Influence of hormonal disturbances on transplacental and multigeneration carcinogenesis in rats.

: Thyroid dysfunction (induced by thyroidectomy or administration of thyroxin and methylthiouracil) during the postnatal period was tested as a modifying factor on carcinogenesis induced transplacentally by N-methyl-N-nitrosourea (MNU). It resulted mainly in inhibition of tumours of the nervous system and kidney in rats of two subsequent generations, but thyroid carcinogenesis was increased. Postnatal disturbance of oestrous function (induction of persistent oestrus syndrome) in female rats increased the incidence of tumours of the central nervous system induced transplacentally by MNU or 7,12-dimethylbenz[a]anthracene. No such effect was seen in animals of the F2 generation.