Renal handling of aluminum in the rat: clearance and micropuncture studies.

Previous uncertainty regarding glomerular ultrafilterability (UF) of aluminum has limited the definition of renal Al handling. Glomerular micropuncture was therefore performed in hydropenic Munich-Wistar rats infused with AlCl3 to achieve plasma (P) Al levels between 2 and 10 mg/liter. Glomerular fluid, P, and urine Al concentrations were measured by flameless atomic-absorption spectrophotometry. UFA1 was inversely correlated with PA1 [%UFA1 = 10.3 - 8.4 (log PA1), r = -0.90, P less than 0.01]. When this equation was used to calculate the filtered load (FLA1), A1 excretion (UA1V, ng/min) in simultaneously collected samples was found to be a direct function of FLA1 [UA1V = 5.7 + 0.37 (FLA1), r = 0.93, P less than 0.01]. Fractional excretion (FE) of A1 was 39.4 +/- 4.2% in these hydropenic experiments (FENa = 0.3 +/- 0.1%). We next evaluated the tubular handling of A1 (using these UF data) during step-wise extracellular fluid volume expansion with isotonic saline (2.5, 5.0, 7.0, and 7.0% body wt) and during the infusion of increasing doses (2.7, 5.3, 8.0, and 8.0 mg X kg-1 X h-1) of furosemide as urinary losses were quantitatively replaced. The natriuresis produced by volume expansion (FENa = 1.0, 3.0, 8.4, and 7.9%) and furosemide (FENa = 4.2, 6.0, 6.6, and 6.7%) were comparable. At similar FLA1, 7% volume expansion but not furosemide (at any dose) increased UA1V (240 and 95 ng/min, respectively, vs. 116 ng/min in hydropenia) and FEA1 (84.5 and 29.4 vs. 37.4%, respectively). These data indicate that at pharmacological PA1 levels, less than 8.4% of PA1 is ultrafilterable, suggesting extensive plasma protein binding.(ABSTRACT TRUNCATED AT 250 WORDS)