Biology of Reproduction, Vol 22, 259-268, Copyright © 1980 by Society for the Study of Reproduction

Effects of in vivo Prostaglandin F₂ Administration on in vitro Progesterone Synthesis by Bovine Corpora Lutea

¹ Department of Veterinary Biosciences, University of Illinois, Urbana, Illinois 61801

The effects of i.m. injections of 25 mg prostaglandin F₂ (PGF₂) on peripheral progesterone concentrations, luteal progesterone concentrations and in vitro progesterone synthesis were determined. Heifers with a history of normal estrous cycles were treated with PGF₂ on Day 12 or 13 and corpora lutea were surgically removed 0, 2, 4 or 8 h later (5 animals/time period). Corpora lutea were sliced and aliquots representing 100-200 mg tissue were removed to determine tissue concentrations of progesterone. Dispersed cell preparations were prepared from remaining tissue. Three ml of cells (1 x 10⁶ cells/ml) were incubated for 1 h with 0, 0.1, 1 or 10 ng luteinizing hormone (LH)/ml and 0, 10, 100 or 1000 ng PGF₂/ml in a 4 x 4 factorial design. Plasma concentrations of progesterone were decreased (P<0.05) within 2 h of injection of PGF₂. The progesterone concentration of corpora lutes removed at 0 h was 65 ± 7 µg/g tissue (mean ± SEM) and was greater (P<0.01) than that observed at 2, 4 or 8 h (39 ± 3, 33 ± 3 and 33 ± 2 µg/g, respectively). In the absence of LH or PGF₂ in vitro, progesterone synthesis by corpora lutea removed at 0, 2 or 4 h postinjection was similar and was approximately twice that observed by corpora lutea removed at 8 h. Nevertheless, LH increased (P<0.01) progesterone synthesis by corpora lutea removed at all time periods. PGF₂ also increased (P<0.01) net progesterone accumulation. However, the response of corpora lutea to PGF₂ removed at 8 h was less than that observed at 0, 2 or 4 h indicating a corpus luteum removal time by PGF₂ interaction (P<0.01). These data suggest that in vivo administration of PGF₂ had effects on plasma and tissue progesterone concentrations before diminution of the in vitro steroidogenic response of corpora lutea to LH or PGF₂.

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ACKNOWLEDGEMENTS We are grateful to David Faber, James Nuessen and Terry Ryan for their excellent assistance. We wish to thank The Upjohn Co. and Dr. James Lauderdale for the PGF₂ employed in this study. We also thank the National Pituitary Agency, NIAMDD, for the bovine LH used as standards in the LH radioimmunoassay. We are indebted to Dr. Gordon Niswender for the LH antiserum. Validation of the progesterone antiserum was conducted utilizing laboratory facilities under the direction of Dr. William Hansel with the excellent technical assistance of Raymond Saatman and Stella Vincent.