Myoendothelial and placental blood flow responses to ritodrine infusion in the guinea pig.

The effect of ritodrine hydrochloride on uterine blood flow was investigated in near-term guinea pigs. The infusion of ritodrine in doses sufficient to inhibit uterine activity provoked tachycardia, and the cardiac output tended to rise. The percentage of cardiac output reaching the gravid uterus did not alter during the infusion of 12 micrograms per minute of ritodrine but decreased from 12% to 10% when the infusion rate was 120 micrograms per minute. There was an increase in the myoendothelial fraction of cardiac output in both instances, whereas the placental fraction decreased at the higher rate of infusion. Perfusion of the myoendothelial tissue improved during the infusion of 12 or 120 micrograms per minute of ritodrine, increasing by 25% and 18% respectively. No significant alteration occurred in the perfusion of the placental tissue.