Protein turnover in patients before and after elective orthopaedic operations.

Whole body protein turnover was measured in 11 patients before and after elective orthopaedic operations be giving 15N-glycine orally every 4 hours for 32 hours. The patients were maintained throughout on a constant protein intake. In 2 control subjects a comparison was made between intermittent dosage and continuous infusion of 15N-glycine for the estimation of total protein 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 -0-52 +/- 1-31 g/d (mean +/- s.d.) before operation and -7-51 +/- 4-5 g/d after operation. The rate of protein synthesis fell from 3-83 +/- 0-73 g kg-1 d-1 before operation to 2-94 +/- 0-83 g kg-1 d-1 after operation. This difference is statistically significant (0-05 greater than P greater than 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.