INCREASED CONTRIBUTION BY MYOFIBRILLAR PROTEIN TO WHOLE-BODY PROTEIN BREAKDOWN ACCORDING TO SEVERITY OF SURGICAL STRESS

A study was conducted to clarify the contribution by myofibrillar prot ein to whole-body protein breakdown in surgically stressed patients. T hirteen patients who underwent esophagectomy (group E) and 22 who unde rwent gastric or colorectal operation (group GC) were studied. Patient s were all male and younger than 65 y old. Whole-body protein breakdow n was determined using constant infusion of N-15-glycine. Urinary excr etion of total catecholamines and 3-methylhistidine (3-MH) were measur ed. Amino acid composition of femoral arterial and venous blood was al so analyzed. All the patients were fed exclusively by total parenteral nutrition providing 1.5 g protein and 40 kcal . kg(-1). d(-1) through out the study. Whole-body protein breakdown increased significantly in group E (P < 0.01) and group GC (P < 0.05) on the 3rd postoperative d ay. The increase was significantly greater in group E than group GC (P < 0.01). Urinary excretion of 3-MH also increased significantly in gr oup E (P < 0.01) and in group GC (P < 0.01) on the 3rd postoperative d ay. 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 ( mu mol/g), which is a indicator for the contribution of myofibrillar p rotein to the whole-body protein breakdown, increased significantly fr om 0.84 +/- 0.30 of preoperative value to 1.79 +/- 0.38 in group E (me an +/- SD; P < 0.01) and 1.42 +/- 0.18 in group GC (P < 0.05) on the 3 rd postoperative day. This ratio was significantly higher in group E ( P < 0.05). Furthermore, the ratio of myofibrillar to whole-body protei n breakdown correlated significantly with urinary excretion of total c atecholamines (r = 0.546; P < 0.01). Therefore, the contribution of my ofibrillar protein to whole-body protein breakdown increased proportio nately with the severity of surgical stress. On the other hand, femora l-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 breakd own of total myofibrillar proteins and both correlate with the severit y of stress. From these data, it may be suggested that the contributio n of skeletal muscle to whole-body protein catabolism is increased pos toperatively, and that the increase is correlated with the severity of surgical stress.