Estrogen and progesterone receptors in the uterine artery of rats during and after pregnancy.

Changes in the level of estrogen and progesterone receptors in the uterine artery of the rat were studied during pregnancy in order to evaluate the estrogen dependency of this artery. The weight of the uterine artery and its content of estrogen and progesterone receptors were measured. The steroid receptor content was also measured in the uterus and aorta as the tissues of these organs are estrogen-responsive and non-responsive, respectively. The uterine artery weight increased more than fourfold up to the middle of pregnancy and towards the end of pregnancy increased even further. The increase in weight was parallel to the increase in the level of plasma 17 beta-estradiol. During pregnancy a dramatic increase was detected in the number of uterine artery estrogen receptors. The estrogen receptor level was highest at term pregnancy, and following birth decreased to a low value. The level of progesterone receptors in the uterine artery increased modestly, though significantly, during pregnancy, and rose steeply at puerperium. No meaningful changes were seen in the aorta. The changes in estrogen and progesterone receptor levels in the rat uterine artery wall during and after pregnancy may suggest estrogen dependency of this tissue.