Renin and blood volume in chronic renal failure: a comparison with essential hypertension

Sixty-five patients with advanced chronic renal failure (CRF) but a normal extracellular fluid volume (ECFV), including 31 dialysis patients, were studied. Plasma volume, blood volume (BV), plasma renin activity (PRA), and mean arterial pressure were measured to examine whether hypertension (when present) is renin dependent, or whether it is related to an abnormal distribution of ECFV between the intra- and extravascular spaces. PRA was higher in dialysis than nondialysis patients, but the incidence of hypertension was the same. In both groups hypertensive patients with normal PRA and normotensive patients with elevated PRA were present. The patients were compared to 65 patients with essential hypertension (EH) and 56 normals. The BV and BV-to-interstitial fluid volume ratio were similar in these groups. We found no decreased BV in patients with EH as has previously been reported by others, possibly because we used an appropriate normalization index and matched control groups. In sum, hypertension in CRF patients with a normal ECFV cannot always be explained by elevated renin levels. In this respect, CRF patients resemble patients with EH. An abnormal extracellular fluid distribution does not seem to be involved in the maintenance of hypertension.