Changes in steroid hormones in plasma and myometrium and uterine activity in ewes during late pregnancy and parturition.

In 7 ewes during late pregnancy, peripheral plasma concentrations of oestrogens were correlated with uterine activity (P less than 0-01; r=+0-47). In myometrial tissue, the concentration of progesterone was similar to that in plasma; it rose to a plateau from Days 115 to 130 of pregnancy and then fell, but was still detectable during parturition. Myometrial oestrogen concentration was much higher than in plasma; from a peak at Days 100-115 it decreased, but rose sharply just before parturition.