scholarly journals Development of Myometrial Electrical Activity during the First Half of Pregnancy in the Sheep

1984 ◽  
Vol 37 (3) ◽  
pp. 153 ◽  
Author(s):  
JN Sigger ◽  
R Harding ◽  
A Bailey
Keyword(s):  
Electrical Activity ◽  
Progressive Increase ◽  
Myoelectrical Activity ◽  
Plasma Progesterone ◽  
Uterine Activity ◽  
Uterine Contractions ◽  
Pregnant Sheep ◽  
Low Amplitude

Uterine myoelectrical activity was recorded in seven pregnant sheep covering the period between 13 and 75 days post-coitum. Activity in the myometrium was present at day 13 and took the form of intermittent spikes of low amplitude. Bursts of spikes of irregular duration became noticeable between days 25 and 40 but most were not coordinated throughout the myometrium. Coordinated bursts of myoelectrical activity, which could be recorded at several sites simultaneously, first appeared between 40 and 65 days. These bursts had similar characteristics to the myoelectrical activity associated with uterine contractions during the last third of gestation. The myoelectrical activity showed a progressive increase in amplitude during the first half of gestation. There was no relationship between plasma progesterone levels and the increase in amplitude or appearance of coordinated bursts of uterine activity.

Relationships of maternal–fetal plasma steroid and amniotic fluid electrolyte levels to uterine myoelectrical activity during late gestation in sheep

1984 ◽  
Vol 62 (12) ◽  
pp. 2377-2382 ◽  
Author(s):  
D. D. Kitts ◽  
C. R. Krishnamurti
Keyword(s):  
Amniotic Fluid ◽  
Electrical Activity ◽  
Direct Relationship ◽  
Temporal Changes ◽  
Late Gestation ◽  
Myoelectrical Activity ◽  
Bipolar Electrodes ◽  
Fetal Plasma ◽  
Uterine Contractions ◽  
Uterine Electrical Activity

Paired bipolar electrodes were implanted in the corpus and uterotubal junctions in pregnant ewes. The temporal changes in uterine myoelectrical activity were monitored in conjunction with maternal and fetal plasma steroid and amniotic fluid electrolytes to evaluate the mechanisms regulating the prepartal uterine contractions in the ewe. Increases in total uterine myoelectrical activity were significant (P < 0.001) at both uterine locations as term approached, although significant (P < 0.01) variation existed between individual animals. Significant correlations between maternal progesterone (P < 0.05) and maternal and fetal estrogens (P < 0.01) and uterine myoelectrical activity were observed. The decline in maternal progesterone to levels of 2.03 ± 0.4 ng/mL and concomitant increases in both maternal and fetal total estrogens (199.3 ± 4.7 and 262.5 ± 11.0 pg/mL, respectively) resulted in a relatively high maternal estrogen/progesterone ratio just prior to parturition and corresponded to an approximate fivefold increase in total uterine electrical activity. Fetal cortisol concentrations were not significantly correlated with uterine myoelectrical activity; however, a positive correlation (P < 0.05) between fetal cortisol and maternal estrogen/progesterone ratios was obtained. The results of this study demonstrate a direct relationship between changes in the maternal estrogen/progesterone ratios and frequency and patterns of uterine electrical signals just prior to parturition, which may be ultimately triggered by the surge in fetal corticosteroid production.

Relation between fetal arterial and oxytocin-induced uterine contractions in pregnant sheep

1984 ◽  
Vol 62 (10) ◽  
pp. 1337-1340 ◽  
Author(s):  
Stephen J. Lye ◽  
Mary E. Wlodek ◽  
John R. G. Challis
Keyword(s):  
Positive Relationship ◽  
Late Pregnancy ◽  
Oxygen Electrode ◽  
Experimental Paradigm ◽  
Uterine Activity ◽  
Significant Positive Relationship ◽  
Uterine Contractions ◽  
Intrauterine Pressure ◽  
Pregnant Sheep ◽  
Maximum Decrease

The relation between oxytocin-induced type A uterine contractions and fetal arterial [Formula: see text], measured continuously with an intravascular oxygen electrode, was studied in nine chronically catheterized sheep during late pregnancy. Oxytocin provoked dose-related increases in intrauterine pressure (IUP) and decreases in fetal [Formula: see text]. There was a significant positive relationship between changes in IUP and the maximum decrease in fetal [Formula: see text] (average r = 0.696, df = 92; P < 0.001). We conclude that changes in uterine activity contribute to transient fetal hypoxemia, and that administration of exogenous oxytocin provides an experimental paradigm to examine the consequences of this relationship.

