Selenium is an essential component of glutathione peroxidase, an enzyme that helps protect cells against oxidation damage and modulates the lipoxygenase pathway of arachidonic acid metabolism. Low selenium concentrations might therefore influence the inflammatory process in asthma by reducing the activity of glutathione peroxidase. Whole blood and plasma selenium concentrations and glutathione peroxidase activity have been measured in 56 asthmatic patients and 59 non-asthmatic control subjects in New Zealand, a country with a low dietary selenium intake and a high prevalence of asthma. When compared with control subjects the asthmatic patients had lower values for whole blood selenium concentrations (-4.9, 95% confidence interval -102 to 04 ng/ml) and glutathione peroxidase activity ( -3 3, 95% CI -58 to -0O8 unitslg Hb). There was a 19 and 5 8 fold increased risk of asthma in subjects with the lowest range of whole blood selenium concentration and glutathione peroxidase activity respectively (95% CI 0-6 to 5 6 and 1-6 to 21-2).Levels were lower in patients and control subjects without an atopic predisposition, but were not affected by prednisone use. Similar differences between the asthmatic and control subjects were not observed for selenium concentration or glutathione peroxidase activity measured in plasma, which reflects short term rather than long term selenium content.
The hypokalaemic effects of equal doses (5 mg) of fenoterol, salbutamol, terbutaline and an equal volume of saline administered by nebulization were compared in eight healthy subjects. Plasma potassium was measured at 15-min intervals for 60 min and at 90 min, 2, 4 and 6 h following administration. Fenoterol, salbutamol and terbutaline all significantly decreased plasma potassium when compared to saline; however, the magnitude and duration of this effect differed between the active agents. Both fenoterol and terbutaline significantly reduced plasma potassium for 4 h whereas salbutamol was only different from 30 to 120 min. The maximum decrease occurred with fenoterol (-0.78 mmol/l), followed by terbutaline (-0.70 mmol/l) and salbutamol (-0.33 mmol/l). Both terbutaline and fenoterol had a significantly greater effect compared with salbutamol. When administered by nebulization fenoterol and terbutaline are likely to have a greater hypokalaemic effect than salbutamol and this effect is likely to be more long lasting.
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