Ovarian lipoxygenase activity and its regulation by gonadotropin in the rat

In our previous study a dose-dependent blockage of follicular rupture at ovulation by inhibitors of lipoxygenase was demonstrated. Here the presence of 5-lipoxygenase activity in the whole ovary and in the Graafian follicle is estimated by a chemiluminescence assay using unlabeled arachidonic acid as substrate in the presence of luminol and by conversion of 14C-arachidonic acid into lipoxygenase products as separated by HPLC. Both approaches demonstrated lipoxygenase activity in whole ovarian homogenates and in homogenates of preovulatory Graafian follicles. Furthermore, within 6 h after stimulation in vivo with hCG, lipoxygenase activity was increased by 2-fold in the whole ovarian homogenate and by 5-fold in the follicular homogenate. These results confirm the presence of lipoxygenase in rat ovaries, and its stimulation by gonadotropin and thus corroborate the suggested involvement of lipoxygenase products in follicular rupture at ovulation.