Effects of Hemorrhage on Whole Body Protein Catabolism in Pigs

Introduction: Hemorrhage constitutes 40-50% of injury related deaths in civilian trauma and on battlefields. While some studies have investigated the effects of hemorrhage on the coagulation proteins, the effects of hemorrhage on total protein metabolism is unclear. The purpose of this study was to investigate changes of whole body protein degradation following a moderate hemorrhage in a swine model.

Methods: Following overnight fasting, twelve pigs (36.1 ± 1.7 kg) were anesthetized, catheterized for measurements, infusions and blood sampling and randomly allocated into the control (n=6) and the hemorrhage (n=6) groups. Hemorrhage was induced by removal of 35% of the total blood volume from the left femoral artery in the hemorrhage group over a 30 min period, followed by resuscitation with lactated Ringer's solution (3 times the hemorrhage volume). Afterwards, a constant infusion of stable isotope 1-13C-phenylalanine was performed for 6h. During the 6h infusion, mean arterial pressure (MAP) and heart rates were recorded and blood samples were taken hourly for biochemical measurements. Blood glucose and lactate concentrations were analyzed using YSI 2300 STAT Plus. Whole body protein breakdown was assessed by the rate of appearance of phenylalanine in circulation, using the gas chromatography mass spectrometry analysis (GC-MS, model 5973, Hewlett-Packard). A selective ion-monitoring method was used at nominal mass to charge ratio (m/z) of 336 (m+0) and 337 (m+1) for phenylalanine. Data were compared using two-way ANOVA with repeated measurements.

Results: Hemorrhage caused a significant decrease in MAP. At 1h, 2h, and 3h during the infusion, MAP in the hemorrhage group was 100 ± 1 mmHg, 99 ± 1 mmHg, and 99 ± 2 mmHg, respectively, while MAP in the control group was 115 ± 2 mmHg, 114 ± 2 mmHg, and 114 ± 1 mmHg, respectively (all p<0.05). Afterwards, there were no differences in MAP between the two groups. There were no significant differences in heart rate between the two groups during the study. Plasma lactate level was elevated in the hemorrhage group to 1.62 ± 0.14 mM from the control value of 0.85 ± 0.06 mM at 4h (p<0.05). There were no significant changes in blood glucose in either group during the study. After 1h of the isotope infusion, plasma phenylalanine enrichments (which were measured as the tracer to tracee ratio in GC-MS) reached a plateau in both control (18.64% ± 1.86%) and hemorrhage (13.94% ± 0.77%, p<0.05) groups. The rate of appearance of phenylalanine, which reflects whole body protein degradation, was elevated in the hemorrhage group from the control value of 1.20 ± 0.04 µmol/kg/min to 1.46 ± 0.09 µmol/kg/min (p<0.05).

Conclusion: Hemorrhage caused acute acceleration in whole body protein degradation. Additional studies are needed to identify the pathways contributing to the acceleration.

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