title: Evidence for an intrinsic control of myometrial contractile periodicity in sheep during pregnancy.
abstract: 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.
authors.affiliation: Samuel Lunenfeld Research Institute, Department of Obstetrics and Gynecology, Mount Sinai Hospital, Canada.
authors.forename: S J
authors.initials: SJ
authors.lastname: Lye
mesh_terms: D000818:Animals; D015237:Dinoprost / Q000031:analogs & derivatives / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D009215:Myometrium / Q000187:drug effects / Q000502:physiology* / Q000637:transplantation; D010121:Oxytocin / Q000494:pharmacology; D010507:Periodicity; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011453:Prostaglandins / Q000502:physiology*; D012756:Sheep / Q000097:blood / Q000502:physiology*; D014590:Uterine Contraction / Q000502:physiology*
chemical_list: D011453:Prostaglandins; C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D010121:Oxytocin; D015237:Dinoprost