Urinary excretion and efflux from the leg of 3-methylhistidine before and after major surgical operation

Changes in the effluxes from the leg of 3-methylhistidine and tyrosine were studied in relation to alterations in the 24-hour excretion of 3-methylhistidine and total nitrogen in 11 patients before and after undergoing major surgical operation. On the first day after operation, efflux of 3-methylhistidine from the leg was significantly decreased by 40% compared to preoperative values. In contrast, tyrosine efflux was doubled at the same time as a transient 20% increase in oxygen uptake of the leg and a marked increase in catecholamine excretion were observed. These changes coincided with a 40% elevation in the excretion of both 3-methylhistidine and nitrogen. Leg metabolism returned to the preoperative pattern within a week. These results suggest that the loss of amino acids from the lean tissues of the leg is the result of a fall in protein synthesis accompanied by an adaptive fall in protein breakdown. Although the increase in nitrogen excretion in response to major surgical trauma reflects the negative amino acid balance of skeletal muscle, the changes in urinary 3-methylhistidine do not correlate with changes in efflux of 3-methylhistidine from the leg. These results suggest that the use of 3-methylhistidine excretion as a specific index of skeletal muscle protein breakdown in postoperative patients may be invalid. Tissues other than skeletal muscle appear to make a substantial contribution to the 3-methylhistidine excretion postoperatively.