Endogenous levels of catecholamines in the rat myocardium following exposure to stress.

Following exposure of male rats to irregular signalled footshock from which they could escape, the endogenous level of norepinephrine in the myocardium was significantly reduced. In atria the depletion of endogenous norepinephrine was significant following 1 day of stress. This significant depletion was maintained following 4 days of stress but began to return towards control levels by Day 10. A similar, but less pronounced pattern was seen with the ventricles. Little if any epinephrine was detected in both control and stress atria and ventricles. From the results presented it is postulated that irregular signalled footshock results in an inhibition of neuronal uptake.