Luteotrophic and luteolytic interactions between bovine small and large luteal-like cells and endothelial cells

Endothelial cells, the most abundant cell type in the bovine CL, were shown to establish intercellular contact with steroidogenic cells of the CL. Two experimental models were used to study the involvement of endothelial cells in luteal cell function; 1) luteal slices in which the integrity and communication between the different cells were maintained and 2) pure large and small luteal-like cells, cultured separately or co-cultured with endothelial cells. The luteolytic effect of prostaglandin (PG) F(2α) was examined in these two models. Treatment with PGF(2α) did not alter P₄ secretion stimulated by LH in young (2-4-day-old) CL slices, whereas, in slices from mature (6-12 days old) CL, PGF(2α) significantly reduced (by 40%) the stimulatory effect of LH on P₄ secretion. In pure large luteal- like cells, the effect of forskolin plus PGF(2α) on P₄ secretion did not differ from forskolin given alone after 3 or 24 h of incubation. However, when co-cultured with endothelial cells, PGF(2α) significantly inhibited forskolin stimulation. Endothelial cells significantly stimulated P₄ production from large luteal-like cells only. This effect may be attributed to the action of PGI₂ secreted by endothelial cells. In summary, endothelial cells may play an essential role in luteal functions by being involved in both luteotrophic and luteolytic processes.