Plasma catecholamine concentrations in unanesthetized rats during sleep, wakefulness, immobilization and after decapitation.

A relatively unstressful technique for obtaining blood samples from rats has been employed to determine the amounts of catecholamines in blood during physiological sleep, undistrubed wakefulness, gentle handling and physical immobilization. These circulating plasma levels of catecholamines [0.46 ng of norepinephrine (NE) and 0.18 ng of epinephrine (EPI) per ml*were found to be markedly lower than previously reported for rats, which were generally handled or restrained prior to blood sampling. Compared with animals in natural sleep, awake rats had increases in plasma levels of EPI but larger increases of NE. Gentle handling, produced an additional increase in EPI only, whereas physical immobilization, produced massive elevations of circulating levels of both EPI and NE. Decapitation was found to be associated with a 10-fold increase in circulating NE and an 80-fold increase in circulating levels of EPI, whereas dopamine remained at undetectable levels. The high levels of plasma catecholamines in rats compared with other animals and humans, and changes produced in pharmacological and physiological experiments, probably reflect environmentally induced changes in sympathoadrenomedullary activity rather than differences in basal sympathetic neuronal activity.