Influence of tobacco smoke on DNA unwinding and uterotrophic effect of estrogens in rats.

Experiments with a duration of either 3 weeks or 3 months were conducted on female rats with initial body weights of 140-170 g. All animals were divided into four groups, i.e. control, tobacco smoke (TS, a whole-body exposure to the mainstream cigarette smoke), estrogen (EG, diethylstilbestrol) and TS + EG. Injection of EG started on the day of bilateral ovariectomy which was performed in all animals 11 days before the end of the experiment. In short 3-week experiments TS weakly stimulated uterine wet weight and in combination with EG significantly increased the percentage of intact non-unwound DNA in uterine tissue (stimulation stage). In the longer 3-month experiments TS decreased a specific hormonal effect of EG, i.e. the ability to induce progesterone receptors in uterine tissue, and did not interfere with the DNA-damaging effect of diethylstilbestrol. The conclusion was made that different phases exist in hormonal and genotoxic responses to the combined effect of tobacco smoke and estrogens, which may be related to the mechanisms and types of hormonal carcinogenesis.