Peripheral administration of alpha-MSH reduces fever in older and younger rabbits.

In these experiments IV, ICV and intra-gastric administration of alpha-MSH reduced fever caused by injections of leukocytic pyrogen (LP). 2.5 micrograms alpha-MSH injected IV reduced fever caused by IV LP, more so in rabbits over 3 yrs old than in those under 2 yrs of age; 5 mg of acetaminophen given IV had no antipyretic effect in either age group. ICV administration of 25 ng alpha-MSH reduced fever caused by IV LP injection in the older but not in the younger rabbits, alpha-MSH given IV (2.5 micrograms) also lowered fever induced by ICV injection of LP in older but not in younger animals. Both older and younger rabbits showed reductions in fever evoked by IV LP after 2.5 mg alpha-MSH was given by gastric tube. The results indicate that this peptide which occurs naturally within the brain has potent antipyretic properties when given systemically, presumably as a result of a central antipyretic action. Greater sensitivity to central alpha-MSH in the older rabbits may account for the reduced febrile response seen in the aged. The findings support previous data which suggest that central alpha-MSH has a physiological role in the limitation of fever.