Abstract

Repeated immobilization of rats results in a striking increase in adrenal medullary dopamine β-hydroxylase activity. After six periods of immobilization the levels are highest preceding the next immobilization, decrease during the immobilization, and increase upon termination of the immobilization. Six hours after the immobilization the activities return nearly to the preimmobilization levels. Denervation of the adrenal markedly diminishes the increase in dopamine β-hydroxylase activity that occurs with repeated immobilization. Prior treatment with hexamethonium prevents the decrease in activity during the immobilization interval, whereas the protein synthesis inhibitors actinomycin D and cycloheximide prevent the increase in enzyme activity seen after termination of immobilization. These observations support the view that dopamine β-hydroxylase is released as a result of neural stimulationn during immobilization and suggest that its increase following cessation of immobilization is a consequence of accelerated synthesis of the enzyme.