Effects of chronic exercise conditioning on thermal responses to lipopolysaccharide and turpentine abscess in female rats

Abstract

Chronic exercise conditioning has been shown to alter basal thermoregulatory processes as well as the response to inflammatory agents. Two such agents, lipopolysaccharide (LPS) and turpentine (TPT) are inducers of fever in rats. LPS, given intraperitoneally (i.p.), involves a systemic inflammatory response whereas TPT given intramuscularly (i.m.) elicits a localized inflammation. We assessed if chronic exercise training in the rat would alter the thermoregulatory response to LPS and TPT. Core temperature ( T c ) and motor activity were monitored by radiotelemetry. Female Sprague Dawley rats were divided into two groups (trained and sedentary) and housed at an ambient temperature of 22°C. Animals voluntarily trained on running wheels for 8 weeks. In the first study, trained and sedentary female rats were injected i.p. with LPS (50 μg/kg) or an equal volume of 0.9% normal saline. In another study, trained and sedentary female rats were injected i.m. with TPT (10 μl)/rat or an equal volume of 0.9% normal saline. The time course of the LPS fever was very short compared to TPT. TPT injected animals displayed a smaller but more prolonged fever compared to LPS; however, training accentuated the febrile response to LPS (Δ T c =0.6°C in sedentary and 1.2°C in trained). Training had a slight suppression on TPT-induced fever during the daytime but had no effect on motor activity or nighttime T c . In contrast, exercise training led to a marked increase in the pyrogenic effects of LPS. We conclude that the effect of exercise training and source of infection (i.e., systemic versus localized in muscle) on fever is directly linked to type of pyrogenic agent.