Changes in the adrenergic effects and membrane activity of the circular muscle of rat uterus during late pregnancy and postpartum.

Osa, Takuro; Ogasawara, T.

doi:10.2170/jjphysiol.34.113

Cited by 7 publications

(6 citation statements)

References 14 publications

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“…(1) The action potential in mid‐pregnant tissues was complex in form, consisting of simple spikes followed by a sustained depolarization to around ‐25 mV, while only simple spikes occurred at term. It has been suggested previously that the plateau potential in the circular myometrium of pregnant rats reflects a weaker K + and a stronger Ca 2+ conductance (Osa & Kawarabayashi, 1977), and in that tissue there is also a switch from complex action potential to simple spikes at term (Bengtsson et al 1984; Osa & Ogasawara, 1984). (2) A pronounced after‐hyperpolarization terminated the first spike action potential at term but was never recorded in tissues obtained at mid‐pregnancy.…”

Section: Discussionmentioning

confidence: 99%

Changes in the mechanisms involved in uterine contractions during pregnancy in guinea‐pigs

Coleman

Hart

Tonta

et al. 2000

The Journal of Physiology

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The mechanisms involved in contraction in guinea‐pig myometrium were compared at mid‐ and late pregnancy. Tension was recorded simultaneously with either membrane potential or cytoplasmic calcium ([Ca2+]i) in strips exposed briefly to prostaglandin F2α (PGF). PGF‐induced increases in tension were underpinned by action potentials followed by sustained depolarization and biphasic increases in [Ca2+]i at mid‐ (peak, 879 ± 199 nM; sustained, 298 ± 35 nM, n= 11) and late pregnancy (peak, 989 ± 302 nM; sustained 178 ± 33 nM, n= 8). At mid‐ and late pregnancy, nifedipine (10−6 M) reduced (a) the PGF‐induced increase in tension to 84 and 35 %, (b) the level attained during the depolarization by 2 and 12 mV and (c) the peak rise in [Ca2+]i to 42 and 17 %. The sustained rises in [Ca2+]i were resistant to nifedipine. In Ca2+‐free solution (containing 1 mM EGTA), PGF elicited an increase in tension that was 26 % of that in 2·5 mM Ca2+ and an increase in [Ca2+]i (24 % of the sustained level) at mid‐pregnancy but no increase in tension or [Ca2+]i at term. At both stages of pregnancy, PGF decreased the level of [Ca2+]i required to elicit increases in tension comparable to those evoked by high K+o. The slope of the tension‐[Ca2+]i curves were steeper in mid‐ than in late pregnancy. In conclusion, at mid‐pregnancy, the contractile response of the guinea‐pig myometrium to PGF involves Ca2+ influx through L‐type voltage‐operated Ca2+ channels (VOCCs) and by receptor‐operated mechanisms, release of Ca2+ from intracellular stores, and an increase in the sensitivity of the contractile apparatus to Ca2+. At term the situation is different: a modest increase in the sensitivity of the contractile apparatus to Ca2+ persists and there is a major reliance on Ca2+ influx through VOCCs.

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Section: Discussionmentioning

confidence: 99%

Changes in the mechanisms involved in uterine contractions during pregnancy in guinea‐pigs

Coleman

Hart

Tonta

et al. 2000

The Journal of Physiology

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“…In fact, the treatment of spayed rat with exogenous estradiol induces the generation of plateau potential in the circular muscle (OsA and OGA-SAWARA, 1979). A contradictory event is the generation of plateau potential in the circular muscle of rat uterus during midpregnancy (OsA and FUJINO, 1978;KISHIKAWA, 1981;KAWARABAYASHI and MARSHALL, 1981;OSA and OGASAWARA, 1984) when blood progesterone predominates. Thus, the plateau potential occurs in the circular myometrium by the dominance of either estrogen or progesterone.…”

Section: Discussionmentioning

confidence: 99%

Changes in action potential and .BETA.-adrenergic effects of the circular muscle of postpartum rat uterus.

1985

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Spike potential dominated in the circular muscle of postpartum rat uterus during the period between 0 and 15 hr after the delivery of the first newborn. During the postpartum period ranging between 20 and 48 hr, the plateau potential was dominant. Application of 10-9 M isoprenaline strongly depressed the contraction during early postpartum period (0-15 hr), and the depressant effect was much smaller thereafter. In vivo treatment of postparturient rats with estradiol-17j3 (50 µg) or progesterone (50 ag) for 2 days did not alter the postpartum change in action potential or the effect of isoprenaline. The postpartum changes in muscle properties mentioned above were prevented in the distended portion of uterus, when several fetuses and placentas were artificially kept inside the uterus for 2 days, while other fetuses were delivered out. The hormonal influences on the circular muscle of postpartum rat uterus were discussed in view of the above experimental findings.

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“…Contraction is potentiated when the frequency of spike discharge in a burst increases, and vice versa under the influence of external ionic environment and drug application (KURIYAMA, 1961;KURIYAMA and SUZUKI, 1976 b;. In the circular muscle during midpregnancy, contraction is potentiated when slow potential is prolonged, and vice versa (KAWARABAYASHI and OsA, 1976;KURIYAMA and SUZUKI,1976b;KISHIKAWA, 1981;OSA and OGASAWARA, 1984). By analogy, the potentiation of contraction caused by progesterone and the depression by estradiol in the longitudinal muscle on Day 21 and 22 of pregnancy are well correlated to the excitation and inhibition of electrical activity of the membrane, respectively.…”

Section: Discussionmentioning

confidence: 99%

Effects in vitro of progesterone and estradiol-17.BETA. on the contractile and electrical responses in rat myometrium.

Osa

Ogasawara

1984

Jpn.J.Physiol

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Uterine longitudinal and circular muscles from pre-and postterm rats were studied in vitro for their contractile and electrical activities under the influence of 20-100 ,uM progesterone, 20 ,uM estradioll7R, or 20 ,uM stilbestrol. Uterine longitudinal or circular muscle strips were irrigated by Krebs solution at 37°C containing one of the hormones mentioned above, dissolved by the use of ultrasonic wave. Muscle contractions were recorded by a force displacement transducer, and electrical activities of the muscle membrane were studied using an intracellular microelectrode. At diestrus and Day 14 of pregnancy, progesterone depressed the contractions of longitudinal muscle. At pre-term, progesterone potentiated the contractions and prolongated the membrane burst discharge of longitudinal muscles, while estradiol inhibited their contractions and suppressed spike activities. At the same stage of pregnancy, both progesterone and estradiol inhibited contractions of circular muscles. At post-partum, progesterone potentiated and then depressed longitudinal muscles, while estradiol inhibited their contractions. At this stage, both progesterone and estradiol inhibited contractions of circular muscles, although vigorous spike discharges were observed. Stilbestrol depressed contractions of both longitudinal muscles from diestrus rats and longitudinal ileal muscles from a guinea pig. In view of these findings, it was deduced that these ovarian hormones exert dual action on the uterine muscle in vitro, one through changes in the membrane activity and the other through dissociation of excitation-contraction coupling.

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Changes in the adrenergic effects and membrane activity of the circular muscle of rat uterus during late pregnancy and postpartum.

Cited by 7 publications

References 14 publications

Changes in the mechanisms involved in uterine contractions during pregnancy in guinea‐pigs

Changes in the mechanisms involved in uterine contractions during pregnancy in guinea‐pigs

Changes in action potential and .BETA.-adrenergic effects of the circular muscle of postpartum rat uterus.

Effects in vitro of progesterone and estradiol-17.BETA. on the contractile and electrical responses in rat myometrium.

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