The effect of ovarian hormones on stress relaxation in the uterus of the pregnant rat.

Tissue strip taken from rat uterine ampulla on day 20 of pregnancy was elongated at a contrast rate in Tyrode's solution at 37 degrees C to the length of a specified peak stress, and the stress decline was recorded at this length. The stress decline in uterine strips of ovariectomized progesterone-treated rats was significantly slower than those in intact pregnant rats at any different peak stress and elongation rate examined. Treatment with estradiol as well restored the physical properties to the control levels. Changing the medium to Ca-free Tyrode's solution had no effect on stress relaxation. Results suggest that estrogen with progesterone improves stress relaxation in the rat uterus during late pregnancy by changing the state of the noncontractile elements in the tissue.