The circadian variation of catecholamine metabolism in the subhuman primate

Cerebrospinal fluid (CSF) was removed continuously in 2- or 3-h aliquots from the lateral and fourth cerebral ventricles of chronic chair restrained rhesus monkeys. Under conditions of 12 h light (06.00-18.00 h) and 12 h darkness (18.00-06.00 h) the concentrations of norepinephrine (NE) were found to describe a circadian pattern, with maximal concentrations occurring during the light hours and minimal concentrations occurring during the dark hours. The patterns were generally coincident with the circadian patterns of brain temperature and body activity. When assayed for 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) and 3-methoxy-4-hydroxymandelic acid (VMA), samples of CSF collected over 3-4 days demonstrated no reproducible pattern of change. Fluctuation in the concentration of MHPG did not correspond in direction or magnitude to changes in the concentration of VMA. These random fluctuations may in part be accounted for by the influx of the metabolites from peripheral sources to the brain and CSF, and by the relatively slow movement of these metabolites as they diffuse from brain parenchyma to the CSF.