Effects of fish oil on postburn metabolism and immunity.

The metabolic effects and immune responses of different levels of fish oil in enteral formulas for postburn nutritional support were studied. Thirty-seven burned guinea pigs with previously placed gastrostomy feeding tubes were given diets containing 5, 15, 30, or 50% of nonprotein calories as fish oil. These diets were isonitrogenous, isocaloric, and contained identical amounts of vitamins and minerals. After 14 days of enteral feeding, there were no significant differences in resting metabolic expenditure, serum transferrin, and albumin levels. Weight loss was significantly greater in groups receiving 30 and 50% of fish oil compared to groups which received 5 and 15% of fish oil. Carcass weights and liver weights of animals in the two groups that received diets with higher lipid content were also significantly lower. Cell-mediated immunity, macrophage bactericidal indices, and opsonic indices were not different among the groups. This study confirms that diets containing lower levels of lipids are more effective for enteral nutritional support than those containing higher levels. In contrast to linoleic acid rich lipid sources, higher levels of fish oil did not show adverse effects on immunity possibly because it contained high concentrations of omega 3 fatty acids which are not precursors of immunosuppressive prostaglandin E2.

The effect of route of nutrient administration on the nutritional state, catabolic hormone secretion, and gut mucosal integrity after burn injury.

So that the efficacy of route of nutrient administration in thermal injury could be determined, a comparison was made between immediate enteral vs parenteral feedings in burned guinea pigs. Thirty-five guinea pigs underwent both catheter gastrostomy and jugular vein catheterization. On postoperative day 8, burned animals [30% total body surface area (TBSA)] were divided into an intragastrically (ig) fed group (N = 14) and a parenterally (iv) fed group (N = 14). Animals in each group received 175 kcal/kg/day with a solution of identical nutrient value beginning 2 hr after burn. The body weight change until postburn day (PBD) 8 and the average nitrogen balance were significantly better in the ig group than in the iv group. Values were also higher for the iv group than for the ig group in the early postburn period for urinary vanillyl mandelic acid (VMA) (p less than 0.05), plasma cortisol (p less than 0.05), and plasma glucagon (p less than 0.05). Also, the iv group showed reduced mucosal weight and thickness compared to the ig group on PBD 1 (p less than 0.02). There were significant negative correlations between VMA excretion and body weight change, and between plasma cortisol and jejunal mucosal structure (thickness and weight). These findings suggest that immediate postburn enteral nutrition can provide better nutritional support than parenteral nutrition through the maintenance of gut mucosal integrity and the prevention of increased secretion of catabolic hormones.

Lack of effect of enteral antibiotics on the post-burn hypermetabolic response.

Burn patients who survive the initial 24 h following major burn injury commonly develop a marked hypermetabolism. One of the possible mechanisms of this increased metabolic rate is gut translocation of bacteria and endotoxin following burn injury. We attempted to decrease the hypermetabolism by administering various antibiotic and endotoxin binding agents enterally in a burned guinea-pig model. Adult guinea-pigs were given polymyxin B, trimethoprim and sulphamethoxazole, or neomycin and clindamycin, or Kaopectate, sodium deoxycholate, neomycin, clindamycin and polymyxin B. A control group received no drugs. The drugs were administered through a gastrostomy tube beginning the day before burn injury and continuing for 14 days. There was no significant decrease in the resting metabolic rate in any of the treated groups compared to controls. Neither enteral antibiotics nor endotoxin binding agents were able to induce a significant reduction in the post-burn hypermetabolic response in this model.

Carnitine supplementation vs. medium-chain triglycerides in postburn nutritional support.

The effect of dietary supplementation of carnitine on protein metabolism was studied in a burned guinea-pig model. Animals bearing a 30 per cent total body surface area burn were enterally infused with three isocaloric and isonitrogenous diets via gastrostomy feeding tubes for 14 days. Two diets contained safflower oil (long-chain triglycerides, LCT) and another diet contained medium-chain triglycerides (MCT) as their lipid sources (30 per cent of total calories as lipid). L-Carnitine was added to one of the two diets containing safflower oil. There were no significant differences in nitrogen balance, urinary excretion, serum albumin or transferrin among the three groups. However, the use of MCT in place of LCT appeared to increase liver weight and liver nitrogen. In this model, carnitine supplementation did not enhance the nitrogensparing effect of fat following burn injury.

The effect of the thromboxane synthetase inhibitor Dazmegrel (UK-38,485) on wound healing, dermal ink perfusion and skin blood flow measurements in deep partial thickness burns.

A guinea-pig model was used to evaluate the effect of Dazmegrel (UK-38,485), a new highly selective inhibitor of thromboxane synthetase, on burn wound healing. Dazmegrel had a beneficial effect on wound healing when given systemically at a dosage of 3.4 mg kg-1 day-1 but higher doses had no effect. There was no change in dermal perfusion measured by India ink injection or by 133Xe injection in any of the groups receiving parenteral Dazmegrel. Neither was the number of hair follicles in the healing burn wound significantly different between the treated and control animals. When Dazmegrel was applied topically, it inhibited wound healing. These findings are consistent with previous reports from different laboratories that prostaglandin inhibitors impair healing of the burn wound when applied topically but improve wound healing when given parenterally. The present study further suggested that the improvement in wound healing in this model was not mediated by improved dermal perfusion.