['Patients with HIV have an increased incidence of pulmonary artery hypertension. This study was designed to determine if the naturally occurring antioxidant dihydroxybenzyl alcohol (DHBA) could counteract the deleterious effects of ritonavir (RTV), an HIV-protease inhibitor known to impair endothelial function and increase oxidative stress.', 'Antioxidant assays were performed on DHBA in a cell free system. Glutathione (GSH) levels were measured in human pulmonary artery endothelial cells (HPAEC) to determine the effect of DHBA on the level of oxidative stress in cells treated with RTV. Myograph analysis was performed on porcine pulmonary artery (PA) rings after treatment with RTV and/or DHBA. Likewise, reactive oxygen species (ROS) production was assessed in porcine PA rings after RTV +/- DHBA using a lucigenin reaction. Immunohistochemical staining for endothelial nitric oxide synthase (eNOS) was also performed in porcine PAs treated as above.', 'DHBA demonstrated significant antioxidant activity in a cell free system that surpassed that of vitamin C. Also, treatment with DHBA reduced RTV-induced reduction in endothelium-dependent vasorelaxation and eNOS staining and increased superoxide anion levels. Meanwhile, there was a reversal in RTV-induced oxidative stress leading to reduced GSH levels in HPAECs after treatment with DHBA.'] Does natural antioxidant dihydroxybenzyl alcohol block ritonavir-induced endothelial dysfunction in porcine pulmonary arteries and human endothelial cells?