Erythrocyte sodium/lithium countertransport and renal lithium clearance in a random sample of untreated middle-aged men.
1. It has been proposed that the enhanced erythrocyte Na+/Li+ countertransport observed in many patients with essential hypertension could be a marker of abnormal renal proximal tubular function. We thus investigated the relationship of blood pressure and Na+/Li+ countertransport to an index of proximal tubular function such as renal Li+ clearance. 2. The study was carried out in a sample of 299 untreated male subjects (aged 21-59 years) randomly selected from a population at work. Na+/Li+ countertransport was measured in a representative sub-group of 176 men. 3. We did not detect statistically significant correlation of either blood pressure or Na+/Li+ countertransport (Vmax) with fractional excretion of Li+, while confirming the existence of a significant continuous association of blood pressure and body mass index with Na+/Li+ countertransport (P less than 0.01). 4. A sub-sample of 57 participants belonging to the lowest or the highest quintiles of Na+/Li+ countertransport distribution repeated the Li+ clearance study after moderate Na+ restriction. 5. Although fractional excretions of Na+ and Li+ were reduced on the low Na+ diet (both P less than 0.001), they did not differ significantly between groups. 6. Our results are at variance with the findings of a recent case-control study in a young age group and suggest that further studies are necessary before a conclusion can be drawn as to the suitability of Na+/Li+ countertransport as a marker of Na+ reabsorption in the renal proximal tubule.
Strazzullo
P
P
Institute of Internal Medicine and Metabolic Diseases, Clinica Medica, 2nd Medical School, University of Naples, Italy.
Cappuccio
F P
FP
Trevisan
M
M
Iacoviello
L
L
Iacone
R
R
Jossa
F
F
Giorgione
N
N
Farinaro
E
E
Mancini
M
M
D000328:Adult; D001693:Biological Transport, Active; D001794:Blood Pressure; D003401:Creatine / Q000652:urine; D004912:Erythrocytes / Q000378:metabolism*; D005919:Glomerular Filtration Rate; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008094:Lithium / Q000097:blood / Q000652:urine*; D008297:Male; D008875:Middle Aged; D011897:Random Allocation; D012964:Sodium / Q000097:blood / Q000652:urine*
D008094:Lithium; D012964:Sodium; D003401:Creatine