Increased contribution by myofibrillar protein to whole-body protein breakdown according to severity of surgical stress

Abstract

A study was conducted to clarify the contribution by myofibrillar protein to whole-body protein breakdown in surgically stressed patients. Thirteen patients who underwent esophagectomy (group E) and 22 who underwent gastric or colorectal operation (group GC) were studied. Patients were all male and younger than 65 y old. Whole-body protein breakdown was determined using constant infusion of 15N-glycine. Urinary excretion of total catecholamines and 3-methylhistidine (3-MH) were measured. Amino acid composition of femoral arterial and venous blood was also analyzed. All the patients were fed exclusively by total parenteral nutrition providing 1.5 g protein and 40 kcal·kg −1·d −1 throughout the study. Whole-body protein breakdown increased significantly in group E ( P < 0.01) and group GC ( P < 0.05) on the 3rd postoperative day. The increase was significantly greater in group E than group GC ( P < 0.01). Urinary excretion of 3-MH also increased significantly in group E ( P < 0.01) and in group GC ( P < 0.01) on the 3rd postoperative day. The increase was also greater in group E than group GC ( P < 0.01). The ratio of urinary 3-MH excretion to whole-body breakdown protein (μmol/g), which is a indicator for the contribution of myofibrillar protein to the whole-body protein breakdown, increased significantly from 0.84 ± 0.30 of preoperative value to 1.79 ± 0.38 in group E (mean ± SD; P < 0.01) and 1.42 ± 0.18 in group GC ( P < 0.05) on the 3rd postoperative day. This ratio was significantly higher in group E ( P < 0.05). Furthermore, the ratio of myofibrillar to whole-body protein breakdown correlated significantly with urinary excretion of total catecholamines ( r = 0.546; P < 0.01). Therefore, the contribution of myofibrillar protein to whole-body protein breakdown increased proportionately with the severity of surgical stress. On the other hand, femoral-arteriovenous differences of BCAA, Ala, Gln, Tyr, and Phe correlated significantly with the urinary excretion of 3-MH. These data suggest that skeletal muscle protein degradation is proportional to the breakdown of total myofibrillar proteins and both correlate with the severity of stress. From these data, it may be suggested that the contribution of skeletal muscle to whole-body protein catabolism is increased postoperatively, and that the increase is correlated with the severity of surgical stress.