Platelet 5-HT and plasma MHPG levels in patients with bipolar I and bipolar II depressions and normal controls

Background: It has been suggested that platelet serotonin (5-HT) content ma y reflect aspects of the presynaptic reuptake of 5-HT, while plasma 3-metho xy-4-hydroxy-phenylglycol (MHPG) levels may provide an index of central nor adrenergic function. Methods: In order to determine if there is a biologica l distinction in 5-HT or noradrenergic function within bipolar I and bipola r II depressions, we measured levels of platelet 5-HT and plasma MHPG in 12 patients with bipolar I depression, 12 patients with bipolar II depression , and 20 normal healthy controls. All subjects were medication free for at least 4 weeks prior to the study. Results: There was a trend towards higher platelet 5-HT in bipolar I or II depressions when compared to normal contr ols, whereas there was no difference in platelet 5-HT levels between bipola r I and II depressed patients. When bipolar I and II patients were pooled, there was a significant increase in platelet 5-HT levels in bipolar depress ives compared to normal controls, and there was a trend towards a weak posi tive correlation between platelet 5-HT and al-item HAMD scores in the patie nt group. In contrast, there was no difference in plasma MHPG levels betwee n the three groups. Limitations: This study was limited to a small sample s ize, single point sampling and did not match seasons. Conclusions: Our find ings did not provide supportive evidence for a distinctive 5-HT or noradren ergic function within bipolar I and bipolar II depressions. However, the fi nding of increased platelet 5-HT levels in bipolar depressed patients compa red to normal controls is consistent with the results of previous studies, and may suggest an increase in presynaptic 5-HT reuptake, presumably result ing from diminished synaptic 5-HT availability in this condition. (C) 1999 Elsevier Science B.V. All rights reserved.