The effect of α-MSH on fever caused by Staphylococcus aureus cell walls in rabbits

The role of endogenous pyrogens induced by gram-positive bacterial pyrogens is not known. Intravenous α-MSH (2.5 μg) significantly reduced only the first phase of the biphasic thermal response to IV S. aureus cell walls (5 × 10 7). Intracerebroventricular α-MSH (200 ng) had no effect on the fever response. The fall in serum iron concentration was significantly attenuated by the IV α-MSH but was not affected by the ICV α-MSH. Intravenous α-MSH had no effect on fever or the serum iron response caused by muramyl dipeptide (MDP). We conclude that the first phase of the thermal response to S. aureus cell walls is mediated by an endogenous pyrogen (EP) and the second phase of the response by a mechanism not involving EP, but possibly a muramyl peptide.