ROLE OF ALPHA-ADRENOCEPTORS IN THE MAINTENANCE OF CORE TEMPERATURE INHUMANS

1. Although alpha-adrenoceptor antagonists have been shown to induce c ore hypothermia in animals, it is unclear whether the primary mechanis m is increased heat loss or decreased heat production. Furthermore, st udies have not been performed in humans to determine the role of alpha -adrenoceptors in the maintenance of core temperature. 2. alpha-Adreno ceptor blockade was achieved with three doses of phentolamine given by random assignment on three different study days in five male and five female healthy subjects. Core temperature, mean skin-surface temperat ure, fingertip capillary blood flow and metabolic heat production were measured, Dose-response curves were plotted for all measured variable s, and males and females were compared to identify potential gender di fferences. 3. Core temperature decreased with all doses of phentolamin e. At the completion of the phentolamine infusion, the decrease in cor e temperature was more significant with high-dose (0.3 +/- 0.1 degrees C, P = 0.03) and with medium-dose (0.2 +/- 0.0 degrees C, P = 0.05) p hentolamine than with low-dose phentolamine (0.1 +/- 0.0 degrees C). T he maximum core temperature decrease during the study was more signifi cant with high dose (0.6 +/- 1 degrees C) than with medium (0.3 +/- 1 degrees C, P = 0.04) or low (0.3 +/- 1 degrees C, P = 0.005) doses. Me an skin-surface temperature was increased with all doses. Fingertip bl ood flow was increased (approximately 60% above baseline) with the med ium and high doses, but was unchanged with the low dose. Total body ox ygen consumption was unchanged regardless of dose. Although females ha d a higher core temperature at baseline, changes in core temperature, skin-surface temperature and fingertip blood flow were similar in male s and females. 4. These findings suggest that alpha-adrenergicantagoni st-induced hypothermia results from a dose-dependent redistribution of heat from the core to the periphery, and not from a decrease in metab olic heat production. This beads us to conclude that baseline alpha-ad renergic 'tone' serves to maintain core temperature by constraining he at to the core thermal compartment.