Antipyretic effect of arginine vasotocin in toads

Arginine vasotocin (AVT) is a nonmammalian analog of the mammalian hormone arginine vasopressin (AVP). These peptides are known for their antidiuretic and pressor effects. More recently, AVP has been recognized as an importan t antipyretic molecule in mammals. However, no information exists about the role of AVT in febrile ectotherms. We tested the hypothesis that AVT is an antipyretic molecule in the toad Bufo paracnemis. Toads equipped with a te mperature probe were placed in a thermal gradient, and preferred body tempe rature was recorded continuously. A behavioral fever was observed after lip opolysaccharide (LPS) was injected systemically (200 mu g/kg). Systemically injected AVT (300 pmol/kg) alone caused no significant change in body temp erature, but abolished LPS-induced fever. Moreover, a smaller dose of AVT ( 10 pmol/kg), which did not affect LPS-induced fever when injected periphera lly, abolished fever when injected intracerebroventricularly. We therefore conclude that AVT plays an antipyretic role in the central nervous system, by means of behavior, in an ectotherm, a fact consistent with the notion th at AVT/AVP elicits antipyresis by reducing the thermoregulatory set point.