Abstract-Structural alterations of small arteries in patients with essential hypertension are characterized by inward eutrophic remodeling. However, small arteries in patients with secondary hypertension, as well as in experimental models of hypertension with high circulating renin, are characterized by inward hypertrophic remodeling, which is characterized by smooth muscle cell hypertrophy in animal models. The aim of our study was to determine whether remodeling of subcutaneous small arteries in patients with secondary forms of hypertension is associated with smooth muscle cell hypertrophy and/or alterations in the elastic modulus of the vessel wall. Fifteen patients with renovascular hypertension, 9 with primary aldosteronism, and 13 with essential hypertension and 9 normotensive subjects were included in the study. A biopsy of subcutaneous fat was taken from all subjects. Small arteries were dissected, and morphology was determined on a micromyograph. Unbiased estimates of cell volume and number were made in fixed material. From the resting tension-internal circumference relation of the small arteries, the incremental elastic modulus was calculated and plotted as a function of wall stress. Blood pressure was greater in patients with essential hypertension, renovascular hypertension, or primary aldosteronism than in normotensive subjects, but no significant difference was observed among the 3 groups of hypertensive patients. The media/lumen ratio, the medial cross-sectional area, and the smooth muscle cell volume were significantly greater in patients with renovascular hypertension than in normotensive subjects and patients with essential hypertension. No difference in cell number or in the elastic properties was observed among the 4 groups of subjects. In conclusion, our data demonstrate for the first time that a pronounced activation of the renin-angiotensin-aldosterone system is associated with vascular smooth muscle cell hypertrophy in human hypertension in a manner similar to that found in animal models. Key Words: hypertension, secondary Ⅲ hypertrophy Ⅲ remodeling Ⅲ renin-angiotensin-aldosterone system Ⅲ vascular resistance I t is well established that structural changes of small arteries are associated with hypertension. 1-3 These alterations include a decreased luminal diameter and an increased medial thickness, 3-6 thus leading to an increased media/lumen ratio. The media/lumen ratio in small arteries may be increased as a consequence of eutrophic remodeling (ie, a rearrangement of otherwise normal material around a narrowed lumen) or of hypertrophic remodeling (hypertrophy or hyperplasia of vascular smooth muscle cells). 7,8 Present evidence indicates that in animal models of genetic hypertension and in patients with essential hypertension, vascular structural abnormalities of small arteries are, in general, characterized by an inward eutrophic remodeling, 7,8 as evaluated by the calculation of remodeling and growth indices. 7,9 Similar conclusions have been drawn when structural abnormalities were ...