Effect of triiodothyronine and reserpine on induction and growth of mammary tumors in rats by 3-methylcholanthrene

MNU-induced carcinogenesis of rat mammary gland: effect of thyroid hormone on expression of retinoic acid receptors in tumours of mammary gland

The rat model of N-methyl-N-nitrosourea (MNU)-induced mammary carcinomas is well-established animal model for breast cancer. This study was carried out to investigate whether hypothyroid (thyroidectomy or PTU treatment) or hyperthyroid status of female rats would affect MNU-induced mammary carcinogenesis with specific focus on both retinoid and rexinoid receptor expression in mammary tumours. Application of PTU before and during MNU-induced mammary gland carcinogenesis yielded in a marked decrease of the number and volume of tumours per animal, however, there was no effect of hypothyroid state in thyroidectomized rats as well as hyperthyroid state concerning the number and volume of tumours. Mammary tumours of in euthyroid group of MNU animals showed that there was no tumour, in which all of subtypes of retinoid and rexinoid receptors were expressed. A different pattern of expression of retinoid or rexinoid receptors was found either in MNU-induced mammary carcinomas in both hypothyroid and hyperthyroid rats.