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.

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Lipolysis and intracellular levels of cyclic AMP of adipose tissue from man and rat in both hypothyroid and euthyroid states were studied in response to stimulation by catecholamines in vitro. Hypothyroid patients were studied before and after treatment, and were also compared with euthyroid obese controls. The experimental group of rats was rendered hypothyroid by the addition of 2.9 mM-propylthiouracil to their drinking water, and their status confirmed by plasma thyroid function tests. Evidence for alpha-adrenergic receptor activity was found in rat adipose tissue, but was less marked than the pronounced alpha-adrenergic activity in human adipose tissue. Glycerol release from adipose tissue in response to noradrenaline stimulation was less marked in hypothyroidism in both species, and was related to an increased alpha-adrenergic activity. No evidence was found for increased alpha-adrenergic effects on cyclic AMP level in hypothyroid subjects, and little evidence was found in adipose tissue from hypothyroid rats. This discrepancy may be due to the presence of the phosphodiesterase inhibitor, theophylline, in the incubation system. The possible modulatory role of thyroid hormones on receptor and phosphodiesterase activity, and on lipolysis, is discussed.

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