The objective of the present study was to investigate the influence of progesterone on prostaglandin synthesis by the corpus luteum (CL). Corpora lutea were obtained from dairy cows on days 4,6,10, and 18 of the estrous cycle, dissociated. and placed in serum-free culture. The addition of luteinizing hormone (LH) resulted in a slight, but nonsignificant (p > 0.05), increase in levels of 6-keto-PGF1α, and had no effect on PGF2α. Progesterone treatment caused a significant, dose-dependent decrease in both PGF2α and 6-keto-PGF1α in 6-day and 10-day corpora lutea, but not in 4-day or 18-day corpora lutea. In the 6- and 10-day corpora lutea, progesterone treatment resulted in a greater inhibition of PGF2α than 6-keto-PGF1α production. Therefore, progesterone treatment brought about an increase in the 6-keto-PGF1α to PGF2α ratio in these cells (12.9 vs. 21.3). It is concluded from these studies that progesterone can modulate luteal prostacyclin and PGF2α synthesis, suggesting an interaction of progesterone and prostaglandin production within the corpus luteum.
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