Immunohistochemical localization of histamine N-methyltransferase in guinea pig tissues

Histamine plays important roles in gastric acid secretion, inflammation, an d allergic response. Histamine N-methyltransferase (HMT; EC 2.1.1.8) is cru cial to the inactivation of histamine in tissues. In this study we investig ated the immunohistochemical localization of this enzyme in guinea pig tiss ues using a rabbit polyclonal antibody against bovine HMT. The specificity of the antibody for guinea pig HMT was confirmed by Western blotting and th e lack of any staining using antiserum preabsorbed with purified HMT. There was strong HMT-like immunoreactivity (HMT-LI) in the epithelial cells in t he gastrointestinal tract, especially in the gastric body, duodenum, and je junum, The columnar epithelium in the gallbladder was also strongly positiv e. Almost all the myenteric plexus from the stomach to the colon was staine d whereas the submucous plexus was not. Other strongly immunoreactive cells included the ciliated cells in the trachea and the transitional epithelium of the bladder. Intermediately immunoreactive cells included islets of Lan gerhans, epidermal cells of the skin, alveolar cells in the lung, urinary t ubules in the kidney, and epithelium of semiferous tubules. HMT-LI was pres ent in specific structures in the guinea pig tissues. The widespread distri bution of HMT-LI suggests that histamine has several roles in different tis sues.