Effects of instrumentation on myometrial activity in the oophorectomized ewe

The influence of an intrauterine pressure catheter on electrical myometrial activity (EMG) was investigated in chronically instrumented oophorectomized sheep. The EMG of non-catheterized (NC) ewes (n = 4) was characterized by long-lasting but infrequently occurring bursts of electrical activity, whereas the EMG of catheterized (C) ewes (n = 4) showed short and frequent bursts. Intra-arterial administration of 0.1 mg of 17 beta-estradiol (E2) was followed in C and NC ewes by an increase in myometrial activity after an initial silent period. E2 did not essentially change the pattern of long and short bursts in either group. Intravenous administration of the prostaglandin-synthesis inhibitor naproxen changed the EMG pattern in the C ewes, both before and after E2, to a pattern resembling the EMG of NC ewes. The results of this study indicate that electrical myometrial activity is markedly influenced by the presence of an intrauterine pressure catheter, probably due to enhanced prostaglandin synthesis.