Does increasing blood pH stimulate protein synthesis in dialysis patients?
Although the mechanism of muscle wasting in end-stage renal disease is not fully understood, there is increasing evidence that acidosis induces muscle protein degradation and could therefore contribute to the loss of muscle protein stores of patients on hemodialysis, a prototypical state of chronic metabolic acidosis (CMA). Because body protein mass is controlled by the balance between synthesis and degradation, protein loss can occur as result of either increased breakdown, impaired synthesis, or both. Correction of acidosis may therefore help to maintain muscle mass and improve the health of patients with CMA. We evaluated whether alkalizing patients on hemodialysis might have a positive effect on protein synthesis and on nutritional parameters. Eight chronic hemodialysis patients were treated daily with oral sodium bicarbonate (NaHCO(3)) supplementation for 10-14 days, yielding a pre-dialytic plasma bicarbonate concentration of 28.6 +/-1.6 mmol/l. The fractional synthesis rates (FSR) of muscle protein and albumin were obtained by the L-[(2)H(5)ring]phenylalanine flooding technique. Oral NaHCO(3 )supplementation induced a significant increase in serum bicarbonate (21.5 +/- 3.4 vs. 28.6 +/- 1.6 mmol/l; p = 0.018) and blood pH (7.41 vs. 7.46; p = 0.041). The FSR of muscle protein and the FSR of albumin did not change significantly (muscle protein: 2.1 +/- 0.2 vs. 2.0 +/- 0.5% per day, p = 0.39; albumin: 8.3 +/- 2.2 vs. 8.6 +/- 2.5% per day, p = 0.31). Plasma concentrations of insulin-like growth factor 1 decreased significantly (33.4 +/- 21.3 vs. 25.4 +/- 12.3 nmol/l; p = 0.028), whereas thyroid-stimulating hormone, free thyroxin and free triiodothyronine did not change significantly and nutritional parameters showed no improvement.
In contrast to other findings, raising the blood pH of dialysis patients was not associated with a positive effect on albumin and muscle protein synthesis, or nutritional and endocrinal parameters.