Abstract: AIM: To investigate the role of nitric ox-ide (NO)in development ofPulmonary artery hyperten-sion and the effects of NO on the release of endothelin-1(ET-1)in rats withPulmonary hypertension and with chronic hypoxia and hypercapnia.METHODS: Twenty-nine rats were divided into four groups:the control group;the hypoxia-hypercapnia grouP;the hypoxia-hy-percapnia grouP+L-Arg grouP(l-Arg),intraperitoneal injection ofl-Arg (500 mg·kg^-1)every day for 1 month and the hypoxia-hypercapnia grouP+L-Arg +L-NAME grouP(l-NAME),intraperitoneal injection ofl-Arg(500 mg·kg^-1)andl-NAME (5 mg·kg^-1)every day for 1 month.All these rats except those in the control grouPwere exposed to hypoxia-hypercapnia 10 hours each day for 1 month.MeanPulmonary arteryPressure(mPAP)and ET-1 inPlasma were detected in these rats.And the relationshiPbetween mPAPand ET-1 was ana-lyzed.RESULTS: The values of mPAPin the hypoxia-hypercapnia grouPandl-NAME groups were higher than those in the control grouP(P<0.001)andl-Arg (P<0.05,or 0.01)groups;the value of mPAPin thel-Arg grouPwas higher than that in the control grouP(P<0.05).There was no difference in ET-1 between the hy-poxia-hypercapnia grouPand thel-NAME grouP(P>0.05),and the same between thel-Arg grouPand the control grouP(P>0.05).But thelevels of ET-1 were higher in the hypoxia-hypercapnia grouPandl-NAME groups than those in the control grouP(P<0.001)andl-Arg groups (P<0.05,or 0.01).There wasPositive correlation between mPAPand ET-1 (r =0.768,P<0.05).CONCLUSION: NO can inhibit the release of ET-1,and downregulate thePressure ofPulmonary artery in ratswith chronic hypoxica and hypercapnica.

Key words: pharmacology, nitric oxide, endothelin-1, L-arginine, hypoxia, hypercapnica