Histamine reduces the deamination of putrescine in vitro--but also in vivo?

The diamine oxidase catalysed deamination of putrescine was reduced in vitro by histamine at concentrations occurring in the gut. An oral application of histamine, however, had no effect on the enzymic activity. When the histamine was injected i.p. a decrease of intestinal diamine oxidase activity was observed which, however, did not depend on histamine but probably on an unspecific irritation of the gut.