“In a normal solution, Mg++ increased the EC50 value for histamine , but did not alter the EC50 value for norepinephrine or the maximum force induced by norepinephrine or histamine.”
“The results indicate that in the pulmonary artery, Mg++ alters the sensitivity to histamine but not to norepinephrine, and may differentially inhibit bound Ca++ release by norepinephrine and histamine.”