Renal concentrating defect in protein malnutrition: the role of the thick ascending limb of Henle and inner medullary collecting duct.

The present study was carried out to examine the effect of chronic dietary protein restriction on renal water handling in the rat. During hypotonic saline infusion, the malnourished rats showed a lower free-water clearance, corrected by inulin clearance (7.2 +/- 0.4%), than normal rats (13.6 +/- 2.5%, p less than 0.051), although the fractional distal delivery of sodium did not differ from normal. Throughout hypertonic saline diuresis the free-water reabsorption (TcCH20) corrected by inulin clearance was lower in malnourished rats (6.62 +/- 0.64%) than in control animals (9.25 +/- 0.62, p less than 0.05). Moreover, when TcH20 was referred to the osmolar clearance, malnourished animals showed lower values than normal. These results suggest a defect in NaCl transport in the thick ascending limb of Henle. In vitro measurements of diffusional water permeability (PDW) in the inner medullary collecting duct (IMCD) obtained from malnourished rats showed an increase from 40.0 +/- 5.4 x 10(5) cm/s to 71.3 +/- 5.4 x 10(5) cm/s by adding maximum effective concentration (50 microU/ml) of arginine vasopressin (VP) to the bath. These values were not different from the PDW observed in the IMCD of normal rats. In another series of microperfusion experiments, the hydraulic conductivity in IMCD of malnourished rats measured also in the presence of maximum effective concentration of VP was 29.7 +/- 3.4 x 10(-6) cm/atm/s, a mean value not significantly different from that observed in the IMCD of normal rats (35.2 +/- 4.3 x 10(-6) cm/atm/s).(ABSTRACT TRUNCATED AT 250 WORDS)