Oxytocin receptor concentrations, inositol phosphate turnover and prostaglandin release by endometrium from ewes induced to ovulate during the early post-partum period

Abstract

Induction of ovulation early post partum in sheep is associated with a high incidence (30-40%) of premature luteolysis. The present study was designed to characterize oxytocin receptor levels, oxytocin-stimulated inositol phosphate (IP) turnover (second messenger) and oxytocin-stimulated prostaglandin F2 alpha (PGF2 alpha) release in the endometrium of post-partum ewes induced to ovulate 21 days after parturition and expected to exhibit a range of corpus luteal functions subsequently. Ovulation was induced on day 21 post partum using a controlled internal drug release device and pregnant mare serum gonadotrophin, and uterine tissues were collected on days 5, 10 or 15 of the cycle (n = 4/day). A further 12 ewes whose interval from previous parturition exceeded 150 days were similarly treated and acted as controls. Measurement of daily peripheral progesterone concentrations revealed that while all control ewes exhibited normal luteal function, abnormal luteal function was evident in two, two and one post-partum ewes studied on days 5, 10 and 15 of the cycle respectively. Oxytocin receptor binding was detected (by receptor-binding assay and in-vitro autoradiography) in the endometrium and myometrium of post-partum ewes at all three stages of the oestrous cycle but only at day 15 in control ewes. To determine IP turnover, 100 mg caruncular endometrium was incubated in duplicate for 2.5 h with 10 microCi [3H]inositol and treated with 0 or 2 mumol oxytocin/l for 30 min, then [3H]inositol mono-, bis- and trisphosphates were quantified.(ABSTRACT TRUNCATED AT 250 WORDS)

Resumption of oestrous and ovarian cyclicity during the post-partum period in autumn-lambing ewes is not influenced by age or dietary protein content

“…Sharpe et al (1986) reported that corpora lutea obtained from post-partum ewes are lighter and have lower LH receptor populations than those obtained from cyclic ewes, while Wallace (1995) demonstrated a lower steroidogenic capacity in vitro. Restoration of functional integrity appears to take longer however as Fredriksson (1985) reported elevated circulating concentrations of 15keto-13,14-dihydro-PGF2oc, a metabolite of PGF2°=, for up to 28 days post partum and Wallace et al (1993) detected high concentrations of uterine oxytocin receptors, an integral part of the luteolytic mechanism, as late as day 35. Rubianes and Ungerfeld (1993) observed that, in autumn lambing Corriedale ewes, macroscopic uterine involution was completed by day 17 post partum.…”