Magnesium attenuates methacholine-induced bronchoconstriction in asthmatics.

The effects of inhaled MgSO4 on methacholine bronchoprovocation test (BPT) were studied in 16 asthmatics in clinical remission (FEV1 greater than 80% of predicted). The patients performed methacholine BPT on two separate days, one day after saline, the other day after MgSO4 inhalation, in double-blind cross-over design. Spirometry was recorded on each test day before and 5 min after NaCl or MgSO4. Neither NaCl nor MgSO4 was found to have a significant effect on spirometric measurements. A significant inhibition of reactivity to methacholine was observed with an increase in log PD20 FEV1 from 1.31 +/- 0.11 inhalation units after NaCl to 1.56 +/- 0.11 inhalation units after MgSO4 (p less than 0.01). The most attractive hypothesis to explain the latter, is that Mg2+ might interfere with Ca2+ handling in the bronchial smooth muscle cells similar to that shown for other types of smooth muscle.