Enzymuria in Streptozotocin-Diabetic Rats

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Diverse inhibitors of de novo purine synthesis promote AICAR-induced AMPK activation and glucose uptake in L6 myotubes

Methotrexate, an immunosuppressant and anticancer drug, promotes glucose uptake and lipid oxidation in skeletal muscle via activation of AMP-activated protein kinase (AMPK). Methotrexate promotes AMPK activation by inhibiting 5-aminoimidazole-4-carboxamide ribonucleotide (ZMP) formyltransferase/inosine monophosphate (IMP) cyclohydrolase (ATIC), which converts ZMP, an endogenous purine precursor and an active form of the pharmacological AMPK activator AICAR, to IMP during de novo purine synthesis. In addition to methotrexate, inhibition of purine synthesis underpins the therapeutic effects of a number of commonly used immunosuppressive, anticancer, and antimicrobial drugs, raising the question of whether activation of AMPK in skeletal muscle could be a recurrent feature of these drugs. Using L6 myotubes, we found that AICAR-induced AMPK activation and glucose uptake were enhanced by inhibitors of the conversion of IMP to GMP (mycophenolate mofetil) or of IMP to AMP (alanosine) as well as by indirect inhibitors of human (trimetrexate) and bacterial ATIC (sulfamethoxazole). 6-Mercaptopurine, which inhibits the conversion of IMP to GMP and AMP, activated AMPK, increased glucose uptake, and suppressed insulin signaling, but did not enhance the effect of AICAR. As determined by measuring oxygen consumption rate, none of these agents suppressed mitochondrial function. Overall, our results indicate that IMP metabolism is a gateway for the modulation of AMPK and its metabolic effects in skeletal muscle cells

Inhaled furosemide for relief of air hunger versus sense of breathing effort: a randomized controlled trial

Background. Inhaled furosemide offers a potentially novel treatment for dyspnoea, which may reflect modulation of pulmonary stretch receptor feedback to the brain. Specificity of relief is unclear because different neural pathways may account for different components of clinical dyspnoea. Our objective was to evaluate if inhaled furosemide relieves the air hunger component (uncomfortable urge to breathe) but not the sense of breathing work/effort of dyspnoea. Methods. A randomised, double blind, placebo-controlled crossover trial in 16 healthy volunteers studied in a university research laboratory. Each participant received 3 mist inhalations (either 40 mg furosemide or 4 ml saline) separated by 30–60 min on 2 test days. Each participant was randomised to mist order ‘furosemide-saline-furosemide’ (n- = 8) or ‘saline-furosemide-saline’ (n = 8) on both days. One day involved hypercapnic air hunger tests (mean ± SD PCO2 = 50 ± 3.7 mmHg; constrained ventilation = 9 ± 1.5 L/min), the other involved work/effort tests with targeted ventilation (17 ± 3.1 L/min) and external resistive load (20cmH2O/L/s). Primary outcome was ratings of air hunger or work/effort every 15 s on a visual analogue scale. During saline inhalations, 1.5 mg furosemide was infused intravenously to match the expected systemic absorption from the lungs when furosemide is inhaled. Corresponding infusions of saline during furosemide inhalations maintained procedural blinding. Average visual analogue scale ratings (%full scale) during the last minute of air hunger or work/effort stimuli were analysed using Linear Mixed Methods. Results. Data from all 16 participants were analysed. Inhaled furosemide relative to inhaled saline significantly improved visual analogues scale ratings of air hunger (Least Squares Mean ± SE − 9.7 ± 2%; p = 0.0015) but not work/effort (+ 1.6 ± 2%; p = 0.903). There were no significant adverse events. Conclusions. Inhaled furosemide was effective at relieving laboratory induced air hunger but not work/effort in healthy adults; this is consistent with the notion that modulation of pulmonary stretch receptor feedback by inhaled furosemide leads to dyspnoea relief that is specific to air hunger, the most unpleasant quality of dyspnoea

Enzymuria of the Rat: The Preparation of Urine for Enzyme Analysis

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