Tubular function by lithium clearance, plasma amino acids and hormones following a meat meal in childhood

Tubular function was measured by lithium clearance (C<inf>Li</inf>) and by its derived formulae before and after the transient increase (lasting 90min) in glomerular filtration rate (GFR) following a meat meal (2g protein/kg body weight) in 12 normal children. Three baseline and 4 clearances after the meal were obtained, each lasting 30min. The mean baseline C<inf>u</inf> was 23.1 ± 1.64ml/min/1.73m². At peak GFR response (60min from starting the meal), C<inf>Li</inf> averaged 27.6±2.4ml/min/1.73m² (p<0.025vs. baseline) and it was further increased (32.2±5.04 ml/min/1.73m², p<0.01 vs. baseline) 120min after starting the meal, while GFR returned to baseline values. Fractional lithium excretion averaged 0.23±0.04 at baseline and increased continuously after the meat meal and. at completion of the study, it averaged 0.38±0.07 (p<0.025vs. baseline). The distal absolute and fractional sodium reabsorption increased throughout the studies following the meal and peaked at 120min. The functional changes were associated with a statistically significant increase in the plasma concentration of insulin, glucagon, and total amino acids after the meal. The latter at the end of the study was almost doubled (5,600 ±780 versus 3,200μM at baseline, p<0.01). The data indicate that the tubulo glomerular feedback mechanism operates normally after a meat meal. The finding on increased distal sodium reabsorption might point to the existence of an insulin-dependent mechanism. © 1991 S. Karger AG, Basel.