Submission Number: KIM-4-35-18

Abstract Number: 609

OXYTOCIN CAUSES PROSTAGLANDIN F₂ RELEASE FROM EQUINE ENDOMETRIUM IN A DAY-, DOSE-, AND TIME-DEPENDENT MANNER.

Kimberly M Smith*, Christa Y Behrendt-Adam*, Michelle M Ward, Mary H Adams* and Karen J McDowell*

Department of Veterinary Science, University of Kentucky, Lexington, KY, USA ¹

Abstract:
The endogenous luteolytic factor in nonpregnant mares is prostaglandin F₂ (PGF) produced by the uterus; however, information regarding control of uterine PGF is lacking. We demonstrated that uterine endometrium of mares produces oxytocin (OT) (Behrendt et al., BOR Suppl 1:134,1997) and that OT mRNA abundance varies with day of the estrous cycle and early pregnancy (Behrendt-Adam et al., DAE 16:183, 1999) and with administration of steroids (Behrendt-Adam et al., JRF, in press). In addition, OT caused release of PGF in a time-dependent manner in endometrium obtained at the expected time of luteolysis (Behrendt-Adam et al., BOR Suppl 1:205,1999). The purpose of this experiment was to determine if OT-stimulated PGF release by endometrial explants was affected by 1) dose of OT, 2) day of the estrous cycle, and 3) time of incubation. Endometrial biopsies were collected at estrus (n=6) and at days 11, 13 and 15 (n=4/day) after ovulation. Tissues (50 mg/plate, in duplicate) were incubated in 1 ml minimum essential medium (MEM) for 30 minutes at 37C. The medium was discarded, and 1 ml MEM containing 0 or 10^-10 to 10^-5 M OT (log doses) was added . Cultures were incubated for 30 or 60 min, and concentration of PGF in the medium was determined by RIA. There were significant effects of Day, Dose, Time, Day*Time, and Day*Dose*Time. Day 15 endometrium produced significantly higher PGF concentrations than any other day tested. When day 15 endometrium was incubated for 60 min, all doses of OT resulted in greater concentrations of PGF than no OT, and 10^-10 M OT resulted in greater PGF concentrations than any other dose tested (p<0.0001). These data demonstrate that OT causes PGF release from equine endometrium in vitro in a day, time and dose-dependent manner. In mares, endometrial OT may interact with endometrial PGF to cause luteolysis in a manner similar to that of luteal OT and endometrial PGF in ruminants. Supported by The Grayson-Jockey Club Research Foundation, Kentucky Opportunity Fellowship (KM Smith), and The Geoffrey C. Hughes Foundation. .

Keywords: uterus, horse, oxytocin, prostaglandin, luteolysis

This abstract is being presented at: 8:00 AM in session:
Uterus/Oviduct II