DOMESTIC ANIMAL ENDOCRINOLOGY ELSEVIER Vol. 13(4):361-372, 1996 l/V zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA S/W DETECTION OF APOPTOSIS IN REGRESSING CORPUS LUTEUM OF PREGNANT SOW: EVIDENCE OF AN EARLY PRESENCE OF DNA FRAGMENTATION’ M.L. Bacci,2 A.M. Barazzoni, M. Forni, G. Lalatta Costerbosa Department of Veterinary Morphology and Physiology and Animal Production University of Bologna, Bologna, Italy Received August zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ 1, 1995 Luteolysis has been shown to be correlated with apoptosis in rats, sheep, and cows. In pigs, apoptosis has already been demonstrated as regards atretic follicles. The present study has been conducted to evaluate whether apoptosis occurs during corpora lutea regression in the pregnant pig and to investigate the temporal relationship between apoptosis and functional luteolysis. The apop- totic process has been studied through the research of oligonucleosome fragmentation by means of classical electrophoresis methods and by in situ detection on histological luteal sections. The latter method allows the identification of apoptosis and the localization of apoptotic cells. Pregnant sows were cloprostenol (PGF,, analog) treated and ovariectomized 0, 6, 12, 24, 48, and 72 hr after treatment. Corpora lutea were utilized for progesterone and DNA extraction and in situ evaluation of apoptosis. Clear evidence of apoptosis was seen earlier with the in situ technique (6 hr for stromal tissue, 12 hr for luteal cells) than with the classical method (24 hr). Apoptosis was, however, apparent after plasma and tissue progesterone had reached basal levels. In conclusion, these results are consistent with the hypothesis that apoptosis occurs during Iuteolysis in pigs. Moreover, the data obtained with the in situ technique made it possible to identify signs of structural regression in stromal tissue first than in parenchymal cells. A two-stage activation of apoptosis has been discussed to explain structural changes that occur during luteolysis after cloprostenol treatment in swine corpora lutea. INTRODUCTION In domestic species, as in pigs, corpus luteum (CL) regression is dependent on the uterine release of prostaglandin FZol (PGF,,) at appropriate times during the estrous cycle or pregnancy (14). The cyclic regression of this particular endocrine gland is one of its most intriguing features, as it allows repeated opportunities for follicular growth, ovula- tion, and pregnancy. CL regression consists of two processes: functional and structural luteolysis. Functional luteolysis refers to the suppression of progesterone (PJ synthesis and secretion, while structural luteolysis refers to the physical elimination of CL from the ovaries. The rapid effects of PGF,, on functional luteolysis in pigs are well established (5,6). However, the cellular mechanisms associated with luteolysis are unclear and the results of in vitro experiments with pigs (7) and other mammalian species show conflict- ing evidence, as exhaustively reviewed by Pate in 1994 (8). In particular, PGF,, did not directly cause cellular degeneration in rat (9) or bovine (10,ll) luteal cells in in vitro culture. The different effects of PGF,, observed in vitro and in vivo may be explained by the hypothesis that additional mechanisms are required for complete luteolysis (7,8). Recently much evidence has been reported on the involvement of the immune system in luteolysis (11-13). Apoptosis, that is programmed cell death, has been shown to occur in 0 Elsevier Science Inc. 1996 0739-7240/96/$15.00 655 Avenue of the Americas, New York, NY 10010 PII SO739-7240(96)00049-5