Greater loop chloride uptake contributes to blunted pressure natriuresis in Dahl salt sensitive rats.

A blunted pressure natriuretic response is present in Dahl salt sensitive rats. To determine whether this results from tubular or glomerular mechanisms, late proximal, early distal, and late distal micropuncture were performed in salt resistant (R), salt sensitive (S), or salt sensitive rats with renal perfusion reduced to that of R rats (S-AC). Differences in neuro-endocrine background between groups were eliminated by renal denervation and by fixing plasma aldosterone, norepinephrine, and vasopressin levels by infusion. Renal perfusion pressure was greater (P less than 0.05) and inulin clearance less (P less than 0.05) in S than R rats. Urinary sodium excretion, however, was not different. S-AC had renal perfusion pressures that were similar to R rats and inulin clearance similar to S rats. Urinary NaCl excretion was less (P less than 0.05) than either group. Single nephron inulin clearance, fluid, and chloride delivery to late proximal sites were not different between groups. Absolute and fractional chloride delivery to early distal sites was less (P less than 0.05) in S-AC than R or S but not different between R and S. Late distal chloride delivery was not different between any group. Calculated loop chloride reabsorption was greater in S-AC than R or S. Thus, the lower urinary NaCl excretion in S-AC rats is in part due to increased loop chloride reabsorption. This effect is probably intrinsic to the S kidney as it occurs despite renal denervation when plasma levels of vasopressin, norepinephrine, and aldosterone are fixed. The increased loop chloride uptake is abolished when perfusion pressure increases.