Ultrastructural Dynamics During Corpus Luteum Development and Growth

Abstract

The corpus luteum is an endocrine organ (Fig. 11-1) that develops from the ruptured follicle at ovulation. During its functional life span it grows, and then regresses to a small connective tissue scar (corpus albicans) within the ovarian stroma. The corpus luteum secretes the steroid hormone progesterone. In primates, the corpus luteum is also a source of estrogens and prostaglandin PGF_2α, and in the human, pig, and rat it also secretes relaxin (see also Chapter 12). Progesterone has a number of biological effects on the reproductive organs of the female during the estrous cycle, and all or part of pregnancy, depending on the species. Inadequate development and growth, and hence function, of the corpus luteum accounts for significant loss of mammalian embryos during early pregnancy, and so there is much interest in understanding mechanisms influencing the formation, growth, and function of the corpus luteum. An understanding of these mechanisms might also identify new approaches to regulate fertility. This chapter summarizes quantitative morphological information on corpus luteum development and growth that has accumulated over the past decade. Particular attention is focused on ultrastructural-functional relationships in the luteal cell. This information is due to the recent description [1] and use of stereolo- gical methods to quantitate biological structures. Most of the description here relates to work completed on the pregnant rat, as this is the most common experimental animal used and such quantitative data are not yet available, nor probably possible, from human studies.