Study of the post-natal effects of chemopreventive agents on ethylnitrosourea-induced transplacental carcinogenesis in rats. II. Influence of low-molecular-weight polypeptide factors from the thymus, pineal gland, bone marrow, anterior hypothalamus, brain cortex and brain white substance.

The influence of the polypeptide factors extracted from thymus, pineal gland, bone marrow, anterior hypothalamus, brain cortex or brain white substance on N-ethyl-N-nitrosourea (ENU)-induced transplacental carcinogenesis was studied in rats. ENU was given to pregnant rats as a single i.v. exposure at a dose of 75 mg/kg body weight on the 21st day of gestation. The polypeptide factors were given to the offspring as a series of s.c. injections, at a dose of 0.5 mg/rat/day, starting at one or 2.5 months of age and continuing throughout the whole of post-natal life. ENU induced tumors of the brain, spinal cord, peripheral nerves and kidneys in 94-98% of the offspring exposed to the carcinogen, with an average number of 2.3-2.6 tumors per rat, and an average survival time of 294 days. Post-natal thymus factor or pineal gland factor administration was followed by an increase in mean lifespan of approximately 2 months and a significant decrease (P < 0.05) in the total tumor number per tumor-bearing rat, as well as the incidence and multiplicity of spinal cord tumors. Pineal gland factor also decreased the incidence of peripheral nerve and kidney tumors and their number per tumor-bearing rat. Brain cortex factor and brain white substance factor treatment was followed by a decrease in total tumor multiplicity of 1.2- to 3.3-fold, and a decrease in incidence of brain tumors of 10 to 33% per rat in comparison to the controls. Brain cortex factor also decreased the total tumor incidence. At the same time, brain white substance factor administration increased the incidence of peripheral nerve tumors and decreased the mean lifespan. Both bone marrow factor and anterior hypothalamus factor did not have any modifying effects on any of the ENU-induced tumors and mean lifespan. Thus, our results show the possibility of attenuation of transplacental ENU-induced carcinogenesis with post-natal administration of some polypeptide substances.