Maternal handling during pregnancy reduces DMBA-induced mammary tumorigenesis among female offspring.

The present study investigated whether handling of pregnant rats would affect mammary tumorigenesis in their female offspring. Pregnant Sprague-Dawley rats were injected daily with 0.05 ml of vehicle between days 14 and 20 of gestation or were left undisturbed. Handling did not have any effects on pregnancy or early development of the offspring. The female offspring were administered 10 mg of 7,12-dimethylbenz(a)anthracene (DMBA) at the age of 55 days. The rats whose mothers were handled during pregnancy had a significantly reduced mammary tumour incidence when compared with the offspring of non-handled mothers. Thus, on week 18 after DMBA exposure, 15% of the handled offspring had developed mammary tumours, whereas 44% of the non-handled offspring had tumours. No significant differences in the latency to tumour appearance, in the size of the tumours or in their growth rates were noted. Daily handling performed during post-natal days 5 and 20 produced similar data to that obtained for prenatal handling; on week 18 after DMBA exposure, the mammary tumour incidence among the post-natally handled rats was 22% and among the non-handled rats 44%. Possible deviations in hormonal parameters were also studied in adult female rats exposed in utero to handling. The onset of puberty tended to occur later among the handled offspring, but no differences in the uterine wet weights or serum oestradiol levels between the groups were noted. In conclusion, maternal handling reduced the offspring's risk to develop mammary tumours, and this effect was independent of the oestrogenic environment at adulthood. We propose that handling of a pregnant rat reduces mammary tumorigenesis in her offspring by means of changing the morphology of the mammary gland, the pattern of expression of specific genes and/or immune functions.