We have demonstrated previously that inhibition of angiotensin-converting enzyme (ACE) with enalapril and angiotensin II blockade with losartan improve acetylcholine-dependent endothelial function in resistance vessels of patients with Type II diabetes. It was therefore of interest to examine the effect of losartan on conduit vessel function in this group. The influence of losartan (50 mg daily for 4 weeks) on endothelium-dependent and -independent vasodilator function was determined in 12 subjects with Type II diabetes using a randomized, double-blind, placebo-controlled crossover protocol. Conduit vessel endothelial function was assessed using high-resolution ultrasound and the brachial artery response to reactive hyperaemia (flow-mediated dilation; FMD); glyceryl trinitrate (GTN) was used as a non-endothelium-dependent dilator. Losartan administration significantly increased the FMD response from 5.2±0.7% (mean±S.E.M.) to 7.4±0.6% of vessel diameter (P < 0.05; paired t-test). There was no effect of losartan on the endothelium-independent responses to GTN (17.8±1.8% to 17.6±1.2%). Consistent with our previous findings in resistance vessels, administration of 50 mg of losartan daily improves NO-mediated dilation in the conduit vessels of subjects with Type II diabetes. Together with the findings that both ACE inhibition and angiotensin II blockade improve resistance vessel function in this group, it is likely that at least some of the beneficial effect is mediated through the angiotensin II/type 1 receptor pathway. A type 1 receptor antagonist seems a reasonable alternative to an ACE inhibitor to maintain conduit vessel endothelial function in Type II diabetic subjects.
The Heterogeneous Nature of Conduit Vessel Endothelial Function: A Study in the Brachial and Carotid Vasculature