Afternoon continuous plasma levels of 3-methoxy-4-hydroxyphenylglycol and age. Distinctive biologic subgroups of endogenous depression?

Afternoon continuous plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) were first shown to be a good representation of the mean 24-hour plasma level of MHPG in 18 normal subjects. Then, after the stability of the procedure was tested and retested, the afternoon continuous test for plasma MHPG levels was performed in 57 normal subjects and 42 endogenously depressed patients. A significant correlation between plasma MHPG levels and age was found in normal subjects and depressive patients. When the variable of age was taken into account, a distinct pattern of increasing plasma MHPG levels with age--the "MHPG per age"--was found in the depressed patients, especially the women, who could be divided into high or low MHPG per age groups. There was almost no association between plasma levels of MHPG or MHPG per age values and clinical symptoms, and the two biologic subgroups did not differ clinically.