Abstract: 495

DEXAMETHASONE INCREASES OXYTOCIN (OT) INDUCED PGF₂ RELEASE WITHOUT AUGMENTING ENDOMETRIAL OT RECEPTOR CONCENTRATIONS IN LATE PREGNANT COWS.

A-R Fuchs^{1 *}, MJ Fields^{2 *}
Dept of OB/GYN, Cornell Univ Medical College, New York, New York ¹
Animal Science Dept, Univ of Florida, Gainesville, Florida ²

We have previously shown that oxytocin (OT) induces cyclooxygenase 2 (COX-2) expression in bovine intercaruncular endometrium (Biol Reprod 1999; 60:341). In the present study we examined the effect of dexamethasone (DEXA) pretreatment on OT induced PGF₂ release and on OT receptor (OTR) and OTR mRNA concentrations in endometrium and other uterine tissues of late pregnant cows. Two groups of 4 crossbred Angus-Brahman cows were used on day 275 of gestation in these experiments; 4 cows were given 30 mg DEXA im and 4 received the vehicle. OT (100 IU) was injected iv before and 24 h after administration of DEXA or vehicle. Blood samples were collected for 3 h with 15 min intervals beginning 30 min before OT injection. Plasma 13,14-dihydro-15-keto PGF₂ metabolite (PGFM) was measured in all samples. After completion of the second OT challenge the cows were exsanguinated and uterine tissues collected for ligand binding (OT) and RNA extraction for OTR mRNA measurement. Results: DEXA pretreatment resulted in greatly increased PGFM response to OT in comparison to values observed before DEXA injection or in controls. Basal PGFM levels were also somewhat increased in the DEXA treated cows. OTR concentrations and OTR mRNA in DEXA treated cows were not significantly increased in endometrium, myometrium, caruncles, cotyledons or fetal membranes in comparison to controls. The DEXA induced augmentation of the PGFM response to OT may therefore be exerted on endometrial OTR signaling pathway.

    This abstract is being presented on Tuesday, August 3 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.