Changes in pre- or postsynaptic adrenergic mechanisms modify the thermoregulatory responses produced by pyrogen in rabbits.

1. Thermoregulatory responses to BHT 920, prazosin (PRA) and 6-hydroxydopamine (6-OHDA) were investigated in pyrogen (lipopolysaccharide Escherichia coli, LPS) treated rabbits. 2. All the compounds in question, despite their different selectivity for pre- or postsynaptic adrenergic structures, significantly reduced pyrogen fever. Antipyresis was associated with inhibition of the metabolic rate. 3. The role of adrenergic mechanisms in fever, with particular respect to those of postsynaptic alpha-2, is discussed.