Fine Structure and Progesterone Levels in the Corpus Luteum of the Pig During Pregnancy and after Hysterectomy1

Abstract

The corpora lutea of pregnant pigs were examined by electron microscopy at 28, 40, and 60 days following fertilization and compared to the corpora lutea from pigs hysterectomized for 40 and 60 days. Corpora lutea from a minimum of two animals were utilized at each interval. Progesterone analysis was performed on corpora lutea from each animal. The fine structure of granulosa lutein cells from the corpus luteum of pregnancy was similar to that of granulosa lutein cells in corpora lutea maintained for similar periods of time after hysterectomy. Furthermore, progesterone levels in the corpora lutea of these two groups of animals were generally similar during comparable stages. The cells showed fine structural features that are typical and characteristic of cells of steroid secretion. Compared with the published descriptions of the fine structure of granulosa lutein cells during the estrous cycle, the granulosa lutein cells during pregnancy and after hysterectomy contained a larger Golgi apparatus, more agranular endoplasmic reticulum organized as arrays of fenestrated cisternae, more granular endoplasmic reticulum, and an immensely larger number of membrane-limited dense bodies which were not acid phosphatase positive. The presence of considerable areas of granular endoplasmic reticulum in granulosa lutein cells from corpora lutea of pregnant and hysterectomized animals suggested an increased capacity for protein synthesis over that observed in the estrous cycle. It is possible that the dense bodies have a protein content related to relaxin.