Age-Related Alterations in the Mechanism of Renovascular Contractility in Patients with Essential Hypertension.

Systemic hemodynamics and renal blood flow (RBF) were studied before and during isometric exercise (IE) in 48 hypertensive patients. Of the 48 hypertensives, 21 were unmedicated and the remaining 27 patients were given one of the following drugs for 3 days prior to the study: 15 patients were treated with Enalapril (5 mg/day) and 12 patients were treated with Bunazosin (2 mg/day). Cardiac output (CO) and RBF were measured simultaneously with two different thermodilutional catheters. To elucidate the influence of aging on the renovascular response to IE, each group was divided into younger (age > 50) and older (age > or = 50) subgroups. RBF decreased and calculated renovascular resistance (RVR) increased significantly during IE in the unmedicated group, but showed no difference in the degree of changes in these parameters between the younger and older subgroups. In the Bunazosin group, RBF and RVR did not change during exercise in either subgroups. In the Enalapril group, RBF did not change in either subgroup, and RVR increased significantly in the younger subgroup, but was unchanged in the older subgroup. There was a negative linear relationship between delta RVRI (change of RVR corrected by body surface area) and age (y = -0.15x + 9.7, r = -0.59: p < 0.05). Plasma norepinephrine increased after IE, but these changes were not significant in all 3 groups. These data suggest that the enhanced renovascular contractility during IE is accomplished mainly through alpha 1-adrenoceptor, and the responsiveness of alpha 1-adrenoceptor may decrease with age.(ABSTRACT TRUNCATED AT 250 WORDS)