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| |  CHBPR: Long-term Irbesartan, Amlodipine Normalizes Resistance Artery Structure and Endothelial Function By W. A. Thomasson Special to DG News CHICAGO, IL -- September 25, 2001 -- The angiotensin receptor blocker irbesartan and the slow-release calcium channel blocker amlodipine return resistance artery structure toward normal and improve endothelial function in these arteries. These positive results were not observed with the beta-blocker, atenolol, researchers report. This evidence, from two separate studies, was presented yesterday (September 24) at the annual meeting of the Council for High Blood Pressure Research, in Chicago, IL, by Ernesto L. Schiffrin, MD, PhD, and colleagues at Clinical Research Institute of Montreal (Canada) and Sungkyunkwan Univ. in Seoul, South Korea. Previous studies from this and other groups had shown that angiotensin converting enzyme inhibitors likewise returned resistance artery structure and function toward normal. Although the papers noted that these changes might be expected to improve outcomes, neither study examined outcomes or the possibility that medication dosage might be reduced. Resistance arteries are those that are 150 to 350 µm in diameter; these arteries account for most vascular resistance and therefore exert a major influence on blood pressure. The two studies presented yesterday used a pressure myograph to examine resistance arteries obtained by subcutaneous biopsy of the gluteus maximus in patients with mild to moderate essential hypertension. The structural criterion employed was ratio of media thickness to lumen diameter. The functional criterion was the endothelium-mediated vasorelaxation induced by acetylcholine. In the first study, 10 patients who had undergone biopsy before and after one year of treatment with atenolol were switched to irbesartan, with a third biopsy after a further year of treatment. Dr. Schiffrin pointed out that this type of sequential study in the same patients avoids any possible randomization bias. In the second study, 19 patients were randomly assigned to one year of treatment with either atenolol or amlodipine. In both studies, the degree of blood pressure control was virtually the same with both drugs (131/84 with atenolol in the first study and 129/85 in all other groups). The media-lumen ratio decreased from 8.44±0.45 percent to 6.46±0.30 percent (p<0.01) on irbesartan (normotensive mean, 5.9±0.3 percent). On amlodipine, the ratio decreased from 7.89±0.40 percent to 6.81±0.41 percent (p<0.05). Maximal acetylcholine-induced vasorelaxation on irbesartan increased from 81.1±4.1 percent to 94.8±2.0 percent (p<0.01) - essentially indistinguishable from values in normotensive subjects -and on amlodipine increased from 84.3±5.5 percent to 90.5±4.8 percent (p=0.06). Neither media-lumen ratio nor acetylcholine-induced vasorelaxation changed with atenolol treatment, and nitroprusside-induced vasorelaxation, which does not depend on the endothelium, did not change with any treatment.
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