Ultrastructural Observations On The Opossum Corpus-Luteum Late In Pregnancy

Corpora lutea of the opossum ovary late in pregnacy consist of a heterogenous population of lutein cells. Three different categories of cells are observed as determined by their ultrastructural features. The cytoplasm of one category, which are few in number, is characterized by an abundance of smooth endoplasmic reticulum and lacks for the most part discrete electron dense granules. The most abundant population of cells is characterized by clusters of electron dense granules and scattered profiles of rough endoplasmic reticulum. A third category is present that exhibits ultrastructural features characteristic of both previous cell populations. These three forms of structurally diverse large cells are though to represent a broad spectrum of a single cell type rather than independent populations. It is believed that one form transitions to another dependent on the reproductive status of this species.