The effects of ovariectomy and stretch on the regulatory profile and activity of the uterus

Abstract

Following ovariectomy of five New Zealand white rabbits at day 25 of pregnancy, the intrauterine pressure (IUP) and uterine progesterone (P) and prostaglandin (PG) levels were measured sequentially at days 25, 26 and 27. At day 25, when the uterine P and PGE and PGF were high, massive intrauterine treatment with 500 microng PGF2alpha provoked only a sustained contracture on which only low level oscillation in IUP was superimposed. At day 26, when the P levels had decreased significantly (P less than 0.001) and the PG levels had not changed significantly, 50 microng PGF2alpha significantly increased cyclic IUP as compared with the day 25 value (P less than 0.001). At day 27, when the P levels decreased further, as little as 5 microng PGF2alpha provoked still higher cyclic IUP, in spite of a significant reduction in PG levels (P less than o.05). Stretching the uterus of six post partum and six 26 days pregnant rabbits (after removing the uterine contents) significantly increased the uterine PGF levels (P less than o.001). However, stretch increased only cyclic IUP of the post partum uterus and was without effect on the pregnant uterus, which still had high P levels. These results indicate that the myometrium is activated by exogenous PG or stretch, regardless of whether the uterine PG levels increase, remain unchanged or even moderately decrease, provided that the uterine P levels are reduced to a critical value.