Dopamine-β-hydroxylase activity in plasma obtained from the pulmonary artery and left ventricle of man

Dopamine-β-hydroxylase activity (DBH) has been measured in plasma obtained simultaneously from the pulmonary artery and left ventricle of fourteen patients who underwent diagnostic cardiac catheterisation. In the majority of these subjects the levels of enzyme activity in the arterial and venous blood were similar, indicating that inactivation of DBH had not occurred in its passage through the pulmonary circulation. One patient with pulmonary hypertension had a large a-v difference in enzyme activity that may have been caused by altered pulmonary haemodynamics. Three of the five subjects that undertook a standardised exercise test on a bicycle ergometer showed a significant increase in plasma DBH activity. There was no correlation between the increases in DBH activity and in cardiac index and heart rate.