Chicken gonadotropin-releasing hormones enhance soluble and insoluble fibronectin production by granulosa cells of the domestic fowl in vitro

Experiments were conducted in vitro to examine the effect of two chicken gonadotropin-releasing hormones, cGnRH-I ([Gln(8)]-GnRH) and cGnRH-II ([His(5),Trp(7),Tyr(8)]-GnRH), on fibronectin (soluble and insoluble) production by chicken granulosa cells isolated from the largest (F1; about 35 mm in diameter), and third largest (F3; 15 to 20 mm in diameter) preovulatory follicles as well as from a pool of immature small yellow follicles (SYF; 6 to 8 mm in diameter). The amounts of soluble fibronectin (fibronectin secreted into the incubation medium) and insoluble fibronectin (fibronectin associated with cells plus fibronectin attached to culture substratum) were quantified with a specific ELISA. Fibronectin secreted into the incubation medium (soluble fibronectin) by unstimulated cells increased with advanced stages of follicular maturation. Addition of both cGnRH-I and -II increased the amount of fibronectin secreted into the incubation medium by all follicular cell types. The amount of insoluble fibronectin in culture wells that contained unstimulated cells also increased with advanced stages of follicle development. Both cGnRH-I and -II increased the quantity of insoluble fibronectin by granulosa cells from all follicle types. Total (soluble plus insoluble) fibronectin production was elevated when cGnRH-I or -II was added to F1, F3, and SYF granulosa cells. The magnitude of cGnRH-I or -II stimulation (percentage increase) of soluble, insoluble, or total fibronectin production was calculated as a multiple of the unstimulated (control) value for each follicle type, and they were greatest in cells derived from developing and immature follicles. These results indicate that homologous cGnRH-I and -II are capable of directly modulating the physiology of the avian ovary.