Uterine contractility in nonpregnant mares

Uterine contractility has been studied by intrauterine pressure transducers - balloons or catheter tip pressure transducers - electromyography (EMG), transrectal ultrasound, and recently, by scintigraphy. Maximal uterine cont ractility was seen in ultrasonography during the late luteal phase (days 13 to 14), at the time of the expected luteolysis. Also in EMG, frequent spik es of short duration alternating with short periods of inactivity were repo rted during luteolysis. Total electrical activity was higher in dioestrus t han in oestrus. Oestrus was characterised by shorter spikes of higher inten sity separated by longer periods of inactivity as compared to dioestrus. In trauterine infusion of bacteria increased myometrial electrical activity fo r 5 hours in ail mares and for 18 hours in healthy mares resistant to uteri ne infections. Resistant mares exhibited greater uterine activity 10 to 20 h after inoculation than mares susceptible to uterine infections. Inseminat ion (Ai) caused spikes of higher amplitude and more frequent active phases for 2 to 7 hours as recorded by EMG. Scintigraphy showed how Al induced ute rine contractions which were most frequent during the first 10 to 30 min. R ectal palpation caused a transient increase in myometrial activity. Oxytoci n increased myometrial activity at ail stages of the cycle and prostaglandi n F-2 alpha and its synthetic antagonists in cycling and steroid-treated ma res, alpha2-agonists, detomidine, xylazine, and romifidine increased intrau terine pressure and electrical activity. Propantheline and acepromazine sup pressed myometrial activity.