Determination of cyclophosphamide metabolites by gas chromatography and thermionic specific detection : Interindividual differences in hepatic biotransformation of cyclophosphamide in man in vitro

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Enhanced cellular adenosine uptake limits adenosine receptor stimulation in patients with hyperhomocysteinemia.

Contains fulltext : 48279.pdf (publisher's version ) (Open Access)OBJECTIVE: Endogenous adenosine has several cardioprotective effects. We postulate that in patients with hyperhomocysteinemia increased intracellular formation of S-adenosylhomocysteine decreases free intracellular adenosine. Subsequently, facilitated diffusion of extracellular adenosine into cells through dipyridamole-sensitive transporters is enhanced, limiting adenosine receptor stimulation. We tested this hypothesis in patients with classical homocystinuria (n=9, plasma homocysteine 93.1+/-24.7 micromol/L) and matched controls (n=8, homocysteine 9.1+/-1.0). METHODS AND RESULTS: Infusion of adenosine (0.5, 1.5, 5.0, and 15.0 microg/min/dL forearm) into the brachial artery increased forearm blood flow, as measured with venous occlusion plethysmography, to 2.9+/-0.4, 4.3+/-0.5, 5.6+/-1.1, and 9.6+/-2.1 in the patients and to 2.8+/-0.6, 4.4+/-1.0, 9.0+/-1.7, and 17.0+/-3.1 mL/min/dL in controls (P<0.05). However, adenosine-induced vasodilation in the presence of dipyridamole (100 microg/min/dL) was similar in both groups (P=0.9). Additionally, in isolated erythrocytes, adenosine uptake was accelerated by incubation with homocysteine (half-time 6.4+/-0.3 versus 8.1+/-0.5 minutes, P<0.001) associated with increased intracellular formation of S-adenosylhomocysteine (P<0.0001). CONCLUSIONS: In hyperhomocysteinemia, adenosine-induced vasodilation is impaired but is restored by dipyridamole. Accelerated cellular adenosine uptake probably accounts for these observations. These impaired actions of adenosine could well contribute to the cardiovascular complications of hyperhomocysteinemia

Sensitive and selective detection of urinary 1-Nitropyrene metabolites following administration of a single intragastric dose of diesel exhaust particles (SRM 2975) to rats.

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Influence of Aroclor 1254, phenobarbital, beta-naphthoflavone, and ethanol pretreatment on the biotransformation of cyclophosphamide in male and female rats

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In vivo evidence against a role for adenosine in the exercise pressor reflex in humans.

Contains fulltext : 48357.pdf (publisher's version ) (Closed access)The pressor response to exercise is of great importance in both physiology and pathophysiology. Whether endogenous adenosine is a trigger for this reflex remains controversial. Muscle interstitial adenosine concentration can be determined by microdialysis. However, there are indications that local muscle cell damage by the microdialysis probe confounds these measurements in exercising muscle. Therefore, we used the nucleoside uptake inhibitor dipyridamole as pharmacological tool to bypass this confounding. We used microdialysis probes to measure endogenous adenosine in forearm skeletal muscle of healthy volunteers during two cycles of 15 min of intermittent isometric handgripping. During the second contraction, dipyridamole (12 microg.min(-1).dl forearm(-1)) was administered into the brachial artery. Dipyridamole potentiated the exercise-induced increase in dialysate adenosine from 0.30 +/- 0.08 to 0.48 +/- 0.10 micromol/l (n = 9, P < 0.05), but it did not potentiate the exercise-induced increase in blood pressure. A time-control study without dipyridamole revealed no difference in exercise-induced increase in adenosine between both contractions (n = 8). To exclude the possibility that the dipyridamole-induced increase in dialysate adenosine originates from extravasation of increased circulating adenosine, we simultaneously measured adenosine with microdialysis probes in forearm muscle and antecubital vein. In a separate group of nine volunteers, simultaneous intrabrachial infusion of 100 microg.min(-1).dl(-1) dipyridamole and 5 microg.min(-1).dl(-1) adenosine increased dialysate adenosine from the intravenous but not the interstitial probe, indicating preserved endothelial barrier function for adenosine. We conclude that dipyridamole significantly inhibits uptake of interstitial adenosine without affecting the pressor response to exercise, suggesting that interstitial adenosine is not involved in the pressor response to rhythmic isometric exercise

Impact of metformin on endothelial ischemia-reperfusion injury in humans in vivo: a prospective randomized open, blinded-endpoint study

