Histamine is β imidazolylethylamine. It is synthesized locally from the amino acid histidine and degraded rapidly by oxidation and methylation.
SYNTHESIS, STORAGE AND DESTRUCTION
Histamine is β imidazolylethylamine. It is synthesized locally
from the amino acid histidine and degraded rapidly by oxidation and methylation
(Fig. 11.1). In mast cells, histamine (positively charged) is held by an acidic
protein and heparin (negatively charged) within intracellular granules. When
the granules are extruded by exocytosis, Na+ ions in e.c.f. exchange with
histamine to release it free (Fig. 11.2). Increase in intracellular cAMP
inhibits histamine release. Histamine is inactive orally because liver degrades
all histamine that is absorbed from the intestines.
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