Quantitative Changes in Myometrial Activity in the Guinea-Pig During Pregnancy

Dg, Porter

doi:10.1530/jrf.0.0270219

Cited by 19 publications

(7 citation statements)

References 18 publications

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“…Two patterns of uterine contractile activity occur during pregnancy in sheep and in other species, including humans (Csapo & Sauvage, 1968), monkeys (Germain et al, 1982), guinea-pigs (Porter, 1971), rats (Fuchs, 1969) and rabbits (Demianczuk et al, 1984). Throughout most of pregnancy in sheep, contractions (termed contractures by Nathanielsz and colleagues (1976)) are of low ampli¬ tude (0-27-0-67 kPa), long duration (3-8 min) and low frequency (2-3 h"1) (Hindson & Ward, 1973;Nathanielsz et al, 1976; Van der Weyden et al, 1981;Harding et al, 1982;Lye et al, 1983;Sigger et al, 1984;Garcia-Villar et al, 1984).…”

Section: Introductionmentioning

confidence: 99%

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

Sj¹

1992

Reproduction

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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: Introductionmentioning

confidence: 99%

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

Sj¹

1992

Reproduction

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“…The uterus of the guinea-pig is sensitive to oxytocin at all stages of gestation (Bell, 1941 ;Porter, 1971), whereas, in most other species, the uterus responds to oxytocin only towards term. It has been demonstrated that the posterior pituitary of the foetal guinea-pig is highly active at the time of parturition (Burton & Forsling, 1972).…”

Section: Introductionmentioning

confidence: 99%

Placental Transfer of Oxytocin in the Guinea-Pig and Its Release During Parturition

Am¹,

Illingworth²,

Challis³

et al. 1974

Journal of Endocrinology

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Oxytocin levels in pregnant and parturient guinea-pigs were studied by means of a sensitive and specific radioimmunoassay. Oxytocin was released from the maternal pituitary in substantial amount only during the expulsive phase of labour, when the mean concentration in carotid arterial blood in five animals was 503 pg/ml plasma (range 96\p=n-\2900 pg/ml). Oxytocin was not found in the plasma of the first born at the moment of birth, but was usually detected in amounts ranging from 96 to 455 pg/ml in those born subsequently. The mean half-time of oxytocin in the maternal circulation during late pregnancy was 62 \ m=+-\ 7\m=.\5 (s.e.m., n = 5) s. In-vivo experiments showed that the placenta was permeable to oxytocin in both directions.

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“…The mean and maximum amplitudes of the pressure complexes were greater early in gestation than in middle or late pregnancy (Text-figs la, d & g; Table 1). As shown by Porter (1971b), this is because the uterine lumen is small in relation to the thickness of the uterine wall.…”

Section: Resultsmentioning

confidence: 99%

“…In terms of maternal weight, there was a corresponding variation in the amount of noradrenaline administered. Due care must be taken when comparing intrauterine pressure tracings from different stages of pregnancy, since there is a complex relation between mechanical tension, wall thickness, and lumen diameter (Porter, 1971b). The amplitude of contractions was greater at 10-21 days p.c., when the fetus was still small, than at later stages, when the uterine wall had been distended by growth of the conceptus (Table 1).…”

Section: Discussionmentioning

confidence: 99%

Excitatory response of guinea-pig myometrium to intravenous noradrenaline declines towards term

Carter¹

1985

Reproduction

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Guinea-pigs were anaesthetized at three stages of pregnancy. Intrauterine pressure was recorded for a 1-h control period and during 10-min intravenous infusions of noradrenaline at rates of 1.0 and 10 micrograms/(min X kg). The mean and maximum amplitude of contractions occurring during the infusions was compared with that of contraction cycles registered in the control period. At 18-21 and 35-43 days post coitum, noradrenaline invariably evoked a rapid and sustained rise in intrauterine pressure, the amplitude of the contractions being greater than during spontaneous contraction cycles recorded in the control period. In late pregnancy, 59-68 days p.c., infusion of 1.0 micrograms noradrenaline/(min X kg) failed to elicit a clear response; contractions occurring during infusion of 10 micrograms noradrenaline/(min X kg) had amplitudes similar to those of the control period and were without a sustained contracture. The absence of denervation hypersensitivity, despite the occurrence of sympathetic denervation in the course of pregnancy, may be due to a generalized effect on excitation-contraction coupling, possibly caused by relaxin.

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Quantitative Changes in Myometrial Activity in the Guinea-Pig During Pregnancy

Cited by 19 publications

References 18 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

Placental Transfer of Oxytocin in the Guinea-Pig and Its Release During Parturition

Excitatory response of guinea-pig myometrium to intravenous noradrenaline declines towards term

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