Vasopressin functions as an endogenous antipyretic in the newborn.

These experiments sought to determine the role of arginine vasopressin (AVP) in the inability of newborns to produce a fever. Our data demonstrate that the AVP analog, [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid)-2-(O-methyl) tyrosine]arginine vasopressin (M-AVP), administered centrally to adult rats, prevented the antipyretic action of centrally injected AVP. Behaviorally thermoregulating 3-day-old rat pups failed to respond to endoxin with a fever, similar to neonates of other species, but when central AVP antipyretic receptors were blocked by pretreatment with M-AVP, the pups were able to raise their body temperature to febrile levels. The antipyretic drug, indomethacin, prevented these fevers. We conclude that endogenous AVP is a physiologically important antipyretic substance in the brain of the newborn rat.