L-arginine, the substrate of nitric oxide synthase, inhibits fertility of male rats

To examine the effect of L-arginine, the substrate of nitric oxide (NO) syn thase, on reproductive function of male rats. Methods: Male rats were gavag ed with either L-arginine (100 or 200 mg.kg(-1).d(-1)), D-arginine (200 mg kg(-1).d(-1)) or vehicle (0.9% NaCl) for seven consecutive days. Their sexu al behaviour and fertility were evaluated using receptive females. Results: L-arginine (200 mg/kg) had no significant effect on sexual competence tin terms of sexual arousal, libido, sexual vigour and sexual performance). In mating experiments, the higher dose of L-arginine effectively and reversibl y inhibited fertility, whilst the lower dose and the inactive stereoisomer D-arginine had no significant effect. The antifertility effect caused by L- arginine was due to a profound elevation in the preimplantation loss mediat ed possibly by impairment in epididymal sperm maturation, hyperactivated sp erm motility and sperm capacitation. Conclusion: Elevated NO production may be detrimental to male fertility.