Heme oxygenase-mediated endothelial dysfunction in DOCA-salt, but not in spontaneously hypertensive, rat arterioles

Vascular heme oxygenase (HO) metabolizes heme to form carbon monoxide. Carbon monoxide inhibits nitric oxide synthase and promotes endothelium-dependent vasoconstriction. We reported HO-1-mediated endothelial dysfunction in Dahl salt-sensitive hypertension. Previous studies suggested that salt-sensitive hypertensive rats, but not spontaneously hypertensive rats (SHR), display endothelial dysfunction. This study examines the hypothesis that HO-1-mediated arteriolar endothelial dysfunction develops in deoxycorticosterone acetate (DOCA)-salt hypertensive (DOCA) rats, but not in SHR. Uninephrectomized (isoflurane anesthesia) male Sprague-Dawley rats received DOCA injections and saline drinking solution for 4 wk. Rats subjected to sham surgery received vehicle injections and tap water. Blood pressure was elevated in DOCA rats and SHR compared with sham and Wistar-Kyoto (WKY) groups. Aortic HO-1 expression and blood carboxyhemoglobin levels were elevated in the DOCA group, but not in SHR. In isolated gracilis muscle arterioles, ACh caused concentration-related vasodilation in all groups, with attenuated maximum responses in DOCA, but not in SHR, arterioles. Acute pretreatment with an inhibitor of HO, chromium mesoporphyrin, restored ACh-induced responses in DOCA arterioles to sham levels. ACh responses remained the same in SHR and WKY arterioles after chromium mesoporphyrin treatment. These data show that HO-1 levels and activity are increased and arteriolar responses to ACh are decreased in DOCA rats, but not in SHR. Furthermore, in DOCA arterioles, an inhibitor of HO restores ACh-induced vasodilation to sham levels. These results suggest that elevated HO-1 levels and activity, not resulting from hypertension per se, contribute to endothelial dysfunction in DOCA rats.