Plasma from normal pregnant women alters the reactivity of rabbit aortic smooth muscle with functional endothelium.

1. The effects of normal human pregnant plasma on the reactivity of rabbit aortic rings with documented endothelium have been studied. The rings were incubated in plasma from either normal pregnant or non-pregnant women and the effects of incubation on their responses to noradrenaline (NA), calcium chloride stimulation and potassium chloride-induced relaxation were examined. 2. There was no significant difference in the responses to NA in rings incubated in plasma from either pregnant or non-pregnant women. 3. The responses of the rings, incubated in both types of plasma, to calcium chloride stimulation through receptor-operated channels were similar, but rings incubated in plasma from pregnant women demonstrated decreased sensitivity and contractility to calcium chloride stimulation through voltage operated channels. 4. Potassium chloride-induced relaxation was significantly enhanced in rings incubated in plasma from normal pregnant women. The pattern of the responses was unaltered by either de-endothelialization or pretreatment of the rings with indomethacin. 5. The effects of plasma from pregnant women are similar to what has been reported as characteristic of vascular smooth muscle in normal pregnancy.