Reversal of the effects of 4-amino-antipyrine on myometrial and cervical electromyographic activity by PGF2 alpha in the ovariectomized estradiol-replaced non-pregnant ewe.

Cervical and uterine electromyograms (EMG) have been recorded from ovariectomized non-pregnant ewes. When the animals were infused with saline, the frequency of EMG events lasting less than 180 seconds was not different from those lasting more than 180 seconds. During infusion of estradiol at 100 micrograms X 24 hours-1 into the maternal jugular, the frequency of events less than 180 seconds increased significantly in the myometrium and in the cervix. Contracture activity (events lasting more than 180 seconds) was not significantly different in the myometrium compared to the cervix before estradiol administration. During estradiol infusion, the contracture activity remained unchanged. During 4-amino-antipyrine (4AA) administration, the contracture activity decreased significantly in the myometrium, while an insignificant change occurred in the cervix. This state was associated with a decrease in the venous PGFM:6-keto F1 alpha plasma ratio. Infusion of PGF2 alpha (.5 micrograms min-1 and 1.0 microgram X min-1 for ten minutes) into the femoral artery resulted in a significant increase in the frequency of events less than 180 seconds in both the myometrium and cervix. For the duration of the ten-minute infusion, the activity was contracture-like. These findings suggest that the cervix may not only be influenced by mechanical properties (stretch) and local paracrine factors but also by various stimulators and inhibitors irrespective of the myometrium.