Contains fulltext : 135927.pdf (publisher's version ) (Open Access)INTRODUCTION: Large prospective studies in patients with type 2 diabetes mellitus have demonstrated that metformin treatment improves cardiovascular prognosis, independent of glycemic control. Administration of metformin potently limits infarct size in murine models of myocardial infarction. This study examined, for the first time in humans, whether metformin limits ischemia-reperfusion (IR) injury in vivo using a well-validated forearm model of endothelial IR-injury. METHODS: Twenty-eight healthy volunteers (age 41+/-6 years, 10 male/16 female) were randomized between pretreatment with metformin (500 mg three times a day for 3 days) or no treatment in a Prospective Randomized Open Blinded Endpoint study. Brachial artery flow mediated dilation (FMD) was measured before and after 20 minutes of forearm ischemia and 20 minutes of reperfusion. FMD analysis was performed offline by investigators blinded for the treatment arm. RESULTS: Baseline FMD did not differ between metformin pretreatment and no pretreatment (6.9+/-3.6% and 6.1+/-3.5%, respectively, p = 0.27, n = 26). FMD was significantly lower after forearm IR in both treatment arms (4.4+/-3.3% and 4.3+/-2.8%, respectively, P<0.001 in both conditions). A linear mixed model analysis revealed that metformin treatment did not prevent the decrease in FMD by IR. CONCLUSION: A 3 day treatment with metformin in healthy, middle-aged subjects does not protect against endothelial IR-injury, measured with brachial artery FMD after forearm ischemia. Further studies are needed to clarify what mechanism underlies the cardiovascular benefit of metformin treatment. TRIAL REGISTRATION: ClinicalTrials.gov NCT01610401

Upregulation of ecto-5'-nucleotidase by rosuvastatin increases the vasodilator response to ischemia.

Contains fulltext : 87537.pdf (publisher's version ) (Open Access)3-Hydroxy-3-methyl-glutaryl-coenzyme A reductase inhibitors (statins) are effective in the primary and secondary prevention of cardiovascular events. Although originally developed to improve lipid profile, statins have demonstrated a surplus of beneficial pleiotropic effects, including improved endothelial function, reduced inflammation, and increased tolerance to ischemia-reperfusion injury. In preclinical studies, increased ecto-5'-nucleotidase activity, the key enzyme in extracellular adenosine formation, plays an important role in these effects. Because human data are absent, we explored the effects of rosuvastatin on ecto-5'-nucleotidase activity and the clinical relevance of increased extracellular adenosine during ischemia in humans in vivo. The forearm vasodilator responses to 3 increasing periods of forearm ischemia (2, 5, and 13 minutes) were determined during placebo and caffeine (an adenosine receptor antagonist) infusion into the brachial artery. At the end of an 8-day treatment period with rosuvastatin (20 mg per day), this whole procedure was repeated. During both experiments, ecto-5'-nucleotidase activity was determined. Vasodilator responses are expressed as the percentage increase in forearm blood flow ratio from baseline. Rosuvastatin increased ecto-5'-nucleotidase activity by 49+/-17% and enhanced the vasodilator response after 2, 5, and 13 minutes of ischemia in the absence (146+/-19, 330+/-26, and 987+/-133 to 312+/-77, 566+/-107, and 1533+/-267) but not in the presence of caffeine (98+/-25, 264+/-54, and 727+/-111 versus 95+/-19, 205+/-34, and 530+/-62). Rosuvastatin increases extracellular formation of adenosine in humans in vivo probably by enhancing ecto-5'-nucleotidase activity. This action results in the improvement of reactive hyperemia and may further enhance the clinical benefit of statins, in particular in conditions of ischemia.01 oktober 201

Experimental study of diclofenac and its biliary metabolites on anastomotic healing

Contains fulltext : 195656.pdf (publisher's version ) (Open Access)Background: Diclofenac increases the risk of anastomotic leakage, but the underlying mechanism is unknown. As diclofenac is excreted largely as biliary metabolites, the aim of this study was to determine the effect of these metabolites on intestinal anastomoses. Methods: This was a randomized controlled blinded experiment using 210 male Wistar rats to assess the effect of 'diclofenac bile' on the anastomotic complication score, leak rate and anastomotic strength following oral and parenteral administration of diclofenac. Bile duct and duodenal catheterization techniques were used for diversion and replacement of bile, and biliary diclofenac metabolites were determined. Results: Replacement of control bile with diclofenac bile resulted in higher anastomotic complication scores (P = 0.006) and leakage in five of 18 animals, compared with one of 18 controls (P = 0.089). In turn, following oral diclofenac administration, replacement of diclofenac bile with control bile reduced anastomotic complications (P = 0.016). The leak rate was seven of 15 versus 13 of 17 without replacement (P = 0.127). After intramuscular administration of diclofenac, the reduction in anastomotic complications was not significant when bile was replaced with control bile (P = 0.283), but it was significant when bile was drained without replacement (P = 0.025). Diclofenac metabolites in bile peaked within 2 h after administration. Administration of diclofenac bile resulted in nearly undetectable plasma levels of diclofenac (mean(s.d.) 0.01(0.01) mug/ml) after 120 min. Following oral diclofenac, bile replacement with control bile did not affect the plasma concentration of diclofenac (0.12(0.08) mug/ml versus 0.10(0.05) mug/ml with diclofenac bile; P = 0.869). Conclusion: Altered bile composition as a result of diclofenac administration increases the ileal anastomotic complication rate in rats