BackgroundTreatment of essential hypertensive patients with an AT1angiotensin receptor antagonist has previously resulted in correction of resistance artery structure and endothelial function, whereas in a parallel group treated with the beta-blocker atenolol there was no improvement of altered vascular structure and function. To test the hypothesis that patients previously treated with atenolol could present improvement of vascular structure and endothelial function if they were subjected to blockade of the renin–angiotensin system, we crossed over hypertensive patients that had been randomized to treatment with the beta-blocker atenolol to treatment with the AT1antagonist irbesartan, and studied small artery structure and endothelial function before and after treatment.MethodsEleven essential hypertensive patients (51±2 years, range 38–65; 75% male) that had previously been randomized to treatment with atenolol and treated for 1 year with good blood pressure control, were crossed over to treatment with the AT1antagonist irbesartan for 1 year. Small resistance arteries were dissected from gluteal subcutaneous biopsies that were performed before and after 1 year of treatment. The structure and endothelial function of the resistance arteries were studied on a pressurized myograph.ResultsBlood pressure control (129±3.3/85±1.8 mmHg) was identical to that achieved previously with atenolol (131±3.3/84±1.1 mmHg). Following 1 year of treatment, the arterial media width to lumen ratio (M/L) of resistance arteries (lumen diameter, 150–350 μm), which had remained unchanged under atenolol treatment, decreased from 8.44±0.45% when patients were on atenolol, to 6.46±0.30%,P<0.01, when patients received irbesartan. Maximal acetylcholine-induced endothelium-dependent relaxation was 81.1±4.1% when patients were on atenolol, unchanged from before starting treatment with the beta-blocker, and was normalized by irbesartan (to 94.8±2.0%,P<0.01).ConclusionCrossing over essential hypertensive patients with well-controlled blood pressure from the beta-blocker atenolol to the AT1receptor antagonist irbesartan resulted in correction of previously persistently altered vascular structure and endothelial function, suggesting a structural and endothelial vascular protective effect of antihypertensive treatment with the AT1receptor antagonist.