Modification of the circadian body temperature rhythm of the spontaneously hypertensive rat during and following cessation of continuous clonidine infusion.

The effects of continuous clonidine infusion (10 micrograms/kg/h for 10 days) and the cessation of this infusion on the circadian body temperature rhythm of the spontaneously hypertensive (SH) rat were examined. This circadian rhythm was blunted significantly during the infusion of clonidine. The fall in body temperature which normally occurs at the onset of each light phase was attenuated during the clonidine infusion, and as such, these rats displayed a relative hyperthermia over the light but not the dark phases. On cessation of infusion (24:00 h), a distinct hyperthermia occurred within the immediate dark phase and the subsequent light phase. The results demonstrate that the circadian control of body temperature is disturbed both during and after continuous clonidine infusion.