Abstract
Previous work has shown considerable purine (mostly uric acid) production by isolated guinea-pig ileum preparations used in studies of adenosine receptor pharmacology. This tissue was stimulated at 0.2Hz and the purine efflux studied by HPLC. The following drugs were added to the medium (alone or in combination) 20 min before the study and were present throughout the study: deoxycoformycin (dCF, 10μM), 6-(2hydroxy-5-nitrobenzylthioguanosine (HNBTGR, 1μM) allopurinol (10μM and 50μM) and oxipurinol (10μM). Allopurinol and oxipurinol increased the proportion of hypoxanthine and xanthine and did not reduce purine efflux, but this was reduced when dCF and/or HNBTGR was present. The results show about one quarter of the uric acid is preformed and the rest synthesised via adenosine in the course of the experiment, in both the tissue and the medium. Since endogenous purine concentrations are in excess of the I.C.50 of adenosine in this tissue they are an important consideration in the interpretation of experiments with exogenous purines and purine analogs.
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