Effects of prostaglandin E2 and oxytocin on the electrical activity of hormone-treated and pregnant rat myometria.

The effects of prostaglandin E2 (PGE2) and oxytocin on the electrical activity of rat myometrium at various stages of gestation and following hormonal treatment have been investigated. 1. PGE2 and oxytocin produce an excitation of the myometrial membrane under all experimental conditions. The sensitivity of the myometrium markedly increases during the last stage of gestation, and at parturition is more than one thousand times greater than in the mid-pregnant rat. The sensitivity of the myometrium to oxytocin increases rapidly during the last stage of gestation but to PGE2 the increase is gradual, beginning in the late middle stage of gestation. 2. During the early middle stage of gestation, the sensitivity of the myometrium to PGE2 and oxytocin is lower than in the non-pregnant myometrium. 3. After oestradiol treatment, the sensitivity to PGE2 and oxytocin increases but the sensitivity is much weaker than that during the parturition. On the other hand, after progesterone treatment, the sensitivity is reduced below that of the castrated rat. 4. Differences in the sensitivity of progesterone-treated and oestradiol-treated myometria to PGE2 and oxytocin are compared to those of the pregnant and post-partum myometrium. The results show that the sensitivity of the myometrium to PGE2 and oxytocin during the early and early-middle stages of gestation can be simulated by progesterone treatment, but that the sensitivity during the last stage of gestation and during parturition cannot be simulated by oestradiol and progesterone treatment.