Promotive effect of 4,4'-methylenebis(N,N-dimethyl)benzenamine on N-bis(2-hydroxypropyl)nitrosamine-induced thyroid tumors in Wistar rats.

The promotive effect of 4,4'-methylenebis(N,N-dimethyl)benzenamine (MDBA) on 2-stage thyroid tumorigenesis induced by N-bis(2-hydroxypropyl)nitrosamine (DHPN) in Wistar male rats was investigated. Animals were given i.p. injections of DHPN, and then a basal diet containing 0.0375% MDBA for 19 weeks. In addition, localization of the thyroid-stimulating hormone (TSH) in the pituitary gland was investigated. Levels of TSH and T4 in serum were measured by radioimmunoassay (RIA). The addition of MDBA to the diet significantly increased the incidence and numbers of preneoplastic lesion (focal hyperplasia), adenoma and carcinoma of the thyroid. TSH was usually localized in the thyroidectomy-cell in the anterior lobe of the pituitary gland, and the number of TSH-positive cells increased in the group treated with MDBA. Mean circulating levels of TSH were elevated in all MDBA-treated groups, and mean T4 levels in groups treated with MDBA were significantly lower different (P less than 0.05) than those in control groups.