Changes in serum dopamine-beta-hydroxylase activity during cold pressor test in subjects with high and low basal activity of this enzyme.

Twenty-seven healthy subjects, eight with high levels, eight with low levels and eleven with intermediate levels of serum dopamine-beta-hydroxylase (DBH) activity, were investigated. Serum DBH activity and blood pressure were measured in their response to the cold pressure test (CPT). Plasma renin activity (PRA) was also estimated. Blood pressure, systolic and dyastolic, increased equally in the three groups. PRA did not change significantly throughout the test in any of the groups. Serum DBH activity increased significantly in the group with low initial levels. No significant changes were seen in the controls and in the group with high initial serum DBH activity. It is suggested that subjects with high basal serum DBH activity might have a genetically-determined high sympathetic tone and therefore would hardly respond to a mild stress like CPT; the opposite might be true for the subjects with low basal DBH activity levels.