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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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Journal ArticleDOI
TL;DR: Data indicate that adrenergic receptors in the sarcolemmal membranes are modified by oxygen free radicals.
Abstract: To examine the effects of oxygen free radicals on alpha- and beta-adrenergic receptors, rat heart crude membranes were incubated with xanthine plus xanthine oxidase, H2O2, or H2O2 plus Fe2+. The assay of beta-adrenergic receptors involving [3H]dihydroalprenolol (DHA) binding revealed that the maximal number of binding sites (Bmax) and dissociation constant (Kd) were increased by xanthine plus xanthine oxidase. H2O2 increased the Kd value for [3H]DHA binding. When a hydrophilic ligand, [3H]CGP-12177, was used for the beta-adrenergic receptor assay, an increase in Kd value without any changes in Bmax value was evident on treating the membranes with xanthine plus xanthine oxidase. The assay of alpha-adrenergic receptors involving [3H]prazosin binding showed a decrease in the number of binding sites and an increase in Kd value only after a prolonged period of incubation. Both H2O2 and H2O2 plus Fe2+ increased the Kd value for [3H]prazosin without changes in Bmax. Changes in both alpha- and beta-adrenergic receptors similar to those with crude membranes were also seen by employing the purified heart sarcolemmal membranes. These data indicate that adrenergic receptors in the sarcolemmal membranes are modified by oxygen free radicals.

44 citations

01 Jan 1979
TL;DR: Clear conclusions are led on the optimum timing and dosage of theophylline, and on the need to monitor plasma levels of both theophyelline and caffeine in newborn infants treated with theophyLLine.

44 citations

Journal ArticleDOI
TL;DR: There is species dependency in the myocardial activity of xanthine oxidase or dehydrogenase, that when present it can be inhibited by acute allopurinol pretreatment, and that xanthin oxidase activity and its ability to generate oxygen radicals are not universal contributors to cardiac ischemic damage.
Abstract: Allopurinol is thought to protect hearts against damage due to hypoxia or ischemia by inhibiting xanthine oxidase and oxygen radical generation. We subjected isolated rabbit hearts, equilibrated by perfusion at 37 degrees C, to 1 h of global ischemia at 27 or 37 degrees C with or without brief pretreatment with 100 microM allopurinol. The total absence of xanthine or uric acid in the coronary effluent following ischemia, the presence of hypoxanthine (25 +/- 4 microM peak concentration), and the failure of allopurinol to alter purine washout profiles or postischemic cardiac function suggest that rabbit myocardium lacks xanthine oxidase or dehydrogenase. Data obtained with a similar rat heart preparation showed appreciable formation of xanthine (12 +/- 2 microM peak) and uric acid (10 +/- 3 microM). Allopurinol pretreatment inhibited xanthine and uric acid formation and significantly improved key indicators of postischemic left ventricular function. We conclude that there is species dependency in the myocardial activity of xanthine oxidase or dehydrogenase, that when present it can be inhibited by acute allopurinol pretreatment, and that xanthine oxidase activity and its ability to generate oxygen radicals are not universal contributors to cardiac ischemic damage.

44 citations

Journal ArticleDOI
TL;DR: The results show that the intestinal metabolism of dietary adenine is uniquely different from that of guanine, hypoxanthine or xanthine.
Abstract: One experiment was conducted in which radioactively labeled purine bases (adenine, guanine, hypoxanthine and xanthine) were individually given intravenously to young adult rats and the recovery of radioactivity in urine and gut, gut content and liver was measured at the end of the next 24 hours. The total recovery of radioactivity from orally and intravenously administered adenine was measured in experiment 2. A third experiment measured the recoveries of radioactivity from oral and intravenous adenine in a wider variety of tissues and organs than in experiment 1. The chemical identities of the urinary end products of the metabolism or orally and intravenously administered adenine were compared in a fourth experiment. When purines were given intravenously, significantly more of the administered radioactivity was recovered in urine from rats given guanine, hypoxanthine or xanthine compared with those given adenine. The greater recoveries of radioactivity in urine were associated with smaller recoveries in tissues. A larger proportion of intravenously compared to orally administered radioactivity from adenine was incorporated into all body tissues, and this was most pronounced in glandular and lymphoid tissues. The primary urinary end product of both orally and intravenously administered adenine was allantoin. The absorption of individual purines from isolated rat gut sacs was evaluated in a fifth experiment. A significant proportion of unaltered adenine crossed the mucosal to serosal barrier of intestinal sacs whereas unaltered guanine, hypoxanthine or xanthine did not cross into the serosal fluid. These results show that the intestinal metabolism of dietary adenine is uniquely different from that of guanine, hypoxanthine or xanthine.

44 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202361
2022108
202157
202060
201961
201869