Enhanced gastrointestinal absorption of aluminium in uraemia: time course and effect of vitamin D.

The present study examines the time course of aluminium absorption in uraemic rats vs controls and investigates the effect of vitamin D. Following an oral load of 410 mumol aluminium there was a significant increase in the urinary excretion rate of aluminium as early as 60 min in uraemic rats. Compared with controls this increase was significantly greater in uraemic animals and maximum excretion rates (77 +/- 49 vs pre-load 2 +/- 1 nmol Al/h) were achieved after 2 h. When vitamin-D-deficient rats with normal renal function were compared with vitamin-D-replete controls, the latter excreted a significantly greater amount of the oral dose of aluminium in their urine (727 +/- 361 vs 359 +/- 140 nmol Al/5d; P less than 0.02) and the post-load increase in the serum aluminium concentration was more pronounced in the vitamin-D-replete animals. Aluminium administered i.v. resulted in similar urinary aluminium excretion rates in both groups. In uraemic rats, however, regardless of their vitamin D status, administration of 1,25(OH)2D3 had no effect on the amount of urinary aluminium excretion after oral or i.v. loads. These findings suggest that although in rats with normal renal function aluminium absorption appears to be partly vitamin D dependent, 1,25(OH)2D3 does not further augment the enhanced gastrointestinal absorption of aluminium in uraemia.