Response of rat lung to 3,4-benzpyrene administered by intratracheal instillation in infusine with or without carbon black.

In a controlled experiment groups of SPF Wistar rats were give 18 once-fortnightly doses of 0-5, 1-0 or 2-0 mg 3,4-benzpyrene (BP) suspended in infusine (I) or in carbon black (CB) + I by intratracheal instillation. Of rats examined post mortem, 1/16 given I+CB only, 0/16 given I only, 15/51 given BP in I+CB and 24/48 given BP in I developed squamous neoplasms of the lung. The incidence of tumours was significantly related to dose of BP. At the 1 or 2 mg dose levels BP in I only was more productive of tumours than BP in I+CB. Other changes encountered included squamous metaplasia of alveolar and bronchiolar epithelium (Sq.M), but not of bronchial epithelium, and cuboidal and columnar metaplasia of alveolar epithelium in the vicinity of terminal bronchioles (CCM). Sq.M was associated with exposure to BP or I+CB. CCM was strongly associated with exposure to I+CB but only weakly with exposure to BP.