Effect of magnesium chloride on rabbit bronchial smooth muscle.

Study Objective: The objective of this study was to determine the extent to which magnesium relaxes bronchial smooth muscle during induced contraction.
Design: An in-vitro model using bronchial rings from New Zealand White rabbits stimulated to contract by electrical stimulation, histamine, or bethanechol.
Interventions: Magnesium chloride 1, 6, 16, 36, and 86 mM was added to each tissue bath and resting tension was measured. Electrical stimulation 100 V/100 ms, histamine 10 mM, or bethanechol 6.25 mM was added to washed tissues to induce contraction. This was followed with magnesium chloride 5, 10, and 50 mM, and the response of bronchial smooth muscle was measured.
Measurements and Main Results: Magnesium chloride 1, 6, 16, 36, and 86 mM decreased the mean +/- SEM resting tension of bronchial rings by 40 +/- 16, 100 +/- 11, 110 +/- 10, 170 +/- 9, and 275 +/- 22 mg, respectively. Electrical stimulation (4) of 100 V/100 ms increased the mean +/- SEM resting tension by 168 +/- 52 mg. Magnesium chloride 5, 15, and 50 mM added to the tissue bath decreased the response to 100 V/100 ms to 65 +/- 27, 40 +/- 23, and 1 +/- 0 mg, respectively. Histamine 10 mM (4) increased mean +/- SEM resting tension by 490 +/- 121 mg. Magnesium chloride 5, 15, and 50 mM decreased the histamine response by 80 +/- 56, 250 +/- 74, and 475 +/- 131 mg, respectively. Bethanechol 6.25 mM (14) increased the mean +/- SEM resting tension by 495 +/- 74 mg. Magnesium chloride (5, 15, 50 mM) decreased bethanechol-induced tension by 52 +/- 18, 184 +/- 26, and 506 +/- 64 mg, respectively.
Conclusion: Magnesium chloride produced dose-dependent relaxation of bronchial smooth muscle at rest and when stimulated by histamine, bethanechol, or electrical impulse. Calcium chloride was unable to significantly reverse magnesium-induced relaxation. These data support the hypothesis that magnesium relaxes smooth muscle and dilates bronchial rings.