Role of endothelial cells in the steroidogenic activity of the bovine corpus luteum.

The LH surge triggers the ovulation of the preovulatory follicle and subsequent formation of a corpus luteum. After ovulation, microvessels from the thecal layer grow into the granulosa cell layer and a rapid process of neovascularization takes place, by midcycle endothelial cells constitute more than 50% of total corpus luteum (CL) cells. Concomitantly with the angiogenic process, luteal steroidogenic cells differentiate as they are surrounded by the growing capillary network. Luteal regression, on the other hand, is accompanied by changes in blood flow and vasculature. Thus, changes in the endothelial cell population within the CL closely consort with the functional changes occurring during various stages of the CL life span. This article summarizes data demonstrating that endothelial cells play an essential role in luteal steroidogenic activity by being involved in both luteotrophic and luteolytic processes.