Effect of estradiol on Ca2+ release from intracellular stores in porcine oocytes stimulated by prolactin, theophylline, or guanosine triphosphate

The interaction between prolactin and theophylline as well as between prolactin and guanosine triphosphate during Ca2+ release from intracellular stores of estradiol-treated porcine oocytes isolated from the ovary at the stage of follicular growth were studied using fluorescent Ca2+-sensitive probe chlortetracycline. In the absence of estradiol, prolactin or theophylline induced Ca2+ release from intracellular stores; however, no increase in Ca2+ release was observed after their combined action. Conversely, Ca2+ release from intracellular stores increased only after the combined exposure to prolactin and theophylline in the presence of estradiol. In the absence of estradiol, guanosine triphosphate induced calcium release alone and together with prolactin. Protein kinase C regulated Ca2+ release from intracellular stores after the combined exposure to prolactin and theophylline only in the presence of estradiol; while the activation of protein kinase C required no estradiol during the combined exposure to prolactin and guanosine triphosphate. The data obtained indicate the effect of estradiol on Ca2+ release from intracellular stores after the combined exposure to prolactin and theophylline, while no such effect was observed after the combined exposure to prolactin and guanosine triphosphate.