Prolactin levels increased by physical exercise correlate with platelet monoamine oxidase activity: Evidence linking platelet MAO with serotonin release capacity

Objective: Lower platelet monoamine oxidase (MAO) activity has consistently been associated with excessive risktaking and general psychiatric vulnerability. How this peripheral measure can represent presumably centrally regulated complex behaviours is not clear but platelet MAO activity has been suggested to reflect the capacity of serotonin release in the brain. Secretion of prolactin is in part under serotonergic control and indicates serotonin release capacity. Methods: We have assessed release of prolactin and other exercise-induced hormones in response to strenuous physical exercise in twenty male subjects and examined its association with platelet MAO activity as measured radioenzymatically. Results: Increase in prolactin levels was positively correlated with platelet MAO activity. Levels of cortisol, growth hormone and aldosterone were also raised by exercise, but these increases were not associated with platelet MAO activity. Unexpectedly, aldosterone levels before exercise were also in a positive correlation with platelet MAO activity. Conclusion: The finding that exercise-induced prolactin release is associated with MAO activity in platelets indirectly supports the notion that platelet MAO activity is a marker of central serotonin release capacity.