Histamine is present in most mammalian tissues, but its mode of formation is still not clear. According to Blaschko (1945) there are two main theories: (1) Histamine is a vitamin, formed outside the body by bacterial decarboxylation of dietary histidine in the alimentary tract. (2) Histamine is a metabolite, formed from circulating histidine by the histidine decarboxylase present in some tissues of the body.That bacteria form histamine by decarboxylation of histidine is well known (
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