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The effects of acute pH changes on whole body leucine kinetics (1-13C-leucine infusion technique) were determined in normal subjects. Plasma insulin, glucagon, and growth hormone concentrations were kept constant by somatostatin and replacement infusions of the three hormones. When acidosis was produced by ingestion of NH4Cl (4 mmol kg-1 p.os; n = 8) arterialized pH decreased within 3 h from 7.39 +/- 0.01 to 7.31 +/- 0.01 (P less than 0.001) and leucine plasma appearance increased by 0.13 +/- 0.04 mumol kg-1 min-1 (P less than 0.02); in contrast, when alkalosis was produced by intravenous infusion of 4 mmol kg-1 NaHCO3 (n = 7, pH 7.47 +/- 0.01), leucine plasma appearance decreased by -0.09 +/- 0.04 mumol kg-1 min-1 (P less than 0.01 vs. acidosis). Whole body leucine flux also increased during acidosis compared to alkalosis (P less than 0.05), suggesting an increase in whole body protein breakdown during acidosis. Apparent leucine oxidation increased during acidosis compared to alkalosis (P = 0.05). Net forearm leucine exchange remained unaffected by acute pH changes. Plasma FFA concentrations decreased during acidosis by -107 +/- 67 mumol l-1 (P less than 0.05) and plasma glucose increased by 1.90 +/- 0.25 mmol l-1 (P less than 0.02); in contrast, alkalosis resulted in an increase in plasma FFA by 83 +/- 40 mumol l-1 (P less than 0.02; P less than 0.01 vs. acidosis), suggesting an increase in lipolysis; plasma glucose decreased compared to acidosis (P less than 0.01). The data demonstrate that acute metabolic acidosis and alkalosis, as they occur in clinical conditions, influence protein breakdown, and in the opposite direction, lipolysis.

The effects of endotoxin (E) administration on whole body protein and glucose metabolism were studied in normal volunteers. Injection of 4 ng/kg Escherichia coli E iv resulted in a relative increase in leucine flux (1-13C-leucine infusion technique) compared to controls [+0.12 +/- 0.10 vs. -0.45 +/- 0.23 mumol/kg.min after 360 min, P = 0.028, analysis of variance (ANOVA)], indicating increased proteolysis. Nonoxidative leucine flux was higher after E than after saline administration (0.08 +/- 0.11 vs. -0.47 +/- 0.18 mumol/kg.min, P = 0.007, ANOVA), suggesting increased amino acid incorporation into proteins. E caused a transient decrease of plasma glucose concentration (by 0.5 +/- 0.1 mmol/L after 150 min; P < 0.004 vs. saline controls) due to a relative increase in disappearance compared to appearance of glucose (6,6 D2-glucose infusion technique). These alterations were associated with increases in plasma concentrations of ACTH, beta-lipoprotein (beta-LPH), GH, cortisol, epinephrine, free fatty acid, beta-hydroxybutyrate, and decreases of plasma insulin. Pretreatment with ibuprofen, a cyclooxygenase inhibitor, blunted the effects of E on whole body leucine flux (P < 0.05 vs. E) and on nonoxidative leucine flux (P < 0.05 vs. E) but enhanced the E-induced decrease of plasma glucose concentration (P < 0.004 vs. E), due to a relative increase in glucose disappearance compared to appearance (P = 0.02). The increases in counterregulatory hormones (ACTH, beta-LPH, GH, cortisol, epinephrine) were also attenuated by ibuprofen. Thus, acute endotoxinemia results in a redistribution of whole body proteins due to an increase in both protein breakdown and amino acid incorporation into proteins and in decreased plasma glucose concentrations. The ibuprofen data suggested that these effects of E on leucine kinetics, but not on glucose metabolism, were prostaglandin E2-mediated.

To investigate whether changes in systemic pH influence ketone body production or utilization, total ketone body (TK) kinetics were measured with [3-14C]acetoacetate and D-beta-[1,3-13C2]hydroxybutyrate tracers in overnight fasted subjects during metabolic alkalosis (NaHCO3 infusion) or acidosis [NH4Cl ingestion or arginine (Arg)-HCl infusion]. Somatostatin, with insulin, glucagon, and growth hormone replacement, was infused in all studies. Blood pH and HCO3- (mM) increased from baseline (0-30 min) to 180-210 min by 0.08 +/- 0.02 and 7 +/- 1 with NaHCO3 and decreased by 0.08 +/- 0.2 and 7 +/- 1 or 5 +/- 1 with NH4Cl or Arg-HCl (all P less than 0.005). Over this period blood TK (microM) differed between the NaHCO3 (+198 +/- 65) and both NH4Cl (-90 +/- 53) and Arg-HCl (-154 +/- 55) (P less than 0.05). These changes resulted from parallel alterations in TK production rate of appearance (Ra TK, mumol.kg-1.min-1), because changes from baseline in Ra 14C TK also differed between NaHCO3 (+1.9 +/- 0.8) and NH4Cl (-1.0 +/- 0.6) and Arg-HCl (-2.0 +/- 0.5) (P less than 0.05). Ra TK calculated with single- or dual-tracer techniques were similar. Blood free fatty acids (FFA) increased with NaHCO3, and FFA and glycerol decreased with NH4Cl and Arg-HCl, suggesting that FFA availability mediated the pH effects on hepatic ketogenesis. These results demonstrate that modest changes in systemic pH modify FFA availability and TK production rates.

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