Renal filtration, reabsorption and excretion of aluminium in the rat

Abstract

1. Plasma and urinary aluminium levels, and renal function, were investigated in a control group of rats (n = 5) and in two groups that received an intravenous bolus dose of aluminium chloride (either 25 micrograms or 800 micrograms of aluminium, n = 7 and 5, respectively). 2. In the control group (plasma aluminium concentration 76.8 +/- 14.2 ng/ml), 59.4 +/- 3.5% of the plasma aluminium was ultrafilterable. The percentage ultrafilterable after the administration of 25 micrograms of aluminium was 41.9 +/- 7.8 (plasma concentration 154.3 +/- 18.6 ng/ml). However, after administration of 800 micrograms of aluminium, to give a plasma concentration of 19,800 +/- 2956 ng/ml, only 1.06 +/- 0.13% was ultrafilterable. 3. Such results have generally been interpreted as indicating an increase in protein-binding of aluminium with increasing aluminium concentration. In buffered aqueous solutions of aluminium chloride at pH 7.4, with an aluminium concentration of 189 +/- 6 ng/ml, 96.12 +/- 0.02% was ultrafilterable (n = 6). This concentration is comparable with that attained in the low-dose (25 micrograms) aluminium group of animals and suggests that the difference between the ultrafilterable percentage of aluminium in plasma compared with that in aqueous solution is indeed due to the binding of aluminium to high Mr material (proteins). In contrast, however, in an aqueous buffered (pH 7.4) solution containing 28,200 ng of aluminium/ml, only 1.05 +/- 0.09% was ultrafilterable. This indicates insolubility (i.e. colloid formation) of the aluminium at this high concentration. The same percentage (1.06 +/- 0.13) was ultrafilterable from plasma from the high-dose (800 micrograms) aluminium group with a plasma aluminium concentration of 19,800 +/- 2956 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal Handling of Aluminium

“…In rats, Lote et al [7] found that endogenous C Al was ∼8% of the simultaneously measured GFR, which accords with the findings of studies using 26 Al [16]. In contrast, data from another investigation in rats indicated a value for endogenous C Al of ∼20% of the GFR [10].…”

“…In order to allow the determination of Al concentrations in the small volumes of tubular fluid obtained, it was necessary to use very high doses of Al. In one, the Al was administered intravenously as aluminium chloride (plasma Al concentration ∼25–120× normal); Al filterability was inversely correlated to its plasma concentration, and ranged from 2 to 8% [11], echoing the in vitrofindings of Lote et al [7]. This low filterability at high concentrations is thought to be a consequence of formation of insoluble complexes [7].…”

“…In one, the Al was administered intravenously as aluminium chloride (plasma Al concentration ∼25–120× normal); Al filterability was inversely correlated to its plasma concentration, and ranged from 2 to 8% [11], echoing the in vitrofindings of Lote et al [7]. This low filterability at high concentrations is thought to be a consequence of formation of insoluble complexes [7]. More recently, a second micropuncture study has been performed using similar plasma concentrations, but with one important difference: the Al was administered as aluminium citrate [12].…”

“…In the only study reported thus far (in rats), in vitro measurements indicated a surprisingly high figure of 60% filtration of endogenous Al [7], although the animals had received a considerable amount of saline and had been subjected to significant blood losses, thereby reducing plasma protein concentration and perhaps increasing the proportion of Al bound to LMM compounds.…”

“…When administered intravenously as aluminium chloride or aluminium sulphate, percentage filterability (measured in vitro) fell progressively as the plasma concentration increased [7, 8], whereas when aluminium citrate was infused, filterability was unaffected by plasma Al concentration, remaining at the relatively high value of ∼80% [9]. In another study, using the same Amicon filtration system, but in which plasma Al was altered by addition of aluminium citrate to the drinking water, the subsequent intravenous infusion of citrate did not increase Al filterability [10].…”