This study aimed to examine the effect of monocrotaline (MCT)-induced pulmonary hypertension on electrical field stimulation (EFS)-mediated relaxation in rings of rat main pulmonary artery and to see whether treatment with atorvastatin or L-arginine would prevent the action of MCT. Rats were killed 21 days after MCT injection (60 mg/kg), and the main pulmonary arteries were isolated. EFS (40 V, 0.2 milliseconds, 5 seconds, 10 Hz)-induced relaxations in vessels precontracted with phenylephrine (10(-6) to 3 x 10(-6) M) were abolished in MCT-injected group compared with control group. Treatment of MCT group with atorvastatin (10 mg/kg, orally) completely, whereas treatment with L-arginine (500 mg/kg, intraperitoneally) partially but significantly prevented the inhibition. Similarly, acetylcholine (10(-9) to 3 x 10(-5) M)-evoked relaxations that were markedly inhibited in MCT-group were also protected from inhibition after pretreatment with atorvastatin or L-arginine. Responses to endothelium-independent relaxants sodium nitroprusside (10(-9) to 10(-5) M), pinacidil (10(-10) to 10(-4) M), and papaverine (10(-8) to 10(-4) M) were unaltered in MCT-induced pulmonary hypertensive rats. The present findings suggest that MCT-induced pulmonary hypertension inhibits the EFS-mediated relaxation through suppression of endothelial NO production. Reversal of this inhibition by atorvastatin treatment presumably results from stimulation of endothelial nitric oxide synthase expression. Relatively weak protection elicited by L-arginine might be secondary to impaired endothelial nitric oxide synthase activity caused by MCT-induced pulmonary hypertension.