Estradiol modulation of ovine uterine activity

Windmoller, R.; Lye, Stephen J.; Challis, John

doi:10.1139/y83-112

Cited by 27 publications

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“…No significant difference was found between oxytocin stimulated activity before or during infusion of sodium meclofenamate. These data confirm our previous findings in nonpregnant sheep (Windmoller et al, 1983), that the action of oxytocin on the pregnant myometrium is not solely mediated by prostaglandins. Furthermore in those expiants with endometrial tissue attached there was also no difference in the response to oxytocin either in the presence or absence of sodium meclofenamate suggesting that in this model either the prostaglandin synthetic capacity of the endometrium is compromised or prostaglandin production by the endometrium does not play a major role in mediating the effects of oxytocin on the myometrium.…”

Section: Discussionsupporting

confidence: 92%

“…Similar findings have been reported by Mitchell & Flint (1978) in sheep in labour and by ourselves in nonpregnant oestrogen-treated sheep (Windmoller et al, 1983) using doses of MFA sufficient to block preterm labour. However, two studies (El Badry et al, 1984; Adrianakis & Walker, 1989) using 4-aminoantipyrine did report a complete abolition of contractions associated with a significant reduction in plasma prostaglandin levels.…”

Section: Discussionsupporting

confidence: 89%

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Evidence for an intrinsic control of myometrial contractile periodicity in sheep during pregnancy

Sj¹

1992

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Reduction in concentration of prostaglandins in plasma by administration of sodium meclofenamate to pregnant sheep failed to alter the frequency or duration of electromyographic activity bursts or the response to oxytocin of myometrial tissue transplanted to the omentum. However, a significant (P < 0.05) delay (8.6 +/- 3.8 versus 1.3 +/- 0.3 min) in the myometrial response to oxytocin was observed when the hormone was administered 1 min after a spontaneous burst of electromyographic activity compared with 15 min after a burst, indicating a period of refractoriness. Similarly, the myometrial threshold for electrical stimulation was higher at 10-25% of the interval between contractions than close to the expected time of the next contraction. Stimulation of the myometrium at intervals of 30 s revealed a cycling of the electrical stimulation threshold: significantly higher voltages were required to elicit responses between spontaneous bursts of electromyographic activity (18.0 +/- 2.2 V) than during bursts (11.3 +/- 1.6 V). In contrast, there was no voltage differential in animals close to labour (< 24 h). These data provide no evidence to support a role for prostaglandins in the generation of contractions during pregnancy, but suggest that periodicity of contractions is associated with inherent changes in myometrial responsiveness to stimulation, which could occur as a result of a cycling of the resting membrane potential.

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Section: Discussionsupporting

confidence: 92%

Section: Discussionsupporting

confidence: 89%

Evidence for an intrinsic control of myometrial contractile periodicity in sheep during pregnancy

Sj¹

1992

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“…Several previous studies have demonstrated that estradiol increases myometrial contractility in sheep (23,27); however, the molecular mechanisms associated with increased myometrial contractility are not clear. PGs are a powerful stimulant of myometrial contractility.…”

Section: Discussionmentioning

confidence: 91%

Prostaglandin Mediates Premature Delivery in Pregnant Sheep Induced by Estradiol at 121 Days of Gestational Age

