Prostacyclin, Prostaglandin F2α and Progesterone Production by Bovine Luteal Cells during the Estrous Cycle 1

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Abstract
Corpora lutea (CL) were collected from Holstein heifers on days 5, 10, 15 and 18 (5/day) of the estrous cycle. Dispersed luteal cell preparations were made and 106 viable luteal cells were incubated with bovine luteinizing hormone (LH) and different amounts of arachidonic acid in the presence and absence of the prostaglandin (PG) synthetase inhibitor, indomethacin. The concentrations of progesterone, PGF2.alpha. and 6-keto-PGF1.alpha., the stable inactive metabolite of prostacyclin (PGI2), were measured. DAy 5 CL had the greatest initial content of 6-keto-PGF1.alpha. (1.01 .+-. 0.16 ng/106 cells), and synthesized more 6-keto-PGF1.alpha. (2.55 .+-. 0.43) than CL collected on Days 10 (0.57 .+-. 0.11), 15 (0.08 .+-. 0.05) and 18 (0.19 .+-. 0.03) during a 2-h incubation period. Arachidonic acid stimulated the production of 6-keto-PGF1.alpha. by days 10, 15 and 18 luteal tissue. PGF2.alpha. was produced at a greater rate on day 5 (0.69 .+-. 0.17 ng/106 cells) than on days 10 (0.06 .+-. 0.01), 15 (0.04 .+-. 0.02) and 18 (0.08 .+-. 0.01). Arachidonic acid stimulated and indomethacin inhibited the production of PGF2.alpha., in most cases. The initial content of 6-keto-PGF1L.alpha. was higher than that of PGF2.alpha. on all days of the cycle and more 6-keto-PGF1.alpha. was synthesized in response to arachidonic acid addition. The ratio of 6-keto-PGF1.alpha. content to PGF2.alpha. content was 4.39, 2.30, 1.25 and 1.13 on days 5, 10, 15 and 18, respectively. Progesterone production during 2 h incubation decreased as the age of the CL advanced and the concentration of PGI2 declined. Concentrations (ng/106 cells) were 128 .+-. 12, 87 .+-. 18, 38 .+-. 9 and 54 .+-. 7 on Days 5, 10, 15 and 18, respectively. PGI2 may play an important luteotropic role, particularly during the first 10 days of the bovine estrous cycle.