EVALUATION OF BIOCHEMICAL AND STRUCTURAL-CHANGES IN INDIVIDUAL PORCINE CORPORA-LUTEA DURING PROSTAGLANDIN F-2-ALPHA-INDUCED LUTEOLYSIS WITHAN IN-VIVO IMPLANT SYSTEM

To date, no in vitro system has been devised to allow the study of bot h the functional and the structural regression of luteal cells in resp onse to prostaglandin (PG) F-2 alpha. This study describes the use of a novel intraluteal PGF(2 alpha implant system that results in the dea th of individual corpora lutea (CL), while surrounding CL on the same ovary remain fully functional. By this technique, it was possible to s tudy both the functional and the structural regression of individual C L in vivo, without the confounding effects resulting from the systemic injection of PGF(2 alpha). Biochemical measurements of individual CL included progesterone concentration, protein kinase C activity, and di acylglycerol levels. Structural measurements included luteal weight an d the protein:DNA ratio, which was used to estimate cell size. Further , the determination of large luteal cell size was accomplished directl y via light microscopy. Nonpregnant gilts were injected with 5 mg of e stradiol benzoate every 12 hr from 8:00 a.m. on Day 11 to 8:00 a.m. on Day 13 to prevent uterine PGF(2 alpha) secretion. At 7:00 a.m. on Day 13, CL on one ovary were selected at random to receive PGF(2 alpha)-i mplants (n = 4) or implant material only (n = 4), whereas the remainin g CL on that ovary served as unimplanted controls. The other ovary was removed at that point, and the CL on that ovary served as 0-hr contro ls. Gilts were relaparotomized at 3, 6, 12, and 24 hr after CL implant ation, the PGF(2 alpha)-implanted ovary was removed, and individual CL were evaluated. PGF(2 alpha)-implanted CL exhibited a decline (P < 0. 05) in progesterone concentrations at 12 and 24 hr and a decline (P < 0.05) in weight at 24 hr when compared with control CL (implant-only, unimplanted, and 0-hr control CL). Furthermore, the protein:DNA ratio was reduced (P < 0.10) in the PGF(2 alpha)-treated CL at 12 and 24 hr. Moreover, this change in the protein:DNA ratio (cell size) was consis tent with the reduced diameter (P < 0.05) of the large luteal cell in the PGF(2 alpha)-treated CL. Protein kinase C activity and diacylglyce rol concentrations did not change (P > 0.10) and therefore appear to b e unassociated with either functional or structural changes in the PGF (2 alpha)-treated CL. Contrary to in vitro culture studies, the result s of our in vivo study demonstrate no clear role for protein kinase C in the PGF(2 alpha)-induced luteolytic process. In contrast, our study does temporally link a decline in luteal progesterone concentrations with a decrease in the size of large luteal cells.