This study was designed to determine whether recombinant human erythropoietin (rHuEpo) administration increases vascular nitric oxide (NO) production in healthy rats. We hypothesized that rHuEpo hypertension is associated with increased endothelial expression of nitric oxide synthase and augmented NO-dependent vasodilation. Male rats were instrumented with pulsed Doppler flow probes around their ascending aorta and with arterial and femoral catheters. Rats were treated for 14 days with rHuEpo (2 U/d) or vehicle. rHuEpo elevated hematocrit and increased mean arterial pressure (142 +/- 3 versus 116 +/- 4 mm Hg). Thoracic aorta segments from rHuEpo rats had a modest increase in NO-dependent relaxation assessed by acetylcholine (10(-10) to 10(-5) mol/L) relaxation of phenylephrine (PE) (10(-6) mol/L) contracted arteries. Relaxation to NO-donor, s-nitrosyl acetylpenicillamine, and PE contraction were not different from control arteries. The NO synthase inhibitor, N-omega-nitro-L-arginine, increased blood pressure and total peripheral resistance more in rHuEpo rats at both 10 and 30 mg/kg. NOS expression in rHuEpo aorta and plasma NOx concentrations were increased compared with control. Thus, it appears that vascular eNOS expression is increased and causes basal vasodilation in rHuEpo hypertensive rats.