Abstract
Injury, particularly burn injury, is associated with hypermetabolism, weight loss, and catabolism. Recent studies have suggested that selective β-2 adrenergic agonists may have anabolic properties. In this study, 38 Sprague-Dawley rats were divided into five groups: Cont-SAL (n = 8) served as the saline-control group; Cont-CLE (n = 8) received twice-daily injections of clenbuterol (1 mg/kg subcutaneously), a selective β-2 agonist for 22 days and served as a second control group; Burn-SAL (n = 8) was subjected to a 30% body surface area full-thickness open-flame burn; Burn-CLE (n = 8) was similarly burned, but also received clenbuterol starting on postburn day 1; Burn-NAD (n = 6) was also similarly burned but received the beta antagonist, nadolol (5 mg/ kg subcutaneously), once daily for 22 days starting on postburn day 1. Daily weights, food, and water consumption were measured. Resting energy expenditure (REE) was determined for all rats on postburn days 7 to 9 and again 20 to 22. On postburn day 22, rats were killed and plasma-free amino acid levels, gastrocnemius muscle wet and dry weights, and muscle protein contents were determined. Data were analyzed using analysis of variance with Tukey and Newman-Keuls multiple range tests.
All three groups of burned rats had higher food and water consumption than the control groups, but there was no significant difference in consumption among the three burned groups. Body weight gain was higher in Burn-CLE than in Burn-SAL or Burn-NAD rats and was equal to body weight gain on Cont-SAL and Cont-CLE rats. REE 1 and 3 weeks after the burn, was significantly higher in all burn groups, when compared to the control groups; among the burn groups, the REE of Burn-CLE was significantly elevated at 1 week when compared to Burn-SAL and Burn-NAD. The mean dry weight of the gastrocnemius muscle was significantly decreased in Burn-SAL and Burn-NAD vs the control groups. However, Burn-CLE demonstrated normal muscle dry weight and muscle protein content. Analysis of plasma amino acid concentrations demonstrated that clenbuterol reversed few of the changes induced by the burn injury, but did elevate the concentrations of several amino acids in nonburned rats. These results suggest that clenbuterol, a selective β-2 agonist, may be useful in helping to preserve muscle mass after injury.
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