Journal of Applied Physiology, Vol 50, Issue 5 962-966, Copyright © 1981 by American Physiological Society
Myocardial norepinephrine turnover during induced hypothermia and rewarming
S. B. Jones
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.
