Omar Shaheen

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We review the role of glutathione (GSH) and its metabolizing enzymes, glutathione S-transferase (GST) and glutathione reductase (GSR) in drug metabolism and in the elimination of foreign compounds. Levels of GSH and the activity of these enzymes may be greatly influenced by drugs and other substances in the body. We therefore determined GSH levels and the(More)
Caffeine and theophylline block the vasodilating effects of adenosine and may act to enhance sympathoadrenal discharge and activate the renin-angiotensin system. To determine if these methylxanthines might thereby have effects on regional blood flow, we studied the influence of caffeine and theophylline on apparent liver plasma flow (LPF) in normal subjects(More)
The activities of glutathione-S-transferase (GST) and glutathione reductase (GSR) in mouse lymphocytes as a function of cell concentration and age were determined. Lymphocytes from 2-, 9- and 24-month-old mice were isolated and the activity of GST was determined spectrophotometrically using 1-chloro-2,4-dinitrobenzene as the substrate. Lymphocyte(More)
Ethmozine, a phenothiazine antiarrhythmic, is effective in atrial and ventricular arrhythmias. Because of the extensive hepatic metabolism of ethmozine, we investigated the effects of the potent hepatic enzyme inhibitor cimetidine on the kinetics and dynamics of ethmozine. Eight healthy men 22 to 40 years old (means = 27.6 years) received a single, oral,(More)
The effects of thyroid status on the activity of hepatic cAMP phosphodiesterase (PDE) were studied in the rat. Male rats were rendered hyperthyroid by treatment with T3 or hypothyroid by treatment with propylthiouracil. The hepatic particulate low Km PDE was solubilized, and its activity was measured at concentrations of 0.12-1.3 microM cAMP. The Km(More)
Because the H2-receptor antagonist cimetidine has been shown to inhibit drug metabolism, the effects of cimetidine on anesthetic metabolism and toxicity were investigated in a rat model. Cimetidine decreased inorganic plasma fluoride production after methoxyflurane administration both in 21% oxygen (P less than 0.001) and in 100% oxygen (P less than 0.001).(More)
The effects of rifampin (600 mg) once daily for 22 days on the total and fractional metabolic clearances of propranolol were determined in a group of six genetically extensive (EM) and six poor metabolizers (PM) of debrisoquin. The impaired ability of PMs to metabolize propranolol to the ring-oxidized metabolite 4-hydroxypropranolol was confirmed. The total(More)
The oral hypoglycemic agent glibenclamide was determined in human plasma by liquid chromatography (LC). Samples, with internal standard added, are extracted with dichloromethane. The organic phase is evaporated, and the residue is reconstituted in mobile phase for injection onto the LC column. Intra- and inter-day variability of the method was assessed at(More)
The need for careful monitoring of plasma concentrations of phenytoin during use of the drug in the treatment of epilepsy is well recognized; there can be great intersubject variation in the absorption rate and clearance rate of the drug, and its therapeutic ratio is narrow. In this study, two methods for determining plasma phenytoin concentrations were(More)