Elevation of serum dopamine-beta-hydroxylase activity with forced immobilization.

Abstract

THE formation of the neurotransmitter noradrenaline from 3,4-dihydroxyphenylethylamine (dopamine) is catalysed by the enzyme dopamine-β-hydroxylase (DBH)1. This enzyme is associated both with the catecholamine-containing chromaffin granules in the adrenal medulla2,3 and with the vesicular structures in sympathetic nerve terminals which contain catecholamines4. Furthermore, DBH activity is released with catecholamines into the perfusate after stimulation of either the isolated perfused adrenal gland5 or the isolated perfused spleen6–8. DBH activity has been reported in the serum of both man and the rat9,10. This activity is similar to adrenal and sympathetic nerve DBH activity with regard to cofactor requirements, oxygen requirement and kinetic characteristics9,10. It has been suggested that serum DBH activity might be present as a result of release of enzyme with catecholamines from the adrenal glands and sympathetic nerves. If this is the case, serum DBH activity might be a useful and convenient index of sympathetic-adrenal activity. The work described here was undertaken to investigate both the source of the serum DBH and the effect on this activity of forced immobilization, a procedure which has been used as a model of stress and which has been shown to release catecholamines from the adrenal gland and increase catecholamine excretion11.