Effects of the liver on circulating adenosine in blood

The effects of the liver on circulating adenosine in vivo were examined by monitoring plasma adenosine levels in hepatic afferent and efferent blood during intraportal venous (i.p.v.) and intravenous (i.v.) infusions of adenosine (0.04-1 mg.kg-1.min-1). Dilazep, a blocker of nucleoside uptake, was also used for studying the uptake of adenosine into the liver and extrahepatic sites. Basal levels of plasma adenosine in portal venous, arterial, and hepatic venous blood were similar. However, increased adenosine levels during infusions were significantly cleared by a single passage through the liver, suggesting that the liver is a potent organ for eliminating the increased adenosine in circulation. Dilazep inhibits extrahepatic elimination but does not affect hepatic extraction of circulating adenosine. Subtypes of nucleoside uptake are suggested to exist between the liver and other cell types, such as red blood cells.