Influence of Magnesium on the β-Inhibition of Catecholamines in the Uterine Circular Muscle of Estrogen-treated Rats

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Abstract
The effects of Mg and isoprenaline on the uterine circular muscle of ovariectomized rats which were injected with estradiol for 2-6 days were investigated. The muscle strip exhibited an action potential that was composed of a spike and a plateau and also exhibited a twitch-like contraction due to electrical stimulation. The duration of the action potential became longer when the treatment with estrogen was applied until the maximal effect was built up in 4-5 days. The duration of the action potential and the amplitude of contraction were reduced when isoprenaline was applied. When Mg (0.5 mM) was added to the bathing solution these .beta.-effects were progressively potentiated and the maximal effect was obtained in about 1 h. An increase in membrane conductance was induced by the application of isoprenaline in a control Locke solution and it was further accelerated by exposure to Mg-containing solution. The .beta.-action may be potentiated by Mg ions which penetrated into the membrane.