Tissue-specific concentration changes of estrone and estradiol during spontaneous and ACTH-induced parturition in sheep

1987 ◽  
Vol 65 (2) ◽  
pp. 130-135 ◽  
Author(s):  
S. G. A. Power ◽  
J. R. G. Challis
Keyword(s):  
Normal Pregnancy ◽  
Progressive Increase ◽  
The Other ◽  
Fetal Membranes ◽  
Tissue Specific ◽  
Uterine Contractions ◽  
Sequence Of Events ◽  
Estrogen Production ◽  
Concentration Changes ◽  
The Mean

Changes in estrogen production are considered important in the sequence of events leading to parturition. We sought tissue-specific changes in the concentration of unconjugated estrone (E1) and estradiol (E2) in intrauterine fetal (amnion, chorion) and maternal (endometrium, myometrium) tissues during normal pregnancy, labour, and ACTH-induced labour in sheep. The mean concentrations of E1 and E2 in the fetal membranes were higher than in endometrium and myometrium. In amnion there were no consistent changes in estrone concentrations with gestation, although estradiol concentrations increased between day 130 and term. In the endometrium there were increases in both estrone and estradiol between day 100 and term, whereas in the myometrium increases in the concentrations of E1 and E2 occurred between days 130–135 and term. Animals showing a labourlike pattern of uterine contractions after intrafetal ACTH administration did not show significant differences in estrone or estradiol concentrations in amnion, chorion, or endometrium compared with saline-infused controls. However, there was a progressive increase in the concentration of estrone and estradiol in the myometrium during ACTH-induced labour. We conclude that changes in the concentrations of estrone and estradiol in intrauterine tissues vary between the tissues studied and the two estrogens. In general, estrogen concentrations increased towards term, but this trend was more marked in the maternal than fetal tissues. The changes in estrone concentrations in myometrium, but not in the other tissues, were replicated during ACTH-induced labour. Our results would be compatible with the suggestion that tissue-specific changes in estrogen concentrations may contribute to the local intrauterine steroid milieu during pregnancy and at term.

Failure of magnesium sulfate infusion to inhibit uterine activity in pregnant sheep

1997 ◽  
Vol 177 (1) ◽  
pp. 185-189 ◽  
Author(s):  
Hani A. Akoury ◽  
Susan E. White ◽  
Jacobus H. Homan ◽  
Vincent Y.T. Cheung ◽  
Bryan S. Richardson ◽  
...  
Keyword(s):  
Magnesium Sulfate ◽  
Uterine Activity ◽  
Pregnant Sheep

SUPPRESSION OF UTERINE ACTIVITY DURING MENSTRUATION BY EXPANSION OF THE PLASMA VOLUME

1971 ◽  
Vol 66 (1) ◽  
pp. 183-192 ◽  
Author(s):  
Anna-Riitta Fuchs ◽  
Elsimar M. Coutinho
Keyword(s):  
Isotonic Saline ◽  
Control Group ◽  
Plasma Expansion ◽  
Uterine Activity ◽  
Vascular Volume ◽  
Uterine Contractions ◽  
Vasopressin Secretion ◽  
Menstruating Women ◽  
Experimental Group ◽  
Marked Suppression

ABSTRACT Vascular volume was expanded in 10 normal, non-hydrated women with an infusion of 1000 ml of an iso-oncotic solution over 1.5 to 2 h and the effect of such treatment on uterine activity was studied on day 2-4 of the menstrual cycle. Three different plasma expanders were used and the results were similar with them all. The uterine recordings taken by means of a small intra-uterine balloon showed no immediate effect of the infusions, but about two hours later a marked suppression in uterine activity was noted in all and in seven instances the contractions disappeared almost completely and remained absent for two to three hours at least. Vasopressin elicited strong uterine contractions when the activity had been suppressed by plasma expansion. In a control group of 10 menstruating women who received no infusion, a decrease in uterine activity was never observed; on the contrary, the activity increased in 8 of the 10 subjects. In a group of ten receiving isotonic saline, uterine activity either remained unchanged or was somewhat reduced but much less than after infusion of iso-oncotic solutions. During the day a gradual decrease in the hourly diuresis occurred in the control group, whereas in the experimental group the urine output started to increase one to two hours following the infusion. The women receiving a saline infusion showed a slight transient increase in diuresis. It is suggested that the suppression of uterine activity following infusion of iso-oncotic solutions is due to reduction in vasopressin secretion brought about by the increase in vascular volume, and that endogenous vasopressin is a physiological stimulus for the uterine contractions during menstruation.

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