Effects of Histamine H1r-H4r-Agonist on the Airway Epithelium of Rabbits

Objective: To explore the exact role of histamine receptors in respiratory system. Methods: The cohort comprised of six groups (group I control and group II-VI treated) containing five rabbits in each group. Control-group received vehicle (sterile distilled water) and treated groups received subcutaneous histamine (100 mu g/kg, b.i.d.), and H1R-agonist (HTMT), H2R-agonist (amthamine), H3R-agonist (R-(-)- alpha -methylhistamine) and H4R-agonist (clobenpropit) each in a dose of 10 mu g/kg, b.i.d. for 30 subsequent days. After completion of treatment, animals were euthanized and perfused with 10% buffered formalin. Small tissue blocks of trachea and lungs were processed for paraffin embedding. Observations were recorded in sample photomicrographs taken from 10 mu m thick. Haematoxylin and eosin stained sections. Results: It was observed that trachea and bronchi from histamine, H1R and H4R groups had only patches of hyperplastic and hypertrophied epithelium and in general, cells in the affected region were taller heaped up. The bronchiolar epithelia from all treated groups showed hypertrophy and hyperplasia throughout with most of the cells having rounded profile and appeared to bud out from the basal cells. Conclusions: It is concluded that histamine receptors on induction via its specific agonist can induce hypertrophy, hyperplasia of respiratory tract epithelia suggesting its role akin to growth stimulating factor and warranting further long-term study.