Rat liver Ito cells were cultured for 24 hr with 20% newborn calf serum. Stimulation with the sympathetic neurotransmitter noradrenaline (0.1 mumol/L to 1 mmol/L) led to a dose-dependent increase in prostaglandin F2 alpha release and a slightly smaller enhancement of prostaglandin D2 production. Prostaglandin F2 alpha and prostaglandin D2 synthesis was highest in the first 30 sec after stimulation. Stimulation with the possible cotransmitter ATP (10 mumol/L and 1 mmol/L ATP) also enhanced both prostaglandin F2 alpha and prostaglandin D2 release strongly. The release was highest again during the first 30 sec. Stimulation with noradrenaline and ATP simultaneously did not increase the effects of noradrenaline or ATP alone. Adenosine had no effect on prostaglandin production. The effects of noradrenaline were inhibited specifically by the alpha 1-adrenoreceptor antagonist prazosin but not by the p1-purinoreceptor antagonist 8-phenyltheophylline. The effects of ATP were not antagonized by the inhibitors. Because the metabolic actions of sympathetic hepatic nerves can be inhibited by inhibitors of prostanoid synthesis and mimicked by prostaglandins F2 alpha and D2, and because the Ito cells are well innervated, our results permit the conclusion that Ito cells could be involved in the nervous signal chain: During sympathetic nerve action the neurotransmitter noradrenaline and the cotransmitter ATP cause increases in prostaglandin F2 alpha and prostaglandin D2 release from Ito cells within 30 to 60 sec by way of alpha 1 and p2 receptors, respectively. The released prostaglandins then activate glycogenolysis in the hepatocytes proper.