Abnormal renal hemodynamics in salt-sensitive patients with essential hypertension

Thirty hypertensive patients were studied during a low-sodium diet for three days and a high-sodium diet for six days. They were classified as "salt-sensitive" (SS) (n = 10) or "non-salt-sensitive" (NSS) (n = 20) based on the increase in mean blood pressure (BP) with changes in sodium intake from 25 mEq/day to 250 mEq/day (14.7 +/- 1.3% versus 4.0 +/- 0.8%, p less than 0.001). With the high-sodium diet, the SS patients had a greater increase in cardiac output (p less than 0.001), and the increment in mean BP with the salt loading significantly correlated to that in cardiac output (r = 0.672, p less than 0.01). Thus, the increase in BP during short-term salt loading may be attributed to the increase in cardiac output. The role of renal hemodynamics in the increment of BP with salt loading after sodium restriction was evaluated in six SS and 14 NSS patients. Although the glomerular filtration rate was not different in the two groups, the renal vascular resistance was greater (p less than 0.05) in the SS patients than in the NSS ones. Moreover, renal vascular resistance positively correlated to the increment in mean BP with salt loading (r = 0.612, p less than 0.01). Thus, it is suggested that renal vasoconstriction may be an important factor influencing "salt-sensitivity" in essential hypertension, possibly via the impaired renal sodium excretion.