Maternal and fetal metabolic responses to ritodrine in the sheep

Ritodrine hydrochloride was infused intravenously for 60 minutes into pregnant ewes or for 29 minutes into fetal lambs, during the last third of gestation. The maternal and fetal acid-base balance and carbohydrate status was determined prior to, during, and after the ritodrine infusions. Ritodrine was also infused into pregnant sheep in labor until no further inhibition of uterine activity could be achieved. In these studies, acid-base balance was frequently assessed. The maternal or fetal infusion of ritodrine resulted in no major changes in maternal or fetal acid-base balance during the periods of study. Lactate and pyruvate concentrations in mother and fetus rose during the infusion. The lactate/pyruvate ratio remained stable, suggesting an increase in both aerobic and anaerobic glycolysis. Maternal glucose concentrations were significantly elevated after one hour of the ritodrine infusions to the ewes, but minimally elevated in the fetus. Fructose concentrations were unchanged. The possible role as fetal fuels of increased metabolic products of glycolysis caused by beta-adrenergic stimulation is discussed.