Young male rats were fed diets containing 0, 1, 10, or 100 ppm of Firemaster (FM) BP-6 for 30 days and thyroidal and hypophyseal effects were compared with those caused by feeding identical amounts of either 2, 2', 4, 4', 5, 5'-hexabromobiphenyl (HBB) or 2, 3', 4, 4',5,5'-HBB, two of the congeners in FM BP-6. In addition, rats were given dietary levels of 0,1, or 10 ppm of 3,3', 4,4', 5, 5-HBB, a congener not in FM BP-6, but used because it is a 3-methylcholanthrene (MC)-type inducer of hepatic drug metabolizing enzymes. Thyroid weight was increased by 100 ppm FM BP-6 and by 1 and 10 ppm 3, 3', 4, 4', 5, 5'-HBB. Serum thyroxine concentrations were decreased by the highest dose of the same two chemicals. Extensive hyperplasia and hypertrophy of follicular cells and a lack of colloid were prominent lesions at the highest doses of each of the chemicals. The most severe ultrastructural alterations were seen at 10 ppm 3, 3', 4, 4', 5, 5'-HBB and 100 ppm FM BP-6. A dramatic increase in lysosomal bodies was seen at these doses. In addition, cytoplasmic colloid droplets were increased and microvilli were decreased. The Golgi apparatus was hypertrophied and the cisternae of the reticulum were dilated. Lesions were less severe with 2, 2', 4, 4', 5, 5-HBB and 2, 3', 4, 4', 5, 5-HBB, although more lysosomal bodies were seen with 2, 3', 4, 4', 5, 5-HBB than with 2, 2', 4, 4', 5, 5-HBB. Chromophobe cells in the pars anterior of the pituitary gland were swollen and vacuolated in rats fed diets containing 10 ppm 3, 3', 4, 4', 5, 5'-HBB. The results indicate that histologic and ultrastructural changes can occur with any of the chemicals used but the major functional and ultrastructural thyroidal changes seen in rats given FM BP-6 are most likely caused by congeners other than 2, 2', 4, 4', 5, 5-HBB or 2, 3', 4, 4, 5, 5-HBB.
Differential induction of hepatic drug-metabolizing enzymes by fenvaleric acid in male rats