Autochthonous prostate adenocarcinomas in Lobund-Wistar rats: a model system

The promotional effect of testosterone on induction of prostate-cancer in MNU-sensitized L-W rats

Large metastasizing prostate adenocarcinomas (PAs) were induced in L-W rats by a single intravenous (i.v.) inoculation of methylnitrosourea (MNU) and then single subcutaneous implants of testosterone propionate (TP) at intervals of 2 months. This procedure induced PAs in approximately 90% of rats in an average of 11 months. PAs did not develop spontaneously in L-W rats under age 20 months. With this model system, it was demonstrated that within a 14-month observation period, significant numbers of PAs were elicited by TP implants in L-W rats after intervals of 1 week, 1 month and 2 months following the inoculation of MNU. A direct relationship was also demonstrated between amount of TP administered to L-W rats and the resulting incidence of PAs. TP is characterized as a prostate-directed promoter of PA, following a single inoculation of MNU which served as the tumor initiator.

Prevention and treatment of experimental prostate cancer in Lobund-Wistar rats. I. Effects of estradiol, dihydrotestosterone, and castration

The Lobund-Wistar (L-W) rat is unique in its susceptibility to spontaneous and induced metastasizing prostate adenocarcinomas (PAs). A single IV inoculation of methylnitrosourea (MNU) produced PAs in 20% of L-W rats in 12 months. The combination of MNU plus two to seven slow-release implants of testosterone propionate (TP) induced PAs in 50-90% of rats respectively in an average of 11.5 months. The induction of PAs was prevented by early treatments of rats at risk with estradiol and less so with dihydrotestosterone (DHT). However, on a technical basis, the results were not significant. Treatments of MNU-inoculated rats with estradiol, with DHT, or by castration, at intermediate points in the projected latency time of tumor development, reduced significantly the incidences of PA development. Rats in which overt PAs had already developed in response to 12 months of exposure to implants of TP did not respond to treatment by estradiol, DHT, or castration. Thus there are early stage(s) in induced prostate tumorigenesis in L-W rats that are sensitive to modulating agents.