et al. 2004

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The experiments reported here were designed for both in vivo and in vitro approaches in the same animals to obtain a better picture of the role of estrogen in the control of parturition. Chronically catheterized pregnant ewes were treated with vehicle (n = 5) or estradiol (n = 6), 5 mg twice a day, im for 2 d starting at d 119 of gestation. Maternal and fetal plasma estradiol, progesterone, and cortisol were measured by RIA and maternal plasma prostaglandin (PG) F2alpha was measured by enzyme immunoassay. Intrauterine PG H synthase 2 mRNA and protein and placental P450(c17)alpha hydroxylase mRNA were determined by Northern, in situ hybridization, Western blot analysis, and immunocytochemistry. Data were analyzed by ANOVA. Five of six estradiol-treated ewes delivered their fetuses within 48 h; however, the placenta was still retained 5-6 h after fetal delivery. Both maternal plasma estradiol and PGF2 alpha increased significantly in the estradiol-treated group. Maternal and fetal plasma progesterone and cortisol were not altered in either group. There were significant increases of PGH synthase 2 mRNA and protein in myometrium, endometrium, and maternal placenta but not in fetal placenta in estradiol-treated ewes. Placental P450(c17)alpha hydroxylase mRNA was not detectable in vehicle or estradiol-treated groups. Estradiol can, in the absence of increase in plasma cortisol, stimulate uterine PG production and induce labor, resulting in fetal delivery in the sheep. Failure of placental delivery after estradiol treatment suggests that estradiol alone is insufficient to stimulate some of the key changes required to complete delivery at the stage of gestation studied.

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“…Similar contractures during pregnancy have been observed in a number of species including man (Csapo & Sauvage, 1968), monkey 1984. Contractures have also been observed in pregnant sheep carrying dead fetuses (Harding et al, 1982) and in non-pregnant sheep (Ruckebusch & Bueno, 1976;Harding et al, 1982;Windmoller et al, 1983), indicating that the fetus plays little or no role in their production.…”

Section: Introductionmentioning

confidence: 99%

An in-vivo model to examine the electromyographic activity of isolated myometrial tissue from pregnant sheep

Lye¹,

Freitag²

1988

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Summary. Strips (2\m=.\5\ m=x\3\ m=. \ 5cm) of myometrium alone (MYO) or endometrium/ myometrium (ENDO/MYO) were removed from the pregnant horn of sheep (Day 110 of gestation) and transplanted to sites within the omental fat. These explants developed regular bursts of electromyographic (EMG) activity over a period of 7\p=n-\10 days, as well as a dose-dependent stimulatory response to oxytocin (50\p=n-\200 mU i.v.). The frequency (per 2 h) of EMG bursts in the MYO (5\m=.\3\ m=+-\ 0\m=.\2) and ENDO/MYO (5\m=.\2\ m=+-\ 0\ m=. \ 3) explants was significantly greater (P < 0\m=.\05) than that of the uterine myometrium (3\m=.\0 \ m=+-\ 0\m=.\1), while burst duration (min) in MYO (4\m=.\1\m=+-\ 0\ m=. \ 2) and ENDO/MYO (4\ m=. \ 1 \ m=+-\ 0\m=.\2)explants was significantly (P < 0\m=.\05) less than in the uterine myometrium (7\m=.\3\ m=+-\ 0\m=.\1). The EMG bursts were asynchronous between the explants and uterus, although systemic administration of oxytocin produced a synchronous burst of EMG activity in all three tissues. No differences in EMG activity or responsiveness were apparent between MYO and ENDO/MYO explants. Histological examination of the explant tissue revealed the presence of smooth muscle fibres regularly orientated into two layers; some loss of endometrial tissue was apparent in ENDO/MYO explants. To validate the mechanical integrity of this model we examined the in-vitro contractile activity of myometrial strips prepared from the explants. The strips developed regular spontaneous contractions and demonstrated a dose-dependent stimulation in response to the addition of oxytocin (10\m=-\10 to 10\m=-\4m) to the bath fluid. These results suggest that spontaneous contractures during pregnancy are probably not due to pulsatile release of stimulants into the systemic circulation, or the direct diffusion of stimulants from intrauterine tissues to the myometrium but are probably caused by factors within the myometrium itself.

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Estradiol modulation of ovine uterine activity

Cited by 27 publications

References 0 publications

Evidence for an intrinsic control of myometrial contractile periodicity in sheep during pregnancy

Evidence for an intrinsic control of myometrial contractile periodicity in sheep during pregnancy

Prostaglandin Mediates Premature Delivery in Pregnant Sheep Induced by Estradiol at 121 Days of Gestational Age

An in-vivo model to examine the electromyographic activity of isolated myometrial tissue from pregnant sheep

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