Luteal regression in the primate: Different forms of cell death during natural and gonadotropin-releasing hormone antagonist or prostaglandin analogue-induced luteolysis

Morphological changes in the corpus luteum following natural and induced lu teolysis in the marmoset were investigated by light and electron microscopy . Functional corpora lutea were studied in the mid and late luteal phase, n aturally regressed corpora lutea in the early and late follicular phase, an d corpora lutea induced to regress by administration of GnRH antagonist or prostaglandin F-2 alpha analogue in the midluteal phase. Natural luteolysis was associated with lutein cell atrophy, condensation of cytoplasmic inclu sions and organelles, and accumulation of lipid. GnRH antagonist treatment resulted in aggregations of smooth membranes and myelin-like bodies in the cytoplasm of the lutein cells together with complex aggregations of degener ative cells. After prostaglandin treatment, the lutein cells contained nume rous small and large vesicles; as the degenerative changes advanced, these vesicles coalesced into alveolar-type vacuoles, and nuclei involuted. These results show that in the marmoset, natural luteolysis and the two luteolyt ic treatments reveal different forms of lutea( degeneration and cell death, none of which fit the ultrastructural criteria for apoptosis. More emphasi s needs to be placed on understanding these predominant nonapoptotic Corms of cell death in order to elucidate the process of luteolysis in the primat e.