Plasma levels of total 3-methoxy-4-hydroxyphenylglycol (MHPG) were measured in a group of 104 hospitalized depressed patients and a group of 104 age- and sex-matched normal controls. Plasma MHPG levels were found to be normally distributed in both groups and significantly lower in depressives than in controls. However, this difference could be related to an increase in plasma MHPG levels with age found in controls (r = 0.601, d.f. = 102, p < 0.01) but not in depressives (r = 0.013, d.f. = 102, NS). Men had significantly higher levels than women in both groups. There was no significant difference in plasma MHPG levels among any DSM-III-R diagnostic subgroups of depressives or between patients who were suppressors on the dexamethasone suppression test and those who were nonsuppressors. Significant correlations were found between AMDP Depression Rating Scale item and total scores and levels of plasma MHPG. Age, sex and clinical symptoms appeared to be main sources of variance in studying depressed patients and comparing them with normal controls.

Plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) were found to be significantly higher in manic patients than in age- and sex-matched normal controls (n = 22). In 18 manic patients plasma MHPG correlated with manic symptoms but not with anxiety, depression, motor behaviour, acute psychosis, schizophrenia and severity of illness. A positive correlation between MHPG and grandiosity items on rating scales suggests a link with cognitive contents and therefore a relationship with central factors.

SUMMARYPlasma levels of total 3-methoxy-4-hydroxyphenylglycol (MHPG) were found to be significantly higher in patients with Alzheimer's disease (N=20) than in age-and sex-matched normal controls and dexamethasone-resistant melancholic patients. Contrary to previous studies, the highest levels were not found in the most severely demented patients and this increase was not related to the duration of the illness. Although the significance of these findings remains unclear, they suggest that determination of total plasma MHPG may be useful in the differential diagnosis of Alzheimer's disease and depressive disorder.