Previous studies in our laboratory have demonstrated that alpha-methyldopa, a potent inhibitor of catecholamine synthesis, reduced both libido and erectile function in sexually mature male rats as it does in humans. In this report, those studies were extended to identify the drug's effect upon catecholamine content in the brain, spinal cord and penile erectile tissue in mature male rats. Because many men report that the adverse effects of alpha-methyldopa upon their sexual performance continue after withdrawal from the drug, a 2nd group of animals was retested after the drug was stopped. Results of the group I study showed diminished copulatory and erectile activity as well as penile and brain norepinephrine content. In the group II rats there was a continued significant reduction in erectile and copulatory activity. At the same time, brain, spinal cord and penile tissue content of norepinephrine returned to normal levels. In another experiment an alpha2-receptor antagonist was administered with alpha-methyldopa and no inhibition of the effects of alpha-methyldopa was observed. These findings imply that the effect of alpha-methyldopa on sexual function is mediated in the central nervous system as an abnormality of receptor function.
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