CHANGE IN PLATELET GTP-BINDING PROTEIN IN DRUG-FREE DEPRESSED-PATIENTS

In order to examine the status of cell signal transduction in depressi on, we measured in the same subjects both the platelet guanine nucleot ide binding protein (G protein) levels and G protein function in drug- free depressed patients. G protein levels were measured thanks to the method of Western immunoblot of three G protein subunits, i.e. G alpha i(2); G alpha q and G beta. The G protein function was assessed by th e method of GTP gamma S binding through platelet alpha 2-adrenoceptor stimulation. The results showed an increase in immunoreactivity of the three G proteins in major depressed patients. The study of GTP gamma S binding on platelet membrane showed a significant decrease in drug-f ree depressed patients with respect to age- and gender-matched control s. These data suggest that uncoupling of alpha 2-adrenoceptor from G p roteins, whose levels were increased, may be found in depression.