1. Tumour necrosis factor-α is produced in response to inflammatory stimuli. Fish oil can suppress the production and actions of cytokines. Little information is available on the effects of other fats on cytokine biology. We compared the effects of fats, with a wide range of fatty acid characteristics, on the effects of tumour necrosis factor-α on protein and zinc metabolism in rats.

2. Weanling rats were fed for 8 weeks on diets containing 10% fat in the form of corn, fish or coconut oils or butter before an intraperitoneal injection of recombinant human tumour necrosis factor-α was given. Measurements were made 24 h after the injection.

3. In rats fed corn oil, food intake was reduced by 62% and rates of protein synthesis were increased by 86, 32 and 39% in the liver, lung and kidney, respectively. Zinc concentrations increased by 23% in the liver but decreased by 10% in the kidney. Plasma caeruloplasmin and complement C3 levels increased by 25% and 28%, respectively, and plasma albumin level decreased by 24%.

4. Fish oil prevented the increase in hepatic protein synthesis and changed the response of protein synthesis in lung and kidney to a decrease. Changes in hepatic and renal zinc concentrations were prevented. The response of the plasma caeruloplasmin level was unaltered but those of the plasma complement C3 and albumin concentrations were prevented.

5. Coconut oil and butter, although similarly low in linoleic acid, differed in their modulatory effects. With the exception of the rise in the plasma complement C3 concentration, all responses were prevented or greatly inhibited in rats fed butter. In rats fed coconut oil the increase in liver protein synthesis was reduced but that in the lung and kidney was unaffected. Changes in hepatic zinc concentration were unaffected but those in renal zinc concentration were prevented.

6. Fish and coconut oils and butter reduced the intensity of anorexia caused by tumour necrosis factor-α. The extent to which fats rich in (n-3) polyunsaturates or poor in linoleic acid modulate the metabolic response to tumour necrosis factor-α depends upon additional fatty acid characteristics.

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