Cellular ATP (adenosine 5’-triphosphate) and its derivatives ADP, AMP and adenosine exert a fundamental role in energy metabolism and enzyme regulation. In the last decades, however, it became evident that extracellular ATP and its derivatives also exert a variety of effects in several cell types including both metabolic and hemodynamic alterations. In the liver, extracellular ATP stimulates glycogenolysis by means of a direct stimulation of glycogen phosphorylase and also in consequence of a stimulation of thromboxane and prostaglandin release by Kupffer cells. ATP and its derivatives also increase oxygen consumption and the potassium flux across the hepatocyte cell membrane and decrease bile flow. Besides these metabolic effects ATP and its derivatives can also affect hemodynamics. Both vasoconstriction and vasodilation have been reported. Most studies about the hemodynamic alterations have been done by measuring pressure changes in perfused organs or in vivo. Though valuable, such measuremens represent an indirect way of assessing volume changes. Recently a few studies have been done in which the multiple-indicator dilution technique was used in the investigation of the hemodynamic action of the purinergic agents. This technique allows to quantify and, in several cases, to localize volume changes. This revision has the following purposes: a) to present a description of the variety of effects of extracellular ATP and other purinergic agents in the liver, b) to emphasize the importance and power of the multiple-indicator dilution technique for studying the action, not only of the purinergic agents, but of any other agent that exerts multiple hemodynamic effects.
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