Effect of endothelin-1 on bovine luteal cell function: Role in prostaglandin F-2 alpha-induced antisteroidogenic action

Endothelin-1 (ET-1), a vasoactive peptide, is synthesized and secreted by endothelial cells. In the bovine corpus luteum (CL), endothelial cells constitute a major proportion (53.5%) of total CL cells. This study was designed to examine the effects of ET-1 on bovine luteal cell functions and its involvement in the action of PGF(2 alpha). To better define the cells implicated in this process, we used CL slices, whole CL-derived cells, and steroidogenic large (LLC) and small (SLC) luteal-like cells. High affinity binding sites for ET-1 (K-d, similar to 0.3 x 10(-9)) were present in both steroidogenic luteal cells. The binding affinity of ET-1 was 3 orders of magnitude higher than that of ET-3, and a selective ET(A) receptor antagonist (BQ123) competed similarly to ET-1, suggesting the presence of ET(A) receptors. The lack of effect of ET-3 on CL-derived cells further supported this conclusion. Both basal progesterone secretion and bovine LH (5 ng/ml)-stimulated progesterone secretion from CL-derived cells were significantly inhibited by ET-1 in a dose-dependent manner, whereas preincubation of these cells with ET(A) receptor antagonist prevented the inhibitory effect of added ET-1. Incubation of LLC with 10(-8) M ET-1 inhibited their progesterone secretion (114.8 vs. 176.7 ng/10(5) cells . 20 h; P < 0.05). On the other hand, ET-1 did not affect progesterone production from SLC despite the presence of ET-binding sites. PGF(2 alpha) only inhibited LH-stimulated progesterone secretion by luteal slices. This antisteroidogenic effect of PGF(2 alpha) could be prevented by the addition of a selective ET(A) receptor antagonist. Luteal tissue and microvascular endothelial cells isolated from bovine CL produced ET-1; in contrast, the peptide was undetectable in the culture medium or in cell extracts of either LLC or SLC. These data support the concept that ET-1 may play a paracrine regulatory role in bovine luteal function and propose a novel role for this peptide in mediating PGF(2 alpha)-induced luteal regression.