Further characterization of the inhibition of platelet aggregation by a plasma factor(s) in unmedicated unipolar depressed patients.

To investigate further the inhibition of platelet aggregation by a plasma factor(s) in unipolar depression, a series of assays were performed in which the platelet-rich plasma of a male volunteer was preincubated with the plasma of either unmedicated unipolar depressed patients or age-matched controls. Platelet aggregation was initiated by the following aggregating agents; ADP (10 and 2.5 microM), ADP/5HT (0.5 microM ADP + 50 microM 5HT and 0.5 microM ADP + 25 microM 5HT) and adrenaline (10 and 1 microM) (that act on different platelet membrane receptors) and by the following agents; sodium fluoride (20 mM), calcium ionophore A23,187 (19 microM) and phorbol-12-myristate-13-acetate (3.24 microM) (that act at specific intracellular sites). The plasma of depressed patients significantly reduced the platelet aggregatory response for each of the aggregating agents at each of the concentrations tested. Therefore, it is concluded that the inhibition of platelet aggregation by a plasma factor(s) may be irreversible in nature and may have an intracellular site(s) of action, possibly at, or beyond, the site of activated protein kinase C.