Myometrial and cardiovascular responses to alterations in plasma epinephrine and norepinephrine

Plasma epinephrine and norepinephrine levels were determined when these hormones were separately infused into patients in labor. Norepinephrine caused increased incoordinate uterine activity and a pressor response. Epinephrine diminished uterine activity during spontaneous and oxytocin-induced labor. Increased tonus was noted in half the cases of spontaneous labor once the infusion was discontinued. The major cardiovascular response to epinephrine was depressor. When the infusion was discontinued, a rapid decrease in plasma hormone levels was seen and normal values were attained within 5 minutes. These plasma levels were correlated directly with uterine activity but not with the cardiovascular response which persisted for a longer period of time.