OXYTOCIN ENHANCES CLEARANCE OF RADIOCOLLOID FROM THE UTERINE LUMEN OF REPRODUCTIVELY NORMAL MARES AND MARES SUSCEPTIBLE TO ENDOMETRITIS

The effects of oxytocin on the percentage of technetium 99m albumin colloid (Tc-99m-muAA), cleared from the uterine lumen was measured in 13 mares. Scintigraphy was performed during 4 consecutive oestrous cycles, on Day 3 of oestrus during Cycles one and 3 and 48 h after ovulation during Cycles 2 and 4. Oxytocin (20 iu) was given i.v. after the initial scintigraphy image during Cycles 3 and 4. Seven multiparous mares (Group 1) were classified as 'susceptible' and 6 mares (2 nulliparous and 4 multiparous; Group 2) were classified as 'resistant' to endometritis. All mares cleared >90% of Tc-99m-muAA within 30 min of oxytocin injection. When no drug was given, Group 1 mares cleared negligible amounts of radiocolloid (<5%) and Group 2 mares cleared 50-80%. No mares showed signs of colic after oxytocin administration. It is concluded that oxytocin enhances uterine clearance of radiocolloid and may be useful for treating mares exhibiting impaired uterine clearance.