The Modifying Influence of Diet and the Physical Environment on Spontaneous Tumour Frequency in Rats

Abstract

THE unusually high frequency of phaeochromocytoma in albino Wistar strain rats bred for many years in our laboratory in Johannesburg compared with that reported from the Wistar Institute by Yeakel (1947) suggested that environmental factors among other conceivable factors were able to influence the development of spontaneous neoplasms in the albino rat (Gillman et al. 1953). It is known that diet can modify the speed of emergence of neoplasms induced experimentally by means of specific carcinogens (Rusch, 1944; Tannenbaum, 1944; Yamagiwa and Itchikawa, 1914;Berenblum, 1954). However, apart from the classical work of McCay (1942) and of Saxton et al. (1948) there is little information about the influence of diet on the frequency of spontaneously-occurring neoplasms in the rat. Moreover, despite its widespread use for studies on experimental cancer, there is a singular lack of statistical information about the risk to cancer of the rat living under a diversity of environmental conditions in different parts of the world.Although it was our original purpose to examine the effects of diet and of geographical factors on the frequency of phaeochromocytoma, the present investigation has been broadened to include a statistical analysis of the kind and frequency as well as the age and sex distribution of other spontaneously-occurring neoplasms. In the presentation of the data, we shall set on record, first, the tumour frequency in terms of age and sex in 586 of our own albino rats (henceforth referred to as the GG strain) receiving the basal diet of the colony and secondly, the effects on tumour frequency of four different diets, none of which decreased the expectation of life.Since we have repeatedly emphasized that climate and other environmental factors may influence the utilization of food (Gillman and Gilbert, 1954) the question arose as to whether albino rats obtained from two different laboratories in Europe would develop the same kinds of tumours as those to be described in the GG strain and whether the pattern of tumour frequency would persist in the migrant strains in subsequent generations, as they do in the GG strain. The results of these several experiments will reveal that whereas the frequency of some tumours remains unaffected that of others is reduced or increased by appropriate manipulation of the environment. Accordingly, attention will be drawn to the need for defining the relative contribution of genetic and environmental factors in promoting the pattern of tumour frequency in a given strain of albino rat.

The Age-related Tumor Incidence in Wistar-Imamichi Rat

“…The occurrence of adrenal gland tumors was high only between 105 and 130 weeks of age, though Gilbert [7] and Gillman [8] reported high age-related incidences in Wistar-GG rats. Previous descriptions have shown that metastasis of tumors was rare in rats [5,16].…”

Spontaneous Pituitary Changes and Their Influence on Mammary Glands in SD Female Rats

“…All (female) [5,17,18,20] ; Wistar rats, 1-60% (male), 2-69% (female) [2,3,7,9,11,12,16,26]; Fischer 344 rats, 15% or 240 (male), 36% (female) [6,21] and Brown Norway (BN/Bi) rats, 14% (male), 26% (female)…”

Effects of Testosterone on the Development of Endometrial Tumors in Female Rats

“…Endometrial cancer rarely develops spontaneously in rats [11], though it can be experimentally produced in rats using polynuclear aromatic hydrocarbons (3-methylcholanthrene, DMBA) [4], In the present 24-week experi ment, no endometrial cancer was observed in rats treated with DMBA alone. This may be due to the DMBAsesame oil solution leaking out from the uterine cavity after administration.…”