Evidence for Inhibition by β-Endorphin of Vasopressin Release during Foot Shock-Induced Stress in the Rat

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Abstract
This study was to ascertain the effect of naloxone and dexamethasone on vasopressin and .beta.-endorphin release in the rat during inescapable electric foot shock stress. Plasma vasopressin concentrations were not affected by electric foot shock in vehicle-treated rats, but were raised significantly by the stress in animals pretreated with naloxone. The stress-induced increase in plasma .beta.-endorphin-like immunoreactivity (.beta.-EI) was similar whether the rats had received naloxone or not. Plasma .beta.-EI consisted of equal amounts of .beta.-endorphin-like and .beta.-lipotropin-like material as revealed by gel filtration. Dexamethasone almost abolished the foot shock-induced increase in plasma .beta.-EI and, in the presence of dexamethasone, stress was now effective in elevating plasma vasopressin concentrations. Evidently, .beta.-endorphin, released from the anterior pituitary, inhibits the release of vasopressin from the posterior lobe of the pituitary gland during foot shock-induced stress.