Calorigenic response of burned rats with adrenal medullectomies to catecholamines

In previous studies, we established that circulating epinephrine (E) is not essential for a normal hypermetabolic response to burn injury in the rat, within the zone of thermal neutrality. In other studies, burned rats with adrenal medullectomy (AdxB) studied at 22 degrees C were unable to maintain rectal temperature (TR) after alpha-adrenergic blockage. These data suggest that norepinephrine (NE) is calorigenic in such animals without formal cold acclimation. These studies investigate the hypothesis that, contrary to the usual belief, norepinephrine might be calorigenic in rats without formal cold acclimation. Burned (B) and control (C) rats with adrenal medullectomies (Adx) and Sham (S) Adx (AdxB, SAdxB, AdxC, and SAdxC) were housed at either 22 degrees C or 28 degrees C. Calorimetry was performed during the eighth to eleventh days after the burn. For groups housed at 22 degrees C and studied at 28 degrees C, NE given intravenously (iv) produced an average 16.5%+/-3.3% increment in heat production (HP) for the four groups, which was significant for AdxB, SAdxB, and SAdxC. Intravenous administration of E produced an average increment in HP of 4.44%+/-4.1%, which was not significant. HP was significantly higher after NE than E in three cases. Studies with animals housed at 28 degrees C and studied at 28 degrees C produced intermediate but similar results. For groups housed at 28 degrees C and studied at 22 degrees C, iv administration of E and NE produced average decreases in He of 18%+/-6.7% for E and 10.75%+/-4.7% for NE. Except for the AdxC group, these differences were significant. These data suggest that chronic exposure to an ambient temperature of 22 degrees C produces an enhanced calorigenic response to NE in burn and control rats. Based on the data presented here, combined with earlier studies, NE must be considered as a facilitator for hypermetabolic response to burn injury in the rat. It is interesting to speculate whether NE is calorigenic for patients with large burn wounds, which are managed without dressings at ambient temperatures below thermal neutrality.