Platelet monoamine oxidase activity and cigarette smoking.

Platelet MAO activity and plasma thiocyanate concentrations were determined in 72 normal volunteers (22 non-smokers and 50 smokers). Thiocyanate concentrations were used as an index of exposure to cigarette smoke. A significant negative correlation between MAO and thiocyanate concentration was observed for the group (rs = 0.35; P less than 0.005). When examined by sex, the correlation was significant for females but not for males. Mean MAO activity was significantly lower for female smokers than for female non-smokers. For males, no significant differences in MAO activity were observed between smokers and non-smokers. It is possible that smoking causes inhibition of MAO by a direct effect or by indirect effects such as altering hormone levels. Alternatively women with a low MAO activity have a greater innate tendency to smoke.