Mononuclear leukocyte levels of G proteins in depressed patients with bipolar disorder or major depressive disorder.

Stimulatory (Gs) and inhibitory (G(i)) guanine nucleotide binding protein alpha subunit levels were measured in mononuclear leukocytes from 22 drug-free depressed patients (eight with bipolar disorder, 14 with major depressive disorder) and a comparison group of 17 age- and sex-matched healthy subjects. The levels of Gs alpha and G(i) alpha were significantly higher (160% and 114%, respectively) in the bipolar patients, but not the patients with major depressive disorder, than in the healthy subjects. These data add to the evidence for abnormalities in G protein levels and function in the pathophysiology of bipolar disorder.