Bioscientifica Proceedings

The formation, normal function and destruction of corpora lutea are essential features of normal reproduction. Although the formation of corpora lutea from follicles is largely dependent on pituitary gonadotrophins, the process of luteolysis is locally regulated and poorly understood. The corpus luteum consists of several steroidogenic and nonsteroidogenic cell types that interact with each other in a paracrine manner. Under cell culture conditions, large luteal cells that stem from follicular granulosa cells can be identified easily under the microscope and collected individually for single cell RT-PCR. As each of the 120 large luteal cells express the gene encoding 3β-hydroxysteroid dehydrogenase, it appears that all large luteal cells are steroidogenic. large luteal cells also express the oestrogen receptor gene and as they are known to produce oestradiol, it can be concluded that the steroid acts in an auto- or intracrine manner in large luteal cells. Since we showed previously that oestradiol stimulates progesterone release under in vitro and in vivo conditions, it can be concluded that the steroid is an important intraluteally acting luteotrophic signal. At the time of luteal regression, macrophages invade the corpora lutea and their cytokine products, particularly tumour necrosis factor a (TNFα), appear to be involved in reduced steroid secretion. Indeed, TNFα inhibits production of progesterone and oestradiol from cultivated luteal cells In sows, oestradiol is a strong luteotrophic factor and the production of oestradiol and of its receptor is downregulated by TNFα. Thereby, TNFα not only exerts direct luteolytic effects but also prevents the luteotrophic effects of oestradiol. Hence, it has an anti-luteotrophic action. In most species, functional luteolysis is accompanied by morphological regression of the corpus luteum. This structural luteolysis also appears to involve TNFα, as we have shown in pigs that expression of TNFα gene is high during luteolysis. Furthermore, TNFα stimulates programmed cell death (apoptosis) in luteal cells kept under culture conditions.

© 1997 Journals of Reproduction and Fertility Ltd