Local release of steroid hormones, prostaglandin E2, and endothelin-1 from bovine mature follicles in vitro:: Effects of luteinizing hormone, endothelin-1, and cytokines

Local regulation of ovulation involves the interaction of LH and intrafollicular factors including steroids, prostaglandins, and peptides derived from endothelial cells, leukocytes, fibroblasts, and steroidogenic cells. To estimate the intrafollicular role of endothelin-1 (ET-1) and its possible interaction with LH, tumor necrosis factor alpha (TNF alpha), and interleukin-1 beta (IL-1 beta), a microdialysis system was implanted into the theca layer of preovulatory bovine follicles that were maintained in organ culture chambers. The effects of LH, ET-1,TNF alpha, and IL-1 beta on the local release of steroids, prostaglandin E-2 (PGE(2)), and ET-1 from the cells surrounding the implanted capillary membrane were investigated. Each preovulatory follicle (selected based on the concentrations of steroids and PGE(2)) was dissected from surrounding stromal tissue and implanted with 4 capillary dialysis membranes (control, LH, cytokines or ET-1, and LH+cytokine or LH+ET-1) into the theca layer. They were then incubated in organ culture chambers and perfused with Ringer's solution for 14 h after preperfusion for 2 h. The stimulation with LH (5 mu g/ml) between 4 and 6 h increased the release of progesterone (P-4), androstenedione (A), estradiol-17 beta (E-2), PGE(2) (p < 0.001), and ET-1 (p < 0.05). The infusion of ET-1 (250 ng/ml) between 8 and 10 h inhibited P-4 and A release but stimulated E-2 release (p < 0.05). The infusion of TNF alpha (100 ng/ml) between 8 and 10 h after LH exposure suppressed the release of A and E-2 (p < 0.05). IL-1 beta (10 ng/ml) between 8 and 10 h stimulated E-2 release but inhibited A release (p < 0.05). Moreover, ET-1 and cytokines clearly stimulated PGE(2) release (p < 0.05). ET-1 and TNF alpha induced further release of PGE, stimulated by LH (p < 0.05). Also, TNF alpha and IL-1 beta induced further release of ET-1 stimulated by LH (p < 0.05). These results show that ET-1 is released from the theca layer of mature bovine follicles in vitro and that it affects follicular steroids and PGE(2) secretion. The overall results suggest that interactions among ET-1, PGE(2), and cytokines may have key roles in a local intermediatory/amplifying system of the LH-triggered ovulatory cascade in the bovine preovulatory follicle.