Abstract
The major objective of this experiment was to determine whether the bovine placenta could be stimulated to secrete progesterone, since the bovine placenta secretes little progesterone when the corpus luteum is functional. Secondly, we wanted to determine whether reported abortifacients or progesterone or estrogen receptor antagonists affected bovine placental prostaglandin secretion. The ovine placenta secretes half of the circulating progesterone at day 90 of pregnancy and PGE 2 appears to regulate ovine placental progesterone secretion. Calcium has been reported to regulate placental progesterone secretion in cattle. Diced 186–245-day placental slice explants from six Brahman and six Angus cows were incubated in vitro at 39.5 °C under 95% air: 5% CO 2 at pH 7.2 in 5 ml of M-199 for 1 h in the absence of treatments and for 4 and 8 h in the presence of treatments. Treatments were: vehicle; R24571; compound 48/80; IP 3; PGE 2; CaCl 2; cyclosporin A; lipopolysaccharide (endotoxin) from Salmonella abortus equi., enteriditis, and typhimurium; monensin; ionomycin; arachidonic acid; mimosine; palmitic acid; progesterone, androstenedione; estradiol-17β; A23187; RU-486; or MER-25. Jugular and uterine venous plasma and culture media were analyzed for progesterone, PGE 2 and PGF 2α by radioimmunoassay (RIA). Plasma hormone data were analyzed by a One-Way Analysis of Variance (ANOVA). Hormone data in culture media were analyzed for breed and treatment effects by a Factorial Design (2 breeds, 2-range of days, 21 treatments) for ANOVA (2 × 2 × 21). Since hormone data secreted by placental tissue in vitro did not differ ( P≥0.05) by breed or range of days of pregnancy, data were pooled and analyzed by a One-Way ANOVA. Concentrations of PGE 2 in uterine venous blood were two-fold greater ( P≤0.05) in Angus than Brahman cows. PGE 2 and PGF 2α in vehicle controls increased from 4 to 8 h ( P≤0.05), but not progesterone ( P≥0.05). Progesterone in culture media treated with RU-486 increased ( P≤0.05) at 4 and 8 h compared to vehicle controls and was not affected by other treatments ( P≥0.05). Concentrations of PGE 2 in media at 4 and 8 h were lower ( P≤0.05) when compared to controls except treatment with PGE 2 at 4 and 8 h and RU-486 at 8 h ( P≥0.05). PGF 2α was increased ( P≤0.05) by RU-486 at 8 h and no other treatment affected PGF 2α at 4 or 8 h ( P≤0.05). In conclusion, modulators of cellular calcium signalling pathways given alone do not affect bovine placental progesterone secretion at the days studied and progesterone receptor-mediated events appear to suppress placental progesterone, PGF 2α, and PGE 2 secretion in cattle. In addition, PGE 2 does not appear to regulate bovine placental progesterone secretion when the corpus luteum is functional and bacterial endotoxin does not appear to affect bovine placental secretion of PGF 2α or PGE 2.
Published Version
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