title: Myocardial norepinephrine turnover during induced hypothermia and rewarming.
abstract: Norepinephrine (NE) turnover in myocardial tissue was measured in male golden hamsters (Mesocricetus auratus) during 1) continuous hypothermia, 2) rewarming from hypothermia initiated by exposure to 22 degrees C ambient, and 3) normothermic control state. Hypothermia was induced by exposure to 80% He-20% O2 atmosphere at 0 to -10 degrees C. At sequential periods after tritiated norepinephrine ([3H]NE) infusion, hamsters were killed by cervical transection and hearts were removed and analyzed for NE and [3H]NE content. Rate constants, turnover times, and turnover rates were determined from regression analysis of [3H]NE/micrograms NE tissue decay. Myocardial concentrations of NE were constant during NE-turnover measurements in each group. However, myocardial NE levels were reduced by 37% in both continuous hypothermia and rewarming from hypothermia compared with normothermic controls. NE turnover was highest during rewarming from hypothermia (0.34 micrograms.g-1.h-1), but no decay in myocardial [3H]NE was detectable during continuous hypothermia. Control animals had turnover values of 0.15 micrograms.g-1.h-1. Turnover data indicate severe depression in myocardial sympathetic nerve activity during hypothermia but a significant increase above normothermic control levels during rewarming from hypothermia.
mesh_terms: D000320:Adrenergic Fibers / Q000378:metabolism; D000818:Animals; D001831:Body Temperature; D006224:Cricetinae; D006321:Heart / Q000294:innervation; D006605:Hibernation; D008297:Male; D008647:Mesocricetus; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*
chemical_list: D009638:Norepinephrine