The effects of exercise and food restriction on the acute phase response.

Abstract

Regular release of cytokines during endurance exercise training may enhance nonspecific immune response and food restriction may interfere with this beneficial effect. The hypothesis that voluntary running and moderate food restriction alter the acute phase response (APR), one index of nonspecific host defense, was tested in a hamster model. Independent variables were diet (ad libitum or restricted), activity (sedentary or voluntary running), and injection (saline or lipopolysaccharide (LPS)). Dependent variables were fever (a clinical symptom of the APR), circulating interleukin-6 (IL-6, a cytokine mediator of the APR), serum amyloid A (SAA, an acute phase protein), serum iron (hypoferremia occurs during the APR), and cortisol (a hormone induced during the APR) measured by biotelemetry, B-9 cell bioassay, direct ELISA, colorimetric analysis, and radioimmunoassay, respectively. Voluntary running did not alter the APR to injection of a low dose of LPS as estimated by the markers of the APR measured in this study. However, exercise chronically elevated body temperature 0.3 to 0.5$\sp\circ$C in hamsters. This elevation may afford benefits to the nonspecific immune system associated with increased temperature such as enhanced leukocyte mobility. Food restriction lowered body temperature and therefore may depress any immunoprotective benefits associated with normal or elevated body temperature. Cortisol was mildly elevated by food restriction. Although pharmacological or stress levels of glucocorticoids are immunosuppressive, small elevations of glucocorticoids may be protective because of their role in mobilizing endogenous fuels. Following LPS, food restriction depressed the elevation of SAA without restricting the fever, elevations in IL-6 and cortisol, or hypoferremia. The consequences of a depressed SAA response are unknown. Exercise combined with food restriction held mean body temperature near the level of the freely fed sedentary animals and thus would negate any immunosuppressive effect of low temperature due to food restriction. Following LPS injection, exercise combined with food restriction did not affect fever or IL-6 response, and did not alter the depressed SAA and elevated cortisol responses seen with food restriction alone, but did significantly hinder hypoferremia. Thus exercise combined with food restriction may depress resistance to iron-dependent microorganisms.