Topic
Xanthine
About: Xanthine is a research topic. Over the lifetime, 4046 publications have been published within this topic receiving 129820 citations. The topic is also known as: Xanthine.
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TL;DR: Direct evidence is provided for the clearance of hydroxylated purines and the release of utilizable adenine derivatives by liver and for the export of utilisable purine from liver perfused with oxypurine.
Abstract: We have analyzed for purine compounds entering and leaving the liver in lightly anesthetized rabbits and rats and for the export of utilizable purine from liver perfused with oxypurine. The in vivo results indicate that roughly 80% of hypoxanthine, xanthine, and urate is removed in a single passage of blood through liver. Conversely, the adenosine concentration of hepatic venous blood is increased 10-fold over portal or arterial levels. When the liver is isolated and perfused with hypoxanthine there is significant release of adenosine, whether measured quantitatively by microbiological assay or qualitatively by analysis of the radioactive purines released from liver that has been prelabeled with [14C]hypoxanthine. These results provide direct evidence for the clearance of hydroxylated purines and the release of utilizable adenine derivatives by liver.
61 citations
TL;DR: Evidence is presented that t-butanol serves as a substrate for rat liver microsomes and that it is oxidatively demethylated to yield formaldehyde, and results indicate that t -butanol cannot be used to distinguish metabolically-linked from non-metabolically- linked actions of ethanol.
61 citations
TL;DR: The results indicate that oxygen free radicals may reduce the number of Ca2-channels in the cell membrane and this change may contribute towards decreasing the voltage-dependent Ca2+ influx in the cardiac cell.
61 citations
TL;DR: In a study of purine alkaloid catabolism pathways in coffee,14C-labelled theobromine, caffeine, theophylline and xanthine were incubated with leaves of Coffeeea arabica and the identity of 7-methylxanthine in these studies was confirmed by gas chromatography-mass spectrometry analysis.
Abstract: In a study of purine alkaloid catabolism pathways in coffee,14C-labelled theobromine, caffeine, theophylline and xanthine were incubated with leaves ofCoffea arabica. Incorporation of label into14CO2 was determined and methanol-soluble metabolites were analysed by high-performance liquid chromatography-radiocounting. The data obtained demonstrate catabolism of caffeine → theophylline → 3-methylxanthine → xanthine. Xanthine is degraded further by the conventional purine catabolism pathway to CO2 and NH3 via uric acid, allantoin and allantoic acid. The conversion of caffeine to theophylline is the rate-limiting step in purine alkaloid catabolism and provides a ready explanation for the high concentration of endogenous caffeine found inC. arabica leaves. Although theobromine is converted primarily to caffeine, a small portion of the theobromine pool appears to be degraded to xanthine by a caffeine-independent pathway. In addition to being broken down to CO2, via the purine catabolism pathway, xanthine is metabolised to 7-methylxanthine. Metabolism of [2-14C]xanthine byC. arabica leaves in the presence of 5 mM allopurinol results in very large increases in incorporation of radioactivity into 7-methylxanthine as degradation of the substrate via the purine catabolism pathway is blocked. The identity of 7-methylxanthine in these studies was confirmed by gas chromatography-mass spectrometry analysis.
61 citations
Journal Article•
TL;DR: The results suggest that the increased XO activity detected following TPA treatment is the consequence of TPA-induced XD synthesis, and a conversion of existing and newly synthesized XD to XO.
Abstract: Both xanthine dehydrogenase (XD) and xanthine oxidase (XO) catalyze the conversion of hypoxanthine to xanthine, and xanthine to uric acid. Topical application of a promoting dose of 12- O -tetradecanoylphorbol-13-acetate (TPA) to the dorsal skin of female SENCAR mice resulted in a 3.0–3.5-fold elevation of epidermal XO specific activity. Epidermal XO specific activity was maximally elevated 48–96 h after TPA treatment, and required 11 days to return to control levels. Although TPA increased the XO/(XD + XO) ratio from 0.45 to 0.7, the conversion of preexisting XD to XO could not solely account for the TPA-dependent elevation in XO specific activity since control XD plus XO activity was less than just the XO activity in TPA-treated epidermis. Topical application of cycloheximide simultaneously with, or 12 h after, TPA treatment inhibited the TPA-dependent increases in the XO/(XD + XO) ratio and XO specific activities. Collectively, these results suggest that the increased XO activity detected following TPA treatment is the consequence of TPA-induced XD synthesis, and a conversion of existing and newly synthesized XD to XO. In addition, the in vivo promoting activities of analogues of TPA could be correlated with their abilities to elevate XO activity (TPA > phorbol-12,13-dibenzoate ≫ 4- O -methyl-TPA = phorbol).
61 citations