Changes In Intrauterine Pressure Research Articles

The relationship between progesterone, uterine volume, intrauterine pressure, and clinical progress in hypertonic saline—induced abortions

During hypertonic saline—induced abortions, intrauterine pressure (IUP) and plasma progesterone (P) have been measured and the uterine volume (V) estimated in 13 patients. During the initial third of the instillation-abortion time, the decrease in P was proportionately greater than the increase in IUP, indicating that P withdrawal precedes the evolution of IUP and clinical progress. In 2 additional patients, with low P levels, the evolution of IUP and abortion have been induced by a mere increase in V, using isotonic (rather than hypertonic) saline. In these 2 patients P withdrawal only manifested when the evolution of IUP approached completion. Since the changes in P did not account fully for the changes in IUP, the ratio V/P was calculated at various phases of hypertonic saline—induced abortion. It then became apparent that whenever V increases or P decreases markedly, without compensatory changes in P or V, the IUP evolves and pregnancy terminates. It is concluded that current concepts in myometrial regulation may be advanced by quantitating V and P in individual patients whose IUP is measured.

Uterine activity in late pregnancy and during parturition in the rat.

Uterine activity was recorded in 17 unanesthetized, unrestrained pregnant rats by means of intrauterine balloons inserted at a previous operation. Recordings of intrauterine pressure changes were obtained from Day 18 of gestation onwards and throughout spontaneous delivery, which occurred on Days 22 or 23 of gestation. Oxytocin was injected intravenously through an indwelling polyethylene catheter at intervals. The uterus of the pregnant rat was never quiescent except for short periods of time and it responded to moderate doses of oxytocin (10 mU) throughout the period studied. However, a changing pattern and character of contractions was consistently observed in late pregnancy and toward term the intensity of the uterine response to oxytocin increased markedly. Parturition occurred at a time when the uterine oxytocin sensitivity was maximal. The expulsion of the litter was preceded by a period of continuous uterine activity lasting 2.5 hr on the average and by a period of 5-30 mm of bearing down efforts before the delivery of the first fetus. The deliver�� of successive littermates was associated with continuous uterine activity and only a few abdominal straining efforts, and lasted 1.5 hr on the average. After the last fetus and placenta were born the uterine activity disappeared quickly and in 10-30 mm the uterus was completely quiescent except for infrequently occurring cycles consisting of 3-4 contractions. Rhythmic regular activity started 8-12 hr postpartum.

Parturition in the rabbit.

Intra-uterine pressure changes have been successfully recorded in ewes in late pregnancy and during parturition using endoradiosondes (Hindson, Schofield, Turner & Wolff, 1965; Hindson, Schofield & Turner, 1968). This device is superior to intra-uterine balloons, for the sonde is not fixed in the uterine cavity and has no connexion with the exterior. Furthermore, in rabbits, recordings may be made with the aerial around the cage, not the animal, as is necessary to pick up adequate signals in the sheep. Thus the animal is unrestrained and undisturbed, being free to move in the cage while continuous recordings are made over several days. It was thought appropriate, therefore, to extend radio-telemetry recordings to the rabbit and supplement information already obtained with intra-uterine balloons (Fuchs, 1964; Porter & Schofield, 1966). Large New Zealand White rabbits were used in order to diminish the sonde/foetus size ratio. On the 23rd day of pregnancy the

Parturient pressures in the ovine uterus.

1. Intra-uterine pressure changes were followed by radio-telemetry in ten ewes carrying one lamb in each horn. One endo-radiosonde was implanted in each horn some 2-3 weeks before term and the pressure changes in the two horns were recorded simultaneously thereafter.2. The first isolated pressure waves which could be ascribed to myometrial activity were detected about 12 hr before delivery. Once pressure waves had become established, it was found that one horn developed waves which were about double the amplitude of those in the other horn and of greater duration. Thus one horn became dominant and the lamb occupying this horn was the first to be presented at the cervix. There appeared to be no difference between the two horns in the frequency of the waves.3. Digital examination of the os led to a phase of increased pressure waves which was considered to be due to oxytocin release.4. These findings are discussed and it is suggested that some local factor maintains the dominance of one horn and that this factor may be related to the local influence of the placenta.

Spontaneous and pharmacologically induced disruption of myometrial activity in the early puerperium

Intrauterine and myometrial pressure changes were measured in the intact puerperal human uterus (14 subjects). Major differences between the spontaneous myometrial activity of various regions were observed. Intramyometrial injection of procaine caused localized disruption of the recorded activity. This action of procaine was obliterated by concomitant oxytocin infusion.

The Effect of a Single Dose of Stilboestrol on Cervical Dilation in Pregnant Sheep

Radio telemetric recordings of intra-uterine pressure changes were carried out in ewes during the last 2 to 3 weeks of pregnancy. Observations were made on 6 normal ewes to add to the data from a control series reported previously. A single dose of 20 mg. stilboestrol was injected into 14 ewes, either in mid-pregnancy or within 2 weeks of term. Of these, 4 ewes developed a riug-womb-like condition and the cervix had to be dilated manually; 2 developed a genuine ring-womb and had to be sectioned. All had had labours of at least twice the control span and the intra-utcrine pressure waves recorded were indistinguishable from those in the control series. Sondes inserted through the cervix in 2 experimental ewes and in 13 clinical ring-womb cases after therupture of the amniotic sac are not considered to give a true refection of pressures impinging on the cervix to bring about dilation. It is concluded, tentatively, that ring-womb is primarily a disorder of the cervix and that the naturally occurring condition may be hormonal in origin.

Intra-uterine pressure changes during pregnancy and parturition in rabbits.

SUMMARY Small balloons attached to polyethylene tubing were inserted into either end of one uterine horn in rabbits on about the 22nd day of pregnancy. The tubing was threaded subcutaneously and brought out through an incision at the back of the neck; recordings of intra-uterine pressure changes were made up to and including parturition. There were no pressure changes which could be ascribed to contraction of the myometrium until an average of 31 hr. before delivery of the first foetus but there was considerable variation. Pressure waves recorded from the two balloons were often different in frequency and amplitude and were seldom synchronous. In none of the rabbits did one end of the horn develop 'parturient pressure' before the other and, in general, pressure at the ovarian end of the uterus was higher than at the cervical end. The rabbits could be divided into two groups: (I) those in which the onset of delivery was abrupt and preceding pressure waves were of low amplitude; (II) those in which the pressure waves increased gradually in intensity over several hours before delivery. Both the duration of delivery and the mortality rate of the foetuses were significantly greater in group II than in group I. The results in group I are consistent with the concept that in the normal rabbit parturition is initiated by a release of oxytocin. It is suggested that in group II oxytocin release failed to occur and that this failure was due to 'emotional stress' and possibly circulating adrenaline.