Presence of adenosine in the human term placenta. Determination of adenosine content and pathways of adenosine metabolism.

Adenosine, inosine, and hypoxanthine were isolated from human term placentas by paper chromatography of the diaJyzates of aqueous placental homogenates and quantified by ultraviolet spectroscopy. Placentas obtained upon vaginal delivery contained 230 ± 18 nmoles adenosine/g tissue, 300 ± 29 nmoles inosine/g, and 250 ± 19 nmoles hypoxanthine/g. Three prelabor placentas obtained by cesarean section contained 44 =t 3 nmoles inosine/g and 277 ± 22 nmoles hypoxanthine/g, but adenosine was not detected in two of the placentas and was present only at 4 nmoles/g in the third. The activities of placental enzymes catabolizing ATP were determined in homogenates of term placentas. No adenylate deaminase or xanthine oxidase activity was found. Adenosinetriphosphatase, adenylate kinase, and 5'-nucleotidase were more active than were adenosine kinase, adenosine deaminase, and purine nucleoside phosphorylase. The results indicate that in the placenta both the formation of adenosine from adenosine monophosphate and the fate of adenosine, i.e., salvage or catabolism, are influenced by the level of adenosine triphosphate. Possibly, during labor, placental ischemia favors the enzymatic production of adenosine.