Oral arginine supplementation does not affect lymphocyte proliferation during endotoxin-induced inflammation in rats

Earlier studies from this laboratory were unable to confirm reported immunostimulatory effects of supplemental dietary arginine on healthy, unstressed young or aged rats. The present study was undertaken to determine effects of oral arginine supplementation on in vitro measures of immune function using a stressed rat model. The stressor used was intraperitoneal injection of bacterial lipopolysaccharide (1 mg/kg body wt). Four-month-old male Sprague-Dawley rats were placed in either a control or an arginine-supplemented (7.5 g/L arginine-HCl in drinking water) group for 7 d, after which control and supplemented rats received injections of endotoxin or phosphate-buffered saline. Rats were killed 3 d following injections. Endotoxin treatment resulted in lower food intake, less thymic cellularity and greater splenic weight. Endotoxin injections also enhanced proliferative response of rat splenocytes to pokeweed mitogen (1 mg/L) and lipopolysaccharide (25 and 100 mg/L) and enhanced response of thymocytes to concanavalin A (10 mg/L), phytohemagglutinin (25 and 100 mg/L) and pokeweed mitogen (1 mg/L). Supplemental arginine did not reduce thymic weight loss or influence mononuclear cell proliferation or interleukin-2 production in the presence or absence of endotoxin stress. These data indicate no benefit of arginine supplementation during endotoxin stress in rats.