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 microg.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 FD(Al) (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 FD(Al) at the early distal site and that in the final urine; however, in the high-dose group, FD(Al) 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.
Shirley
David G
DG
Centre for Nephrology and Department of Physiology, Royal Free and University College Medical School, Royal Free Hospital, London NW3 2PF, UK. david.shirley@ucl.ac.uk
Walter
Mary F
MF
Walter
Stephen J
SJ
Thewles
Andrew
A
Lote
Christopher J
CJ
D000042:Absorption; D000535:Aluminum / Q000097:blood / Q000493:pharmacokinetics*; D000818:Animals; D019343:Citric Acid / Q000008:administration & dosage / Q000097:blood; D004334:Drug Administration Schedule; D005919:Glomerular Filtration Rate / Q000502:physiology; D007262:Infusions, Intravenous; D007444:Inulin / Q000032:analysis; D007668:Kidney / Q000378:metabolism*; D007686:Kidney Tubules, Distal / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008138:Loop of Henle / Q000378:metabolism; D008297:Male; D011677:Punctures / Q000379:methods; D051381:Rats; D017208:Rats, Wistar
D019343:Citric Acid; D007444:Inulin; D000535:Aluminum; C455846:aluminum citrate