The LH surge triggers drastic changes in the secretory function within the preovulatory follicles. It is well documented that LH regulates steroidogenesis and prostaglandin biosynthesis in granulosa, theca, and surrounding stromal cells. In several species, prostaglandin E2 (PGE2) has been considered an essential mediator for the LH action on the ovulatory processes. This concept is supported by the fact that inhibitors of prostaglandin synthesis such as in-domethacin can block ovulation in the rat, rabbit, and cow. Moreover, it has also been suggested that peptides such as endothelin and cytokines derived from the endothelium, fibroblasts, leukocytes, and follicular cells interact with LH and modify its action at the ovarian level.
The ovarian follicle has been reported to be a site of synthesis, reception, and action of endothelin-1 (ET-1), tumor necrosis factor a (TNFa), and interleukin-1p (IL-1p). These peptides directly affect the secretory function of theca and/or granulosa cells with a stimulatory or inhibitory effect on prostaglandin biosynthesis and steroidogenesis. Furthermore, ET-1 inhibits cAMP-mediated progesterone production in LH-stimulated granulosa cells in the rat and the pig. However, the specific roles of ET-1 and its interrelationships with LH, cytokines, and PGE2 during the preovulatory period in the bovine follicle still remain unclear. buy ortho tri-cyclen online
Therefore, we attempted to observe the local secretion of ET-1 and its effect on the release of steroid hormones and PGE2 in the theca layer of bovine mature follicles in vitro. The study was further extended to examine the possible interaction of ET-1 with LH, TNFa, and IL-1 p. For this purpose, a microdialysis system (MDS) was implanted into the theca layer of isolated bovine mature follicles, where the cells maintain the integrity of follicular structures, thus enabling a real-time observation of local release of substances that may play a role in cell-to-cell communication, as was originally done in freely moving pigs.