Involvement of catecholamines in the regulation of oocyte maturation in frogs

Abstract

The present study investigates the role of catecholamines in the regulation of Bufo arenarum oocyte maturation. The metabolic changes in the oxidation of carbohydrates and the meiotic resumption evinced by the germinal vesicle breakdown were used as indicators of cytoplasmic and nuclear maturation, respectively. The results obtained suggest that noradrenaline (norepinephrine) could be one of the factors responsible for the metabolic behaviour that characterises cytoplasmically immature oocytes. The use of adrenaline (epinephrine), on the other hand, induced a metabolic change which made oocytes cytoplasmically mature. The effect of both catecholamines, which was dose-dependent, was observed in ovarian oocytes (surrounded by follicle cells) as well as in coelomic oocytes (free from follicle cells), suggesting the presence of adrenergic receptors in the gamete. The results obtained using adrenergic agonists and antagonists suggest that the effect of adrenaline would be due to an interaction with β₂-receptors. Although catecholamines have an influence on the determination of the stage of cytoplasmic maturation of the oocytes, they do not affect nuclear maturation by themselves. Nevertheless, pretreatment of follicles with adrenaline caused a significant inhibition in progesterone-induced nuclear maturation even though this effect was markedly weaker when using noradrenaline.