Renal aluminium handling in the rat: a micropuncture assessment

Uncertainties exist over the glomerular filtration of aluminium and virtually nothing is known about its segmental handling along the nephron. The present study has used micropuncture, combined with electrothermal atomic absorption spectroscopy, to determine directly the aluminium content of glomerular filtrate and of late PCTs (proximal convoluted tubules) and early distal tubules in anaesthetized Munich–Wistar rats infused with three different doses of aluminium citrate (plasma aluminium concentrations, 2.9±0.1, 5.2±0.4 and 10.0±0.9 μg·ml−1 respectively). Aluminium filtration into Bowman's space was found to be considerably greater than that predicted by an in vitro filtration system: in all three groups it was essentially filtered freely. No significant aluminium reabsorption took place along the PCT, but with every dose the FDAl (fractional delivery of aluminium; tubular fluid:plasma aluminium/inulin concentration ratio) was lower at the early distal site than at the late PCT (P<0.001 in each case), indicating net aluminium reabsorption in the loop of Henle. This reabsorption amounted to 19–26% of the filtered aluminium load. In the low- and medium-dose groups, there was no significant difference between FDAl at the early distal site and that in the final urine; however, in the high-dose group, FDAl in the urine (1.02±0.06) exceeded that at the early distal tubule (0.75±0.04; P<0.001), suggesting aluminium secretion in the distal nephron. The results indicate that aluminium loads, when complexed with citrate, are excreted efficiently owing to a combination of glomerular filtration and minimal reabsorption.

Calorimetric investigations of Al3+(aq), Al(OH)4−(aq), and aluminium–citrate complexes at 298.15 K

We have combined results of earlier measurements leading to equilibrium constants for formation and reaction of aluminum–citrate complexes in aqueous solution at 298.15 K with results of our calorimetric measurements at this same temperature to obtain ΔH values for reactions of Al3+(aq) with citrate ions. Results of some of these calorimetric measurements also lead to a value of ΔH for the reaction Al3+(aq) + 4 OH`(aq) = Al(OH)4−(aq). Keywords: aluminum hydroxide, Al(OH)4−(aq), thermodynamics; aluminium–citrate complexes, thermodynamics; citrate–aluminum complexes, thermodynamics; aluminum (3+, aq), thermodynamics.

Intestinal Absorption of Trace Amounts of Aluminium in Rats Studied with 26Aluminium and Accelerator Mass Spectrometry

1. Until recently studies of intestinal aluminium absorption used pharmacological amounts of stable 27Al. 2. To examine the intestinal absorption of trace amounts of different chemical compounds of aluminium, in the present study we have employed the long half-life isotope of aluminium, 26Al, and accelerator mass spectrometry. Trace amounts of 26Al (2.7–12.1 ng) as the hydroxide, citrate, citrate plus 1 mmol/kg sodium citrate, or maltolate respectively, were administered to four groups of rats (n = 9 per group) by gavage. Blood and urine samples were collected for 5 h and the 26Al content (as a percentage of the administered dose) determined by accelerator mass spectrometry. 3. The 5 h urinary 26Al excretion amounted to 0.1 ± 0.02, 0.7 ± 0.2, 5.1 ± 1.5 and 0.1 ± 0.1% of administered dose in the four groups respectively. There was a strong positive correlation between peak plasma 26Al (r = 0.98) and urinary 26Al excretion in individual animals (P < 0.001). 4. We conclude that the fractional intestinal absorption of trace oral doses of aluminium hydroxide is at least 0.1% (compared with the previous estimate of 0.01% using large 27Al oral loads). Absorption of aluminium citrate given alone is significantly greater (0.7%) and is further increased to 5% by the accompanying sodium citrate, consistent with an enhancing effect of added citrate upon mucosal aluminium permeability. Aluminium maltolate absorption approximates that of aluminium hydroxide (0.1%).