Biphasic effects of smoking on human serum dopamine-beta-hydroxylase activity.

To investigate the chronic effects of smoking on sympathetic nerve activity, serum dopamine-beta-hydroxylase (DBH) activity was determined in 119 male non-smokers and 183 age-matched male smokers. The smokers were classified into 3 groups: 51 light smokers (1-19 cigarettes/day), 76 moderate smokers (20 cigarettes/day), and 56 heavy smokers (more than 20 cigarettes/day). The light smokers had the highest mean DBH activity, and the heavy smokers had the lowest mean DBH activity in the 4 groups. These results suggest that light smoking stimulates the sympathetic nervous system, but that heavy smoking depresses the system. These biphasic changes in DBH activity are similar to the pharmacological effects of nicotine on the peripheral sympathetic nervous system.