Is the endogenous antipyretic neuropeptide alpha-MSH responsible for reduced fever in aged rabbits?
The reduced febrile response in aged man has been noted since the beginning of clinical thermometry. Our previous research on aged rabbits and squirrel monkeys disclosed a similar reduced fever, presumably due to a decrease in central receptors for endogenous pyrogen. However, because central alpha-melanocyte stimulating hormone (MSH) appears to have a potent role in physiological control of fever, it may be that increased release of the peptide is responsible for the reduced febrile response in aged animals. To test this idea, antiserum specific to MSH was administered intracerebroventricularly to rabbits of known age. The antiserum given according to three schedules of treatment augmented fever caused by IV injections of interleukin-1 (IL-1) in young (less than 2 years) male and female rabbits. Aged female rabbits (3-5+ years) and females aged 2-3 years showed significant augmentation of fever only after pretreatment plus acute injection of antiserum. A single ICV injection of MSH (200 ng) reduced fever in all groups with the greatest antipyretic effect in the aged females. The results indicate that while aged rabbits have an increased antipyretic response to central MSH, binding of the endogenous peptide does not result in marked increases in fever in these animals. Thus, whereas a change in central MSH sensitivity may contribute to reduced fever in aged homeotherms, a reduction in central pyrogen receptors appears to be the most parsimonious explanation.
Bell
R E
RE
Physiology Department, University of Texas Health Science Center at Dallas 75235.
Feng
J
J
Lipton
J M
JM
D000375:Aging / Q000502:physiology*; D000818:Animals; D005260:Female; D005334:Fever / Q000503:physiopathology*; D007275:Injections, Intravenous; D007276:Injections, Intraventricular; D008297:Male; D011749:Pyrogens / Q000008:administration & dosage / Q000494:pharmacology; D011817:Rabbits; D012737:Sex Factors; D000521:alpha-MSH / Q000502:physiology*
D011749:Pyrogens; D000521:alpha-MSH