Role of nicotinamide adenine dinucleotide in ethanol-induced depressions in testicular steroidogenesis

It is rapidly becoming accepted, without direct evidence, that a change in the NAD⁺/NADH ratio in the testes produced by the metabolism of ethanol is the principal mechanism involved in its now well-established effects on testicular steroidogenesis. The purposes of the present studies were 2-fold: (1) to examine whether, in fact, in vivo or in vitro ethanol exposure alters the NAD⁺/NADH ratio in the testes; and (2) to examine the validity of previous reports in which it was found that NAD⁺ prevented the effects of ethanol on testicular steoidogenesis under in vitro conditions. With regard to the first objective, we found that a large dose of ethanol (2.5 g/kg) markedly reduced gonadotropin-stimulated testicular steroidogenesis in vivo in the male rat, but it did not alter the NAD⁺ and NADH concentrations in the testes. Similarly, extremely high ethanol concentrations (200 mM) substantially suppressed hMG-stimulated testosterone biosynthesis in in vitro Leydig cell preparations, but no change in NAD⁺ concentration occurred; NADH levels were very low in the Leydig cell preparations (less than 2% of NAD⁺ levels), but did not appear to change as a function of ethanol exposure. Finally, in contrast to previously published results, we found that NAD⁺ (1 mM) did not prevent the in vitro effects of ethanol on cAMP-stimulated testicular steroidogenesis. Consequently, our results fail to support the hypothesis that acute in vivo or in vitro ethanol administration inhibits the biosynthesis of testosterone by altering the NAD⁺/NADH ratio in the testes.