CHANGES IN PERIPHERAL CONCENTRATIONS OF 13,14-DIHYDRO-15-KETO-PROSTAGLANDIN F2-ALPHA INDUCED BY PROGESTERONE IN SWINE

This experiment was designed to examine the effects of progesterone on endogenous and oxytocin-induced secretion of prostaglandin F-2 alpha (PGF(2 alpha) in sows. Peripheral concentrations of 13, 14-dihydro-15- keto-PGF(2 alpha2 alpha), (PGFM) were used as an indirect measure of u terine PGF(2 alpha), secretion. Eight sows received twice daily inject ions of progesterone (160 mg/injection) on d 1 to 5 after estrus. Anot her eight sows received comparable injections of a corn oil injection vehicle. Each sow then received i.v. injections of oxytocin (30 IU) on d 10, 12, and 15 after estrus. Concentrations of PGFM were determined in jugular venous blood samples collected at -60, -45, -30, -15, 0, 2 , 5, 10, 15, 30, 45, 60, 90, and 120 min after each oxytocin injection . The mean concentrations of PGFM in samples collected before injectio n of oxytocin (baseline), the magnitude of the PGFM response to oxytoc in, and the area under the PGFM response curve (AUC) were calculated f or the three oxytocin challenges administered to each sow. Baseline, m agnitude, and AUC were low on d 10 after estrus and similar for the tw o treatment groups. On d 12 baseline, magnitude, and AUC remained low in the control sows; however, all three response variables increased i n sows that received progesterone. By d 15, all three variables were h igh and similar in both treatment groups. In conclusion, progesterone, administered early in the estrous cycle, seems to promote premature s ecretion of PGF(2 alpha), as indicated by the high basal concentration s of PGFM observed before injection of oxytocin on d 12. This may be d ue to the apparent increase in uterine secretory responsiveness to oxy tocin observed at this time.