Evaluation of biochemical and structural changes in individual porcine corpora lutea during prostaglandin F2 alpha-induced luteolysis with an in vivo implant system.

To date, no in vitro system has been devised to allow the study of both the functional and the structural regression of luteal cells in response to prostaglandin (PG) F2 alpha. This study describes the use of a novel intraluteal PGF2 alpha implant system that results in the death of individual corpora lutea (CL), while surrounding CL on the same ovary remain fully functional. By this technique, it was possible to study both the functional and the structural regression of individual CL in vivo, without the confounding effects resulting from the systemic injection of PGF2 alpha. Biochemical measurements of individual CL included progesterone concentration, protein kinase C activity, and diacylglycerol levels. Structural measurements included luteal weight and the protein:DNA ratio, which was used to estimate cell size. Further, the determination of large luteal cell size was accomplished directly via light microscopy. Nonpregnant gilts were injected with 5 mg of estradiol benzoate every 12 hr from 8:00 a.m. on Day 11 to 8:00 a.m. on Day 13 to prevent uterine PGF2 alpha secretion. At 7:00 a.m. on Day 13, CL on one ovary were selected at random to receive PGF2 alpha-implants (n = 4) or implant material only (n = 4), whereas the remaining CL on that ovary served as unimplanted controls. The other ovary was removed at the point, and the CL on that ovary served as 0-hr controls. Gilts were relaparotomized at 3, 6, 12, and 24 hr after CL implantation, the PGF2 alpha-implanted ovary was removed, and individual CL were evaluated. PGF2 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 PGF2 alpha-treated CL at 12 and 24 hr. Moreover, this change in the protein:DNA ratio (cell size) was consistent with the reduced diameter (P < 0.05) of the large luteal cell in the PGF2 alpha-treated CL. Protein kinase C activity and diacylglycerol concentrations did not change (P > 0.10) and therefore appear to be unassociated with either functional or structural changes in the PGF2 alpha-treated CL. Contrary to in vitro culture studies, the results of our in vivo study demonstrate no clear role for protein kinase C in the PGF2 alpha-induced luteolytic process.(ABSTRACT TRUNCATED AT 400 WORDS)