Comparative effects of thermal and surgical trauma on rat muscle protein metabolism.

A modified intraperitoneal pool flooding technique, employing L-3H-tyrosine, was developed for measuring muscle protein synthetic rates following traumatic injury. Sufficient radiolabeled tyrosine was injected intraperitoneally to effect a six-fold increase in plasma tyrosine concentration (124-800 microM) resulting in constant, sustained specific radioactivities in plasma- and intracellular-free tyrosine pools. Localized vs systemic effects of thermal and surgical trauma on gastrocnemius muscle protein turnover were assessed 2 and 4 days postinjury. Thermal trauma increased total, myofibrillar, and sarcoplasmic muscle protein synthesis (44%) and protein degradation (300%). Conversely, surgical trauma decreased synthesis of total (24%), myofibrillar (14%), and sarcoplasmic (43%) muscle proteins without altering protein degradation. Short-term restriction of pair-fed controls did not affect either aspect of protein turnover.