Ajcn28285 1532..1540

Background: Although the protein catabolic effects of metabolic acidosis are well established, it is unclear whether the entire reference range of arterial pH (7.37–7.44) is equivalent for protein balance. Objective: We undertook this study to test the hypothesis that in patients undergoing automated peritoneal dialysis, an arterial pH of 7.43–7.45, as compared with a pH of 7.36–7.38, is associated with more-positive nitrogen balances. Design: Eight stable subjects (5 men) aged 43.16 15.3 y completed a randomized, crossover nitrogen balance study for 42 d. Arterial pH was varied by changing the daily doses of sodium citrate/citric acid and ammonium chloride. Results: The subjects attained mean (6SD) arterial pH values of 7.37 6 0.01 and 7.44 6 0.02 during the low-normal and highnormal pH phases, respectively. The higher arterial pH was associated with higher net nitrogen balances (3.22 6 1.37 compared with 2.29 6 2.18 g/d; P = 0.06), lower serum urea nitrogen (54.1 6 13.7 compared with 64.46 20.2 mg/dL; P = 0.01), higher fasting leucine flux (P = 0.02), and increased fasting total-body protein synthesis (P = 0.01) and degradation (P = 0.02). In 7 of 8 study subjects, nitrogen balances were more positive at the higher arterial pH (P = 0.004). There were no significant changes in anthropometric measurements, other biochemical measurements, and the mRNA content of selected proteins in skeletal muscle. Conclusion: This study suggests that in most stable automated peritoneal dialysis patients, a mean arterial pH of 7.44, as compared with 7.37, is associated with more-positive nitrogen balances. This trial was registered at clinical trials.gov as NCT00586131. Am J Clin Nutr 2009;90:1532–40.