Elevated plasma binding cannot account for the burn-related d-tubocurarine hyposensitivity

Hyposensitivity to the nondepolarizing muscle relaxant d-tubocurarine (dTc) has been reported during the treatment of burn injury. The authors present here evidence obtained by the technique of equilibrium dialysis, that a 1.7-fold increase in dTc binding by plasma constituents occurs one to two weeks following burn injury, a timing which coincides with the onset of clinical hyposensitivity to dTc. Plasma drawn from burned patients at least one week post-burn exhibited a mean dTc-binding capacity of 5.7 +/- 0.9 nmol/g total protein compared to 3.4 +/- 0.7 nmol/g for normal plasma at a final free concentration of 0.5 microM (0.34 microgram/ml). Calculation suggests that increased plasma binding can account only for a fraction of the observed hyposensitivity; other unidentified factors must also be involved. The elevated binding capacity of plasma drawn from burned patients seems unrelated to any of the quantitative or gross qualitative changes in plasma protein profile reported here. Preliminary experiments with metocurine (mTc) show directional changes similar to dTc.