Synthesis of adrenal catecholamines in rats during and after immobilization stress.

Repeated intervals of immobilization previously have been found to cause elevation of levels of tyrosine hydroxylase in the adrenals of rats. In the present study it was found that the increased levels of enzymes result in enhanced synthesis of epinephrine-14C from tyrosine-14C but not from dopa-3H. During immobilization, conversion of tyrosine-14C to catecholamines is further increased and may exceed the capacity of even the elevated levels of dopa- mine-β-hydroxylase to convert dopamine to nor-epinephrine. Thus, while tyrosine hydroxylase is normally rate limiting, dopamine-β-hydroxylation may become rate limiting when dopamine formation is markedly accelerated. (Endocrinology 89: 46, 1971)