Metabolism by the rabbit of intravenously administered adenine

A study was made of the metabolism by the rabbit of adenine administered intravenously at a dose of 35 mg/kg with 100 micronCi of 8-14C-adenine. The infused adenine was removed from the blood in two phases, first by diffusion into the tissues and second by metabolic reactions throughout the body. The adenine equilibrated within a few seconds equally between plasma and red blood cells and between them and kidney, liver, duodenum, lung and heart. Diffusion into skeletal muscle was much slower and into brain slowest. The more gradual disappearance of adenine from blood, and from the rest of the body, with a half-life of about 20 minutes and with complete removal by two hours, was predominantly along three pathways, leading to, after four hours: 1) 74 per cent in adenine nucleotide (mostly AMP, ADP, and (ATP); 2) 12 per cent as unchanged adenine in the urine; and 3) 11 per cent as a mixture in almost equal parts of 8-oxyadenine and 2,8-dioxyadenine in the urine. Conversion of adenine to adenine nucleotide, probably by initial reaction with phosphoribosyl pyrophosphate and adenine-phosphoribosyltransferase, was at widely different rates in the organs with duodenum, kidney, liver, and lung high and heart, red blood cell, skeletal muscle and brain relatively low. Sites of formation of the two oxyadenines, probably by action of xanthine oxidase, were not determined.