Diurnal changes in dopamine-beta-hydroxylase, homovanillic acid and 3-methoxy-4-hydroxyphenylglycol in serum of man.

Dopamine-beta-hydroxylase activity (DBH) and concentrations of homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured in serum of 11 normal volunteers at 8 a.m., 2 p.m., 8 p.m. and 2 a.m. DBH was higher at 8 a.m. (p less than 0.05) and lower at 2 a.m. (p less than 0.0025). MHPG followed the same course, while HVA was higher at 8 p.m. (p less than 0.05). The mean values for the eleven volunteers were: DBH 65.8+/-25.8 nanomoles hydroxylated tyramine per ml serum and hour (At substrate concentration 0.05 mM), HVA 89.9+/-57.3 ng/ml serum and MHPG 10.9+/-3.4 ng/ml, with variation coefficient of 38.6, 63.8 and 30.1 respectively. The circadian variations found in serum parallel the data from estimations of MHPG and HVA in urine by other investigators. It is suggested that the diurnal variations of DBH, MHPG and HVA reflect the alternating activity of the catecholaminergic neurons in the peripheral as well as the central nervous system.