Reduction in libido and fertility of male rats by administration of the nitric oxide (NO) synthase inhibitor N-nitro-L-arginine methyl ester

The role of nitric oxide (NO) in libido and fertility of male rats was inve stigated by administration of the NO synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) (25 or 50 mg/kg/day). L-NAME caused marked reduction of precoital sexual behaviour, and a failure of most rats to mount or ejacu late during the test interval. In most matings that were successful, recove red spermatozoa were present in normal numbers. In mating experiments, L-NA ME profoundly reduced the fertility of male rats. In those animals that did succeed in mating, the quantal pregnancy and the number of implants were r educed. After cessation of treatment with L-NAME, the fertility parameters returned close to normal. The inactive stereoisomer, D-NAME, caused none of the above effects when administered to rats. The results suggest that NO i s essential for the expression of normal libido and fertility in male rats. It is likely that NO is required both in the male reproductive tract and i n the brain.