[Effect of pregnancy and lactation on the appearance of the carcinogenic action of N-methyl-N-nitrosourea in rats]. / Vliianie beremennosti i laktatsii na proiavlenie kantserogennogo deistviia N-metil-N-nitrozomocheviny u krys.

ABSTRACT

Female rats were injected intravenously with a single dose of 50 mg/kg N-methyl-N-nitrosourea (MNU). Those of the study group were mated with intact males 30 days later. Some progeny were weaned immediately after birth, and lactation ceased; however, the other females were allowed to feed. There was no relationship between gestation and lactation, on the one hand, and total incidence of tumors of all localizations, on the other, the latter being the same in both the study group and controls. Tumor multiplicity was higher in nullipara and nonlactating females. Gestation and lactation stimulated the incidence of tumors in the kidneys and large bowel as well as polyps in the uterus; however, they were associated with a lower frequency of adrenal adenomas and tumors in the forestomach.