Thyroid modifications in male and female rats treated with the hepatocarcinogen beta-blocker ZAMI 1305.

The morphology of the thyroid gland from Wistar rats treated for 6 months with the beta-blocker DL-1-(2-nitro-5-methyl-phenoxy)-3-tert-butyl-amino-propan-2-ol (ZAMI 1305), a potent sex-dependent hepatocarcinogen, was studied. A significant high incidence of cases with thyroid hyperplasia is found among female rats, the only sex susceptible to the carcinogenic effect of ZAMI 1305. Thyroid hyperplasia is instead much less evident in male rats. In female rats the increase in the relative thyroid weight is directly related to the gravity of the predominant liver lesion (clear cell foci, neoplastic nodules, hepatocellular carcinomas). The results suggest an influence of the preneoplastic and neoplastic liver on thyroid gland.