NITRIC-OXIDE SYNTHASE INHIBITORS PREVENT APOMORPHINE-INDUCED AND OXYTOCIN-INDUCED PENILE ERECTION AND YAWNING IN MALE-RATS

The effect of N(G)-nitro-L-arginine methyl ester and N-monomethyl-L-ar ginine, two inhibitors of nitric oxide synthase, on apomorphine- and o xytocin-induced penile erection and yawning, was studied in male rats after intravenous and intracerebroventricular administration. Both com pounds prevented dose-dependently apomorphine and oxytocin responses, when given sistemically (5-50 mg/kg) or centrally (30-500 mug per rat) , but N(G)-nitro-L-arginine methyl ester was about 5 times more potent than N(G)-monomethyl-L-arginine. The D-isomer of N-mono-methyl-L-argi nine, which does not inhibit nitric oxide synthase, was ineffective. T he results suggest that central nitric oxide is involved in the expres sion of penile erection and yawning induced by apomorphine and oxytoci n.