Protein expression, vascular reactivity and soluble guanylate cyclase activity in mice lacking the endothelial cell nitric oxide synthase: contributions of NOS isoforms to blood pressure and heart rate control

Objective: Both disruption of the endothelial nitric oxide synthase (eNOS) gene and pharmacological inhibition of the NOS produce modest hypertension. It is unclear if and to what extent NOS isoforms other than eNOS contribut e to this effect and how loss of one copy of the eNOS gene might impact on vascular reactivity or eNOS protein expression. Methods: We examined protei n expression, vascular reactivity, activity of soluble guanylate cyclase, b lood pressure and heart rate in mice completely lacking the eNOS gene (eNOS (-/-)), wild-type mice (eNOS(+/+)) and mice heterozygotic for the eNOS gene (eNOS(+/-)). Results: While eNOS(-/-) mice had mild hypertension and brady cardia, eNOS(+/-) mice were normotensive. In control mice, oral administrat ion of L-NAME (approximately 100 mg/kg/day x21 days) increased blood pressu re to levels observed in eNOS(-/-) mice. In eNOS(-/-) mice, chronic oral ad ministration of L-NAME had no effect on blood pressure, suggesting that inh ibition of other NOS isoforms unlikely contribute to hypertension. L-NAME t reatment induced bradycardia in both control and eNOS(-/-) mice, suggesting that both eNOS and other isoforms of NOS might be involved in heart rate c ontrol. Studies of aortic rings from eNOS(-/-) mice revealed a complete lac k of endothelium-dependent vascular relaxation in response to acetylcholine and the calcium ionophore A23187 and an increase in sensitivity to phenyle phrine, serotonin and nitroglycerin. Aortic rings from eNOS(+/-) mice demon strated only minor alterations of responses to nitroglycerin and a normal r elaxation to either acetylcholine or A23187 compared to vessels from eNOS(/+). Western analysis demonstrated that eNOS expression was virtually ident ical between eNOS(+/+) and eNOS(+/-) mice and was absent in eNOS(-/-) mice. The activity of lung-isolated soluble guanylate cyclase was identical in t he three strains of mice. Conclusions: We conclude that loss of one copy of the eNOS gene, as observed in heterozygotic animals, has no effect on vasc ular reactivity, blood pressure or eNOS protein expression. Isoforms of NOS , other than eNOS are unlikely involved in blood pressure regulation but ma y participate in heart rate control. (C) 1999 Elsevier Science BN. All righ ts reserved.