['Page', '33', 'exposure', 'studies.', 'Normalizing', 'these', 'larynx', 'effects', 'to', 'daily', 'TPM', 'doses', 'reveals', 'a', 'dose-', 'response', 'relationship', 'with', 'no', 'distinction', 'between', 'subchronic', 'or', 'chronic', 'inhalation', 'periods', 'for', 'the', 'squamous', 'metaplasia', '(Figure', '8B)', 'as', 'well', 'as', 'the', 'hyperplasia.', 'Thus,', 'there', 'seems', 'to', 'be', 'no', 'progression', 'with', 'prolonged', 'inhalation.', 'An', 'association', 'of', 'most', 'of', 'the', 'histopathological', 'changes', 'with', 'the', 'particulate', 'matter', 'phase', 'of', 'the', 'SS', 'aerosols', 'was', 'assumed', 'in', 'the', 'previous', 'subchronic', 'study', '(Haussmann', 'et', 'al.,', 'in', 'press).', 'The', 'upper', 'respiratory', 'tract', 'results', 'of', 'the', 'present', 'study', 'support', 'this', 'interpretation', 'and', 'place', 'emphasis', 'on', 'the', 'daily', 'particulate', 'matter', 'dose', 'rather', 'than', 'on', 'concentration', '(WB12', 'vs.', 'HO12', '/', 'WB6).', 'This', 'contrasts', 'with', 'gaseous', 'irritants,', 'such', 'as', 'formaldehyde,', 'which', 'induced', 'epithelial', 'hyperplasia', 'and', 'metaplasia', 'in', 'the', 'anterior', 'part', 'of', 'the', 'nose', 'depending', 'on', 'the', 'concentration', 'rather', 'than', 'on', 'the', 'daily', 'inhaled', 'dose', '(Wilmer', 'et', 'al.,', '1989).', 'The', 'base', 'of', 'epiglottis', 'was', 'the', 'most', 'sensitive', 'site', 'of', 'the', 'respiratory', 'tract', 'in', 'this', 'and', 'the', 'subchronic', 'study', '(Haussmann', 'et', 'al.,', 'in', 'press).', 'The', 'hyperplastic', 'and', 'metaplastic', 'changes', 'seen', 'there', 'were', 'not', 'seen', 'in', 'SS', 'inhalation', 'studies', 'performed', 'by', 'other', 'laboratories', '(von', 'Meyerinck', 'et', 'al.,', '1989;', 'Coggins', 'et', 'al.,', '1993).', 'The', 'only', 'relevant', 'histopathological', 'finding', 'in', 'the', 'lower', 'respiratory', 'tract', 'following', 'chronic', 'RASS', 'inhalation', 'was', 'slight', 'reserve', 'cell', 'hyperplasia', 'in', 'the', 'bronchial', 'respiratory', 'epithelium,', 'which', 'was', 'not', 'seen', 'in', 'the', 'subchronic', 'SS', 'inhalation', 'studies', '(von', 'Meyerinck', 'et', 'al.,', '1989;', 'Coggins', 'et', 'al.,', '1993;', 'Teredesai', 'and', 'Pris,', '1994;', 'Haussmann', 'et', 'al.,', 'in', 'press).', 'It', 'remains', 'to', 'be', 'investigated', 'whether', 'this', 'effect', 'is', 'due', 'to', 'the', 'chronic', 'inhalation', 'period', 'and/or', 'the', 'higher', 'concentration', 'or', 'dose', 'in', 'the', 'present', 'study', 'compared', 'to', 'the', 'previous', 'ones.', 'Morphometric', '2505114234', ' ']