Estradiol modulation of ovine uterine activity

The effects of continuous estradiol-17 beta (E2) infusion (100 micrograms/24 h and 1 mg/24 h) on spontaneous myometrial activity and uterine responsiveness to oxytocin (OT) and prostaglandin (PG) F2 alpha were measured in nonpregnant sheep. Continuous recordings were made of intrauterine pressure (IUP) and uterine electromyographic (EMG) activity. Continuous E2 infusion resulted in an accentuated pattern of uterine quiescence alternating with periods of high activity lasting 6-8 h. Short (3-10 min) periods of elevated resting IUP and intense EMG activity increased in frequency after E2. E2 also increased the rate of rise of IUP cycles. Within 30 h of commencement of E2 infusion the uterine response to a bolus challenge of OT or PGF2 alpha increased significantly; dose-related responses to OT and PGF2 alpha were measured after 4 days E2 infusion. The response to OT was not abolished by infusing meclofenamic acid. We conclude that: (i) continuous E2 infusion results in a pattern of uterine activity characterized by alternating high activity and quiescence, and increased frequency of occasional rises in basal IUP; (ii) E2 induced increases in OT and PGF2 alpha responses are consistent with other reports that E2 increases OT and PGF2 alpha binding to myometrium; (iii) the E2 effect on OT response is probably independent of enhanced PG synthesis.