Protein turnover in patients before and after elective orthopaedic operations

ABSTRACT

Whole body protein turnover was measured in 11 patients before and after elective orthopaedic operations by giving 15N-glycine orally every 4 hours for 32 hours. The patients were maintained throughout on a constant protein intake. In two control subjects a comparison was made between intermittent dosage and continuous infusion of 15N-glycine for the estimation of total turnover. With intermittent dosage the 15N abundance in urinary urea reached a constant level after about 24 hours. Rates of total protein synthesis and breakdown were calculated from the 15N abundance at the plateau level. After surgery there was a moderate increase in urinary N output. The apparent N balance (intake - urinary N) was -0.25 ñ 1.31 g/d (mean ñ s.d.) before operation and =7.51 ñ 4.5g/d/ after operation. The rate of protein synthesis fell from 3.83 ñ 0.73g kg-1d-1 before operation to 2.94 ñ 0.83 g kg-1d-1 after operation. This difference is statistically significant (0.05 > p > 0.01). There was no significant change in the rate of protein breakdown. The possibility remains that a block in protein synthesis, probably mainly in muscle, may be partly responsible for the so-called 'catabolic' loss of nitrogen after injury, but this has not been proved. (AU)