The effect of lithium on diacylglycerol (DAG), which is an intracellular second messenger, was compared with those of carbamazepine and setiptiline ex vivo through phosphatidylinositol turnover (PI response). Consequently, (1) PI response cycling by stimulation of norepinephrine participated in the alpha 1 receptor. (2) DAG accumulation in rat brain exhibited a biphasic pattern. (3) Lithium elevated DAG accumulation at 30 seconds after stimulation by norepinephrine. (4) Carbamazepine did not affect DAG accumulation. (5) Setiptiline decreased DAG accumulation at 30 minutes after stimulation by norepinephrine.