Demonstration of Endogenous Pyrogen in Afebrile Rabbits

Abstract

A VARIETY of environmental factors, including position, are known to influence temperature regulation in experimental animals. Rectal temperature will fall l°–2° C over a 2-h period in rabbits fastened to a board¹. In addition, securely restrained rabbits in a normal, standing position will develop hypothermia of as much as 2.7° C during a 30–90 min period and exhibit reduced febrile responses to pyrogens when compared to ‘free’ animals². Fekety recently reported a fall in baseline rectal temperatures when rabbits were shorn, restrained supine, or chilled; furthermore, large doses of endotoxin, adrenaline, or endogenous pyrogen failed to elicit fever³. It was postulated that the hypothermia resulted from increased heat loss, since covering the shorn and supine rabbits with blankets restored normal pyrogenic responsiveness³. As some of these differences in febrile reactivity might be due to alterations in the production of endogenous pyrogen, this possibility was investigated.