Platelet monoamine oxidase B activity changes across 31 days of smoking abstinence.

Although recent studies demonstrate that tobacco cigarette smoke substantially inhibits both central nervous system and blood platelet monoamine oxidase (MAO) activity, little is known about the time course of MAO increases after smoking cessation. Therefore, changes in platelet MAO-B activity and mood were assessed before and at multiple times after quitting smoking. Quitting smoking was associated with a significant (22%) increase in MAO activity by day 3 and with a maximum increase (about 50%) by day 10 that was maintained through day 31 of abstinence. However, abstinence-related increases in depressive mood peaked at day 2 of abstinence, a week more rapidly than the peak increase in MAO-B activity. Neither mood nor MAO-B activity returned to baseline or smoking control levels across the 31-day abstinence period. The asynchrony of increased negative affect and MAO-B activity during the first few days of abstinence may reflect any of several possibilities. First, the duration of the platelet life cycle may not reflect central MAO-B or MAO-A activity. Second, MAO-B may not contribute to or index mood changes during the first days of abstinence though it may contribute to protracted abstinence-induced negative affect. These findings are discussed in terms of the hypothesis that platelet MAO activity reflects central nervous system MAO changes that promote increased depressive affect resulting from smoking abstinence.