Pregnancy-associated inhibition of coronary artery atherosclerosis in monkeys. Evidence of a relationship with endogenous estrogen.

We investigated the influence of repeated pregnancy on diet-induced atherosclerosis in cynomolgus monkeys and sought to determine if circulating endogenous reproductive steroid levels were associated with the extent of coronary artery atherosclerosis. At necropsy, females which were pregnant one or more times were found to have coronary artery atherosclerosis which was one-fourth as extensive as that of intact females which had not been pregnant. Extent of coronary artery atherosclerosis correlated positively with mean total plasma cholesterol (Rho = 0.52, p less than 0.01) and inversely with high density lipoprotein (HDL) cholesterol (Rho = -0.48, p less than 0.01) concentrations; both decreased during pregnancy. Additionally, the extent of coronary artery atherosclerosis was found to have a strong inverse association (Rho = -0.66, p less than 0.001) with an index (area-under-the-curve) of magnitude and duration of the pregnancy-induced elevation in plasma 17-beta estradiol concentration. This association could not be explained by an interrelationship between estradiol area-under-the-curve and either plasma total or HDL cholesterol concentrations. There was no relationship between atherosclerosis extent and a similar index of plasma progesterone concentrations. These findings provide evidence for an inhibitory effect of endogenous estrogen on the progression of coronary artery atherosclerosis.