Increase of uterine motility and simultaneous decrease of progesterone concentrations in the rat after bilateral ovariectomy at mid-pregnancy

Abstract

Comparison of uterine activities recorded during the control period to those obtained during the two recording periods after ovariectomy (0-30 min and 30-60 min) showed an increase of the amplitude of uterine contractions (P less than 0.005) and a decrease of the interval between two successive uterine contractions (P less than 0.005) and the delay of electrical activities (P less than 0.005). Progesterone treatment (50 mg/kg i.m.) of ovariectomized rats prevented the abrupt fall in plasma progesterone concentrations, measured by RIA, which in turn inhibited the increase of uterine mechanical and electrical activities. A close relation between the increase of myometrial activity and the decrease of progesterone concentrations after ovariectomy is suggested. The activation of the myometrium would be principally induced by the fall of progesterone or by the variation of the oestrogen/progesterone ratio; these changes in sexual steroid hormones would augment the uterine sensitivity to physiological stimuli or modify the activity of other factors involved in the regulation of the myometrium.

Identification of Loci and Pathways Associated with Heifer Conception Rate in U.S. Holsteins

“…Potassium channels play an important role in fertility due to their actions on uterine function, adaptation to pregnancy and contractility [ 60 , 61 , 62 ]. Early pregnancy is characterized by the suppression of uterine motility and high concentrations of progesterone, whereas late pregnancy is dependent on increased motility and estrogen during the last 14 days of pregnancy [ 63 ]. Estradiol has a stimulatory effect on potassium channels causing increased excitability, whereas progesterone has an inhibitory effect [ 55 ].…”

Effect of partial starvation onin vitrospontaneous activity and glycogen levels of uterine smooth muscle from pregnant and non pregnant rats

“…This difference in contractile behaviour may be attributed to the level of progesterone, that would determine the scarce uterine activity seen at mid-term pregnancy (KURIYAMA & SUZUKI, 1976), while its rapid descent at term converts the uterus into a reactive organ (FUCH, 1978;CLABAUT et al, 1988).…”

Fetal viability and fetal growth after prolonged uterine contractions induced by progesterone withdrawal in late pregnancy in rats

“…In late pregnancy in rats, progesterone withdrawal, by ovariectomy or by administration of antiprogestational steroid, also causes an increase in uterine contractility (Clabault et al, 1988; Arkaravichien & Kendle, 1992). In our previous study (Arkaravichien & Kendle, 1990), it was shown that progesterone replacement in rats ovariectomized on day 15 of pregnancy could be delayed up to 36 h after ovariectomy, when uteri might have been contracting for quite a long period, without significant reduction in fetal viability.…”