beta-Endorphin plasma levels during neuromuscular blockade in unanesthetized cat

Plasma concentrations of beta-endorphin were measured by radioimmunoassay in cats prepared chronically for sleep-waking polygraphic recordings and blood collection. beta-Endorphin (beta-END) levels were found to be stable in baseline conditions and were used as an index of stress. After habituation of each cat to experimental conditions in a veterinary pouch with head restraint, this partial restraint (45 min) or a short-lasting paralysis (30 min) induced by gallamine triethiodide did not significantly elevate plasma concentrations of beta-END. In contrast, hypoxia, ether-induced stress or tight immobilization of the limbs promoted a 7--8-fold increase in beta-END plasma levels. Sleep-waking patterns were not significantly different in restrained and paralyzed conditions. It is concluded that short-lasting paralysis induced in habituated animals by curarizing agents is not accompanied by a significant neuroendocrine response if all possible sources of pain are carefully avoided.