Potassium intake during cell dehydration.

Isotonic NaCl is ingested in addition to water by cell-dehydrated rats in two-bottle tests. The objective of the present work was to find out whether mineral intake in the cell-dehydrated rat is specific to NaCl in a five-bottle test. Adult male Sprague Dawley rats had distilled water and four mineral solutions at palatable concentrations (0.01 M KCl, 0.05 mM CaCl2, 0.15 M NaHCO3, 0.15 M NaCl) simultaneously available for consumption. Cell-dehydration was produced infusing 1.5 ml of NaCl solution (0.15, 0.25, 0.5, 1.0, 2.0, 4.0 M) intravenously for 10 min and intakes were recorded for the next hour. It was observed a NaCl concentration-dependent increase in 0.01 M KCl intake. The ingestion of the other mineral solutions was not significantly altered compared to infusion of 0.15 M NaCl. The ingestion of KCl was not related to changes in serum potassium concentration. The ingestion of KCl was reduced in half and water was the preferred fluid when the five-bottle test was performed with mineral solutions at isomolar (0.15 M) concentrations. There was no increase in intake of other mineral solution in the isomolar test. No preference was observed for palatable or isomolar solutions during early extracellular dehydration until 4 h after subcutaneous injection of furosemide, in spite of the increase in total volume intake. Therefore, mineral intake induced by cell dehydration is not specific for NaCl solution. The type of mineral solution available influences the choice and KCl is the preferred solution of the cell-dehydrated rat in the conditions of the present study.

Effect of volume expansion on tubular reabsorption of protein by normal and nephrotic rats.

1. Normal (N) and nephrotic (NS) rats were infused with hyperoncotic human serum albumin or isotonic saline to alter plasma albumin concentration. The renal handling of albumin was evaluated by measuring the albumin/inulin clearance ratio (CA/CIN). The dextran/inulin clearance ratio, CD/CIN, was determined using dextran of 16,000 (14C) and 70,000 (3H) molecular weight. Five groups of rats were studied: NaA, NaS, NSaA, NdS and NSdS. The subscripts A and S indicate albumin and saline infusion; the superscripts a and d denote the measurement of CA/CIN and CD/CIN. 2. When vascular volume was expanded by infusion of albumin or saline, diuresis was increased in all groups (P less than 0.05). Inulin clearance was increased (P less than 0.05) in all groups except NaS, for which it was unchanged. The CA/CIN ratio was increased (P less than 0.05) for the three groups measured, NaA, NaS, and NSaA and the increase was independent of changes in plasma albumin concentration. In contrast, C16D/CIN decreased for NdS and NSdS and C70D/CIN decreased for NSdS but was unchanged for the NdS group. 3. The increase of CA/CIN could not be correlated with high albumin load, since it was also observed when plasma albumin was lowered by saline infusion. CD/CIN did not increase with saline infusion. Therefore an increase in glomerular permeability due to the volume expansion could not explain the increase in CA/CIN during albumin infusion. 4. We conclude that the depression of albumin reabsorption was a consequence of volume expansion. A model is presented which accounts for the effect of increased tubular flow on albumin reabsorption.