Immunologically mediated growth depression in chicks: influence of feed intake, corticosterone and interleukin-1

The effects of an immune response on growth and feed efficiency in chicks and the role of interleukin-1 (IL-1) and corticosterone (Cort) as mediators of the response were investigated. Daily injections of either sheep red blood cells or the inflammatory agent Sephadex resulted in significantly (P less than 0.05) lower rates of weight gain, feed intake and efficiency of feed utilization than controls fed ad libitum, indicating an immunologically mediated stress. Feeding control chicks the same amount of diet as that consumed by immunologically challenged chicks did not completely equalize rates of weight gain. Injections of a crude preparation of IL-1, but not Cort, resulted in weight gain, feed intake and efficiency of feed utilization that were similar to those of immunologically challenged chicks. The concentrations of IL-1 and Cort, measured by bioassay and radioimmunoassay, respectively, in serum from immunologically challenged chicks were significantly higher than in nonchallenged chicks. To determine the influence of IL-1 and Cort on protein accretion in skeletal muscles, the extensor digiti communus and ulnaris lateralis were incubated in the presence of these two hormones at concentrations similar to that seen in serum after an immunologic challenge. Cort did not affect the rate of protein degradation but resulted in rates of protein synthesis that were significantly lower than controls. IL-1 did not affect the rate of protein synthesis but resulted in rates of protein degradation that were about 24% greater than controls.