Effect of handling and forced immobilization on rat plasma levels of epinephrine, norepinephrine, and dopamine-beta-hydroxylase.

Forced immobilization of rats triggers activation of adrenal-medullary discharge of epinephrine (EPI) and sympathetic neuronal release of norepinephrine (NE). Plasma levels of EPI reach peak values, which are about 40-fold greater than in undisturbed rats, at about 20 min and then decline to about one-third the peak levels. Plasma levels of NE are increased about 6-fold throughout the immobilization interval. Decapitation produces an 80-fold increase in plasma levels of EPI and an 8-fold increase in NE. These striking decapitation-induced increases are potentiated about 3-fold by immobilization, presumably as a consequence of an immobilization-induced alteration in the "set" of responsivity of spinal cord mechanisms controlling sympathoadrenal medullary discharge. Even minor disturbances produce highly significant increases in plasma EPI and NE and special precautions must be observed when studies involving plasma catecholamines or their effects are performed in animals.