PGFM response to exogenous oxytocin and determination of the half-life of oxytocin in nonpregnant mares

We investigated the half-life of oxytocin in reproductively normal mares an d the prostaglandin response after oxytocin administrations. Mares were giv en oxytocin, 10 or 25 iu, i.v., on the day of, or 2 days after, ovulation, and frequent jugular blood samples were collected for analysis of oxytocin and Prostaglandin F metabolite (PGFM) by RIA, Neither dose of oxytocin nor day of treatment affected the half-life of the exogenous oxytocin, which wa s determined to be 6.8 min. A significant increase in PGFM was observed wit hin 6 min of oxytocin administration and peak values were observed within 1 0 min. PGFM response after oxytocin administration on the day of ovulation appeared elevated compared to the response 2 days after ovulation.