Luteotrophic and luteolytic actions of ovarian peptides

Corpora lutea of all species investigated so far, including the human, produce oxytocin and a variety of other regulatory peptides. The role of these peptides is largely unknown. The subtypes of large luteal cells are able to produce tumour necrosis factor (TNF) and at the end of the luteal phase TNF-producing macrophages invade the aged corpus luteum, indicating that this cytokine may be involved in the process of luteolysis. The present contribution reviews briefly the known functions of oxytocin and substance P in the corpus luteum and then elaborates the possible involvement of luteal and macrophage TNF during luteolysis. Oxytocin applied to intact corpus luteum stimulates the secretion of progesterone and oestradiol. The stimulation of progesterone secretion by oxytocin is due to the stimulated oestrogen production. TNF, when tested in vitro, inhibits both luteal cell progesterone and oestradiol production. The TNF-mediated inhibition of aromatase activity therefore prevents the luteotrophic effects of a variety of peptides including oxytocin. This appears to be the mechanism by which TNF induces luteolysis.