Muscle Protein Metabolism of Rats in Surgical Trauma

Abstract

The effects of decreased food intake and degree of surgical trauma on total, myofibrillar and sarcoplasmic muscle protein synthesis and degradation were assessed in two experiments (A and B). Trauma consisted of an abdominal incision with or without hysterectomy. The degree of trauma in experiment B was increased relative to that in experiment A by extending the length of the incision, operative manipulation and time required to perform the surgery. To account for postoperative diminutions in food intake on protein turnover, a group of nonoperated rats were pair-fed to the level of food consumed by hysterectomized rats. Traumatized rats in experiment B lost more weight, ate less, and had a lower muscle total protein concentration than corresponding rats in experiment A, confirming a more severe trauma in experiment B. In both experiments, trauma depressed total protein content of muscle. Synthesis was measured by the incorporation of L-[U-¹⁴C] tyrosine from a single meal into total, sarcoplasmic and myofibrillar proteins of gastrocnemius muscle. Degradation was calculated as the difference between the growth rate and the synthetic rate. Synthetic rate (k_s) of total protein was depressed by surgical trauma; the more severe the trauma, the greater the depression. In mild trauma, the depression in k_s was due only to a decrease in sarcoplasmic protein synthesis (k_e), whereas with more severe trauma, synthetic rates of both sarcoplasmic (k_es ) and myofibrillar (k_em) proteins were decreased. Protein degradation (k_d,) was increased on day 2 in experiments A and B, had returned to control values on day 4 in experiment A and had decreased below control values in experiment B. Postoperative food restriction did not alter muscle protein turnover rates although growth rate was reduced. ( Journal of Parenteral and Enteral Nutrition 12:445-451, 1988)