Resistance of the rat embryo to elevated maternal epinephrine concentrations.

This study examined the effects of a chronic maternal infusion of epinephrine on development of the rat embryo. Epinephrine was infused during days 1 to 8, 8 to 15, or 15 to 22 of pregnancy to cover periods of implantation, embryogenesis, and rapid fetal growth, respectively. Infusions were accomplished with osmotic minipumps to avoid repeated handling stress. The infusion rate of 0.125 micrograms/min elevated resting plasma concentrations of epinephrine in nonpregnant rats by about sevenfold (from 0.28 to 1.98 ng/ml). Under these conditions, epinephrine did not affect the number of rats maintaining pregnancy, their litter size, or the numbers of resorptions, fetal deaths, and malformations. Fetal and placental weights were unaffected except for a slight trend for fetal weight to be depressed in larger litters of rats treated during days 15 to 22. It seems that the rat embryo is resistant to elevations of epinephrine concentrations equivalent to those observed under mild to severe stress conditions.