The effect of fever on central alpha-MSH concentrations in the rabbit.

The recent demonstration of the ability of centrally administered alpha-MSH to reduce pyrogen-induced fever in rabbits suggested a role for the peptide in central temperature control. Using a sensitive radioimmunoassay we have established the presence of immunoreactive alpha-MSH (ir alpha-MSH) in discrete CNS sites of the rabbit and have demonstrated a distribution of this activity similar to that seen in other species. Pyrogen-induced fever did not alter concentrations of ir alpha-MSH in tissue extracted from the paraventricular region of the hypothalamus, median eminence, midbrain central grey, preoptic/anterior hypothalamic region, pineal or pituitary. A decrease in arcuate nucleus ir alpha-MSH content was seen in febrile animals, although this change was not statistically significant. Significantly higher levels of ir alpha-MSH were detected in septal extracts of febrile rabbits (0.81/+-0.10 pg/micrograms protein, n=9) than in extracts from afebrile controls (0.54/+-0.04, n=17). This finding suggests the septum to be the central site of action of alpha-MSH to inhibit fever and further implies a modulatory role of the peptide in the central control of thermoregulation.