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-arginine, two inhibitors of nitric oxide synthase, on apomorphine- and oxytocin-induced penile erection and yawning, was studied in male rats after intravenous and intracerebroventricular administration. Both compounds 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-arginine, which does not inhibit nitric oxide synthase, was ineffective. The results suggest that central nitric oxide is involved in the expression of penile erection and yawning induced by apomorphine and oxytocin.