Trauma decreases leucine enkephalin hydrolysis in human plasma

Plasma hydrolysis of leucine enkephalin was evaluated, together with several cellular immune parameters, in a homogeneous group of human subjects who had undergone severe trauma (proximal femur fracture); data obtained were compared with those obtained in an age-matched control group. In the experimental group, immediately after hospitalization, substrate hydrolysis was reduced with respect both to the control subjects and the same patients 4 weeks after the trauma. Chromatographic separation of the enzymes active on leu-enkephalin showed that the reduction of substrate hydrolysis is mainly attributable to the decrease in the activity of enkephalin-degrading enzymes, principally of aminopeptidases, per se, whereas the role of the low-molecular-weight plasma inhibitors is only minor. In the same subjects, several of the immunological parameters measured underwent modifications that may be considered stress related. However, the absence of a quantitative relationship between reduction in hydrolysis and modifications of immune parameters does not support the hypothesis of a direct relationship between these two sets of data.