continuous infusion of fenoterol on maternal pelvic and fetal umbilical blood flow in pregnant sheep.

The results from studies on the reactions of the uterine vascular bed upon intravenous administrations of beta-adrenergic drugs to the ewe are not all identical. This can be partly explained by different reactions of the pelvic vasculature on beta-adrenergic receptor stimulation. In order to assess whether any differences in flow reactions existed between the vascular beds of two maternal pelvic vessels upon beta-adrenergic receptor stimulation, we studied the effect of continuous maternal intravenous infusion with fenoterol on the blood flow in the maternal internal iliac and the median uterine artery in seven chronically instrumented pregnant sheep between 104 and 142 days gestation. Furthermore, the effects on umbilical venous blood flow, fetal heart rate, blood pressure and acid-base balance were analyzed. Maternal and fetal blood flows were measured with electromagnetic flow transducers. Fenoterol was administered to the ewe via a continuous intravenous infusion in two sequential periods of 30 minutes duration in a dose of 2 respectively 4 micrograms per minute. The blood flow in the internal iliac artery showed an increase of 10.5% (p less than 0.05) at the end of the infusion period and was still but not significantly elevated during the postinfusion period. No significant changes in median uterine artery blood flow were found during the fenoterol infusion, although an incremental trend was present. Fenoterol infusion to the mother had no effect on umbilical venous blood flow. Fetal pH and PO2 did not change, while fetal PCO2 was reduced (p less than 0.005) at the end of the infusion and recovery period, probably as a result of the concomitant maternal hyperventilation.(ABSTRACT TRUNCATED AT 250 WORDS)