Antagonism by indomethacin of neurogenic hyperthermia produced by unilateral puncture of the anterior hypothalamic/preoptic region.

1. In unanaesthetized rats, restrained at an ambient temperature of 24 degrees C, the anterior hypothalamic/preoptic (AH/PO) region was lesioned unilaterally by acute mechanical puncture.2. In control (no pre-treatment) rats, unilateral AH/PO puncture produced a neurogenic hyperthermia which began immediately, reached its peak magnitude (mean peak magnitude = +2.3 degrees C) within 60-90 min and persisted usually for 8-16 hr. At defervescence, core temperature fell to a level near that of the pre-lesioning base line.3. The prostaglandin synthesis inhibitor, indomethacin, administered I.P. at doses of 5 and 15 mg/kg 1 hr before puncture of the AH/PO region, attenuated the lesion-induced hyperthermia in a dose dependent fashion. The higher dose reduced peak magnitude by 80% and the 6 hr Fever Index by 88%. The vehicle used to dissolve the indomethacin (60% DMSO/40% saline) did not significantly attenuate the hyperthermia.4. In rats that were hyperthermic after AH/PO damage, indomethacin (10-15 mg/kg I.P.) caused core temperature to fall promptly to near the prelesion base line. Reversal occurred whether the indomethacin was injected while core temperature was still rising or late in the plateau phase of the hyperthermia.5. It is suggested that the neurogenic hyperthermia elicited by unilateral lesioning of the AH/PO region was mediated by prostaglandins released from injured tissue and possibly from extravasated blood. Evidence is cited indicating that the most likely sites of action of the released prostaglandins are the surviving portion of the AH/PO region on the punctured side and the intact contralateral AH/PO region.