Nicotinamide inhibition of Xenopus laevis oocyte maturation

Nicotinamide at a concentration of 20 mM prevented progesterone-induced germinal vesicle breakdown (GVBD) of Xenopus laevis oocytes in vitro in a reversible manner, whereas nicotinic acid did not. The vitamin was inhibitory even when applied 30 min after the addition of progesterone and blocked the induction of GVBD by microinjected maturation-promoting factor (MPF). Nicotinamide also prevented the burst of protein phos-phorylation associated with MPF expression and increased the oocyte cAMP level, whereas intracellular NAD content and protein synthesis were not affected. The present results suggest that nicotinamide acts by increasing the intracellular level of cAMP and by blocking MPF action.