Circadian variation in plasma dopamine levels in man.

Nocturnal and daytime recumbent secretory patterns of norepinephrine, epinephrine and dopamine were determined at 30 min intervals in 9 normotensive males. Plasma levels of dopamine as well as those of norepinephrine and epinephrine followed a circadian pattern in these recumbent males. Plasma levels of dopamine were more closely related to clock time (r = -0.54, p less than 0.001) than either norepinephrine or epinephrine levels. As for norepinephrine and epinephrine, the sleep period in all 9 males was characterized by a paucity of dopamine secretory peaks as well as lower mean dopamine levels than during the awake state. There was a strong relationship between the circadian changes in plasma dopamine levels and those of norepinephrine (r = 0.92) and epinephrine (r = 0.78) throughout the 24-h period of recumbency. These interrelationships are consistent with a common regulatory mechanism governing the sleep/wake and/or rest/activity in plasma catecholamine levels.