title: Ultrastructure of Clara cells stimulated by isoproterenol.
abstract: The incidence of peripheral pulmonary adenocarcinoma has increased in recent years. Clara cell has been known as target for carcinogens and source of pulmonary tumors. One of the presumed roles of the bronchiolar Clara cell is the secretion of pulmonary surfactant into the bronchiolar lumen. To establish the secretory morphology of Clara cell, a well-defined secretory agonist, isoproterenol (500 mg/kg) and the antagonist, propranolol (20 mg/kg), were administered into five-week old mice. The secretory response was examined at 1 hour and 4 hours after injection. Ultrastructural morphometry was used to quantitate the secretory response by measuring area of apical cap of the Clara cells. Isoproterenol caused a significant increase in area of apical cap of Clara cells 1 and 4 hours after injection (p < 0.0001), while pretreatment with propranolol prevented this effect at 4 hours. Propranolol alone significantly decreased the area of Clara cells (p < 0.0001). Clara cells secretory granules disappeared 1 hour after propranolol plus isoproterenol administration, and the granules reappeared at 4 hours. The accelerated secretion of Clara cells by isoproterenol provides evidence of their secretory mechanism controlled by beta-adrenergic agonists. The study has confirmed the secretory role of Clara cells. The secretion is both apocrine and merocrine type.
authors.affiliation: Department of Human Pathology, Digestive and Metabolic Disease, Tokyo Medical and Dental University, Graduate School, Tokyo, Japan.
authors.forename: Gopi
authors.initials: G
authors.lastname: Aryal
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kimula
authors.forename: Morio
authors.initials: M
authors.lastname: Koike
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000187:drug effects* / Q000648:ultrastructure; D048429:Cell Size / Q000187:drug effects; D003593:Cytoplasm / Q000187:drug effects / Q000648:ultrastructure; D004847:Epithelial Cells / Q000187:drug effects / Q000648:ultrastructure; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D011433:Propranolol / Q000494:pharmacology; D011663:Pulmonary Surfactants / Q000378:metabolism; D022142:Secretory Vesicles / Q000187:drug effects / Q000648:ultrastructure; D013997:Time Factors
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D011663:Pulmonary Surfactants; D011433:Propranolol; D007545:Isoproterenol