Circadian variations of free and sulfoconjugated catecholamines in normal subjects.

Normotensive recumbent subjects exhibit an early (11 p.m.) nocturnal increase in plasma dopamine, norepinephrine and epinephrine sulfates. In individual patients, this peak value is followed by a smaller nocturnal peak of catecholamine sulfates, while free catecholamine levels change in a direction opposite to catecholamine sulfates. This reciprocity of changes cannot however be demonstrated in the whole group. The origin of the nocturnal peaks of catecholamine sulfates is unknown. It may be due to a nocturnal decrease of the renal clearance of catecholamine sulfates, an increased generation of sulfates for reasons other than an increase in the free catecholamine substrate, or possibly a release of catecholamine sulfates from the brain.