The Mechanism of Morphine-Induced Urticaria

To the Editor.—  Opiates are known to cause histamine release that may produce urticaria.¹ MacIntosh and Paton showed that a wide range of basic compounds, of comparable or increased basicity to histamine, can release histamine from mast cells, probably by an ion-exchange mechanism.² Opiate-induced histamine release has been classified in this group, but, in recent years, opiate receptors have been found to be widely distributed, and it was wondered whether opiate-induced histamine release occurred via specific receptors instead.In vitro studies were carried out using fresh normal human skin obtained from surgical procedures. The skin was chopped into small pieces, washed with Tyrode's solution, and then divided into equal-sized samples. The samples were incubated in Tyrode's solution for five minutes at 37 °C, and then the potential histamine releaser was added. Concentrations of morphine sulfate between 10^-9 and 10^-3M were used with control subjects. After