Oxytocin Receptor Concentrations, Inositol Phosphate Turnover and Prostaglandin Release by Endometrium from Ewes Induced to Ovulate During the Early Postpartum Period

Jacqueline Wallace, M G THOMPSON, Raymond Aitken, M A CHEYNE

Research output: Contribution to journalArticle

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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 F2alpha (PGF2alpha) 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 muCi [H-3]inositol and treated with 0 or 2 mumol oxytocin/l for 30 min, then [H-3]inositol mono-, bis- and trisphosphates were quantified. Oxytocin stimulated total IPs in all day-5 and day-15 post-partum ewes, in three of four day- 10 ewes and in all day-15 control ewes. Basal endometrial PGF2alpha release measured in triplicate (100 mg/well) during a 2 h incubation was higher in post-partum versus control ewes on days 5 and 10 but not on day 15 of the cycle. Similarly, oxytocin stimulated PGF2alpha release to varying levels at all stages of the cycle in post-partum ewes but only on day 15 in control ewes. Irrespective of the treatment group endometrial oxytocin receptor number was significantly (P<0.001) correlated with oxytocin-stimulated IP turnover and PGF2alpha release.

Thus the induction of ovulation and the subsequent luteal phase in post-partum ewes is against a background of high oxytocin receptor expression and enhanced PGF2alpha release which in some ewes may contribute to abnormal luteal function.

Original languageEnglish
Pages (from-to)17
JournalJournal of Endocrinology
Volume136
Issue number1
Publication statusPublished - Jan 1993

Keywords

  • POSTPARTUM BEEF-COWS
  • NORMAL LUTEAL PHASES
  • ESTROUS-CYCLE
  • CORPORA-LUTEA
  • OVINE ENDOMETRIUM
  • AUTORADIOGRAPHICAL LOCALIZATION
  • PROGESTERONE SECRETION
  • BINDING
  • INVITRO
  • PREGNANCY

Cite this

Oxytocin Receptor Concentrations, Inositol Phosphate Turnover and Prostaglandin Release by Endometrium from Ewes Induced to Ovulate During the Early Postpartum Period. / Wallace, Jacqueline; THOMPSON, M G ; Aitken, Raymond; CHEYNE, M A .

In: Journal of Endocrinology, Vol. 136, No. 1, 01.1993, p. 17.

Research output: Contribution to journalArticle

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N2 - 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 F2alpha (PGF2alpha) 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 muCi [H-3]inositol and treated with 0 or 2 mumol oxytocin/l for 30 min, then [H-3]inositol mono-, bis- and trisphosphates were quantified. Oxytocin stimulated total IPs in all day-5 and day-15 post-partum ewes, in three of four day- 10 ewes and in all day-15 control ewes. Basal endometrial PGF2alpha release measured in triplicate (100 mg/well) during a 2 h incubation was higher in post-partum versus control ewes on days 5 and 10 but not on day 15 of the cycle. Similarly, oxytocin stimulated PGF2alpha release to varying levels at all stages of the cycle in post-partum ewes but only on day 15 in control ewes. Irrespective of the treatment group endometrial oxytocin receptor number was significantly (P<0.001) correlated with oxytocin-stimulated IP turnover and PGF2alpha release.Thus the induction of ovulation and the subsequent luteal phase in post-partum ewes is against a background of high oxytocin receptor expression and enhanced PGF2alpha release which in some ewes may contribute to abnormal luteal function.

AB - 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 F2alpha (PGF2alpha) 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 muCi [H-3]inositol and treated with 0 or 2 mumol oxytocin/l for 30 min, then [H-3]inositol mono-, bis- and trisphosphates were quantified. Oxytocin stimulated total IPs in all day-5 and day-15 post-partum ewes, in three of four day- 10 ewes and in all day-15 control ewes. Basal endometrial PGF2alpha release measured in triplicate (100 mg/well) during a 2 h incubation was higher in post-partum versus control ewes on days 5 and 10 but not on day 15 of the cycle. Similarly, oxytocin stimulated PGF2alpha release to varying levels at all stages of the cycle in post-partum ewes but only on day 15 in control ewes. Irrespective of the treatment group endometrial oxytocin receptor number was significantly (P<0.001) correlated with oxytocin-stimulated IP turnover and PGF2alpha release.Thus the induction of ovulation and the subsequent luteal phase in post-partum ewes is against a background of high oxytocin receptor expression and enhanced PGF2alpha release which in some ewes may contribute to abnormal luteal function.

KW - POSTPARTUM BEEF-COWS

KW - NORMAL LUTEAL PHASES

KW - ESTROUS-CYCLE

KW - CORPORA-LUTEA

KW - OVINE ENDOMETRIUM

KW - AUTORADIOGRAPHICAL LOCALIZATION

KW - PROGESTERONE SECRETION

KW - BINDING

KW - INVITRO

KW - PREGNANCY

M3 - Article

VL - 136

SP - 17

JO - Journal of Endocrinology

JF - Journal of Endocrinology

SN - 0022-0795

IS - 1

ER -