The association of E. coli peritonitis with an impaired and delayed fever response in senescent rats

Infection is one of the leading causes of death in elderly humans, and the importance of the early diagnosis of severe infection is undisputed. In the elderly a delay in diagnosis is often due to a reduced or absent fever. To understand more fully the pathogenesis of fever in senescence, we assessed the febrile response to E. coli peritonitis in 3-, 12-, and 24-month-old rats. Baseline temperatures were unchanged with age. Following infection with 1 x 10(8) CFU E. coli, a fever was evident in 2.8 h in the young, 3.9 h in the 12-month-old rats, and delayed until 5.8 h in the senescent rats. The magnitude of the fever was quantitatively less in the older rats compared with the two younger age groups throughout the time course of the fever. Because beta-adrenergic-mediated thermogenesis in brown adipose tissue has been implicated in the genesis of fever, we also assessed adenylate cyclase activity in this tissue. There was a progressive age-related decrease in both receptor- and postreceptor-stimulated adenylate cyclase activity. Our findings indicate there is both a delay in the onset of the fever and a reduced febrile response in the senescent rats following E. coli infection.