RESUMO
It is well known that not all strains of laboratory rats are suitable for use as an experimental animal model for tumour development; hence, in every article published, the strain of rats used in the research is always accurately stated. Before 1984, the stock in the Mona-Preclinical Animal House comprised Wistar rats. These rats were susceptible to the development of breast tumours. The present Mona stock of rats is the product of an inbreeding between the old Wistar and Sprague-Dawley rats, the later introduced into the colony in 1984 by the Biochemistry Department for experimental purposes. After the experiments were completed, these rats were used for interbreeding with the Wistar rats. In 1999, experiments were started to develop breast tumours in the female rats of this mixed breed. A carcinogen (DMBA) was administered intragastrically into 14 females rats and after 10 months of observations, 13 (93 percent) developed tumours, while in the same period no tumours were found in the controls (13 female rats). Therefore, it can be stated that the present stock of rats is still suitable as an animal model for the development of breast tumours. Experiments to develop prostatic cancer in the male rats are in progress. It is suggested that authors of articles reporting the results of research using the Mona colony of rats should clearly state that the "Mona strain' of white rats used. To further establish this Mona strain, improved maintenance and breeding methods should be implemented and also collection of basic data such as average litter size, birth weight, growth curve and incidence of the development of spontaneous tumours should be stated.(Au)
