Mechanism of impaired urinary concentration in chronic primary glomerulonephritis

Mechanism of impaired urinary concentration in chronic primary glomerulonephritis. To define the role of medullary damage and the influence of solute load and blood pressure (BP) in impairing urinary concentration, patients with chronic glomerulonephritis were investigated by histological and functional studies. In 59 biopsy specimens, the degree of medullary fibrosis was correlated inversely with urinary specific gravity and was significantly greater in hypertensive than in normotensive subjects. The following clearance studies were carried out in patients with a GFR of 15 to 40ml/min in maximal antidiuresis: (1) Eight patients were studied while receiving a high sodium and protein diet and then after 1 week of low sodium, low protein diet; (2) ten patients were loaded with hypertonic saline (3%) to increase urine volume up to 25 to 30% of GFR; (3) the concentrating ability was compared in 15 normotensives and 15 hypertensives with comparable GFR; (4) the concentrating ability was studied in nine hypertensive patients before and after drug-induced normalization of BP. In (1) no change occurred in maximal urine osmolality (UOsm) even if fractional sodium excretion and filtered load of urea were reduced. In (2), values of UOsm fell below those of plasma osmolality. In (3), UOsm and negative free-water generation were lower in hypertensive than in normotensive subjects. In (4), normalization of BP was not associated with any change in UOsm These results indicate that osmotic diuresis does not play a critical role in reducing urinary concentration. This defect is better accounted for by an intrinsic medullary damage, enhanced in hypertensive patients, which may impair the permeability of collecting ducts to water. Mécanisme de l'altération de la concentration urinaire au cours des glomérulonéphrites chroniques primitives. Afin de définir le rôle des altérations médullaires et de l'influence de la charge en solutés et de la pression sanguine (BP) dans le défaut de concentration urinaire, des malades atteints de glomérulonéphrite chronique ont été explorés par des études histologiques et fonctionnelles. Dans 59 biopsies, le degré de fibrose médullaire était inversement corrélé à la densité spécifique urinaire, et était significativement plus important chez les hypertendus que chez les normaux tendus. Les études de clearance suivantes ont été entreprises chez des malades dont GFR était de 15–40ml/min en antidiurèse maximale: (1) huit malades ont été étudiés alor