Age and protein malnutrition: effects on the febrile response.

Elderly hospitalized patients frequently do not mount a vigorous febrile response. This diminished response could be due to the combined effects of age and protein malnutrition, a common problem in the elderly. We studied the effect of mild protein deprivation on the febrile response to interleukin-1 (IL-1) and endotoxin in young, middle-aged, and elderly Fischer rats. In each age group, rats received either a standard (23% casein) or low protein (8% casein) diet for 5 weeks (young rats) or 8 weeks (middle-aged and elderly rats). Each rat received an intraperitoneal injection of IL-1, 10 micrograms/kg endotoxin, or 100 micrograms/kg endotoxin and temperatures were measured over 6 h by implanted biotelemetry devices. Protein deprivation decreased the febrile response to IL-1 in all age groups and to endotoxin only in the young and middle-aged rats. Increasing age along did not decrease the febrile response to either pyrogen. Increasing age and protein deprivation did not have an additive effect in decreasing the febrile response to IL-1 or endotoxin.