Amine of the imidazole family. It can be produced in the organism by decarboxylation of the amino-acid histidine. Histamine is an excitant of the smooth muscles and is the cause, for example, of contraction of the uterus. It contracts certain arteries and dilates the capillaries, which become more permeable. It has been thought that this released histamine is the cause of the hyperaemia observed in magnesium deficiency.
Mastocytes are particularly numerous in the connective tissues.
This is only a hypothesis. Histamine by itself can produce contractions. It is not impossible, therefore, that copper deficiency may facilitate the direct or indirect effects of histamine on tetany. See Chapter 21 for how these effects combine to finally increase the secretion of adrenaline, the hormone of excitability and the emotions. In Schleswig-Holstein, the German province so seriously affected by grass tetany, soventol is in common use, quite often, apparently, with success.