Effect of beta-adrenergic stimulation on oxygen metabolism in the fetal lamb

Catecholamines, which are released into the circulation during stress, incr ease fetal metabolism. This effect appears to be related to beta-adrenorece ptor stimulation. We examined the effect of isoproterenol infusion on umbil ical blood flow, oxygen delivery and consumption, and glucose and lactate u ptake in late-gestation fetal lambs. Isoproterenol increased umbilical bloo d flow, but oxygen delivery to the fetus did not increase. Umbilical venous oxygen content fell Linearly with the increase in umbilical blood how. It is proposed that oxygen delivery to the sheep fetus is at or near a maximum and that oxygen delivery cannot be raised by increasing umbilical blood fl ow because oxygen diffusion at the placental site is limited. Fetal oxygen consumption increased initially but returned to control levels with an incr ease in infusion rate. Blood glucose concentration increased during isoprot erenol infusion; this was due to release of glucose and not because of incr eased placental uptake. Fetal blood pH values fell in association with elev ated lactate levels. It is proposed that elevated glucose concentrations re sulted in increased metabolism of glucose, and because oxygen delivery coul d not be enhanced, increased anaerobic glycolysis caused lactate concentrat ion to rise.