Effect of pregnancy-specific protein B on prostaglandin F2 alpha and prostaglandin E2 release by day 16-perifused bovine endometrial tissue

Five normal estrous cycling multiparous non-lactating Brahman cows were utilized to determine if pregnancy-specific protein B (PSPB) would alter prostaglandin F2 alpha (PGF) and prostaglandin E2 (PGE) synthesis/release by endometrial tissue. The uterine horn ipsilateral to the corpus luteum was excised on Day 16 of the estrous cycle. Endometrial tissue (200 mg wet wt) was cultured in Nutrient Mixture F-10 medium in a perifusion system. The tissue and medium were aerated with 95% O2: 5% CO2 and temperature was maintained at 39 degrees C. The medium flow rate was 100 microliters/min and fractions were collected at 20 min intervals. After a 120 min settling period, tissue culture continued with: 1) control (medium only); 2) 2 micrograms [Asu1,6]-oxytocin/ml medium for 1 h; 3) 4 or 8 micrograms PSPB/ml medium for 2 h; or 4) 4 or 8 micrograms PSPB/ml medium for 2 h plus 2 micrograms oxytocin/ml medium during the second h. Differences in PGF and PGE secretion rate were not found between 4 and 8 micrograms PSPB. Therefore, groups were combined and data were analyzed according to tissue not receiving PSPB (control); receiving PSPB and receiving PSPB plus oxytocin. A nonsignificant rise (p greater than 0.10) in PGF secretion was observed in response to PSPB and PSPB plus oxytocin above the control by the end of the perifusion period (263.7 +/- 41.7, 220.0 +/- 41.7 and 166.1 +/- 41.7 pg/(100 mg tissue/min), respectively). Treatment with PSPB alone elevated (p less than 0.05) PGE secretion rate above control by 100 and 160 min post-removal of PSPB treatment. Treatment with PSPB plus oxytocin elevated (p less than 0.05) PGE release above control by 20 min after starting oxytocin treatment and continued throughout the duration of the perifusion. Pregnancy-specific protein B plus oxytocin-induced PGE release was greater (p less than 0.05) than PSPB alone after initiating the oxytocin treatment until 20 min after removal of the treatments. However, no further differences between PSPB alone and PSPB plus oxytocin treatments were detected throughout the remainder of the perifusion period. It appears that PSPB tends to elevate PGF release and significantly elevates PGE release from Day 16 endometrial tissue.