The effect of changing the amount of polyunsaturated fat in the diet of aged female Fischer 344 rats at the time of
tumor implant on
metastasis from the 13762 transplantable mammary
tumor was studied. Three experiments were performed. (a) Retired breeders, maintained on standard commercial chows until 10 to 12 mo of age, were transferred to high fat (HF, 23%
corn oil) or low fat (LF, 5%
corn oil) diets for 4 wk; at
tumor implant, half of each group were kept on their original diets, while half were changed to the other diet (i.e., HF----HF, HF----LF, LF----LF, LF----HF). (b) Aged virgins, 14 to 16 mo old, were fed HF and LF diets from weaning; at
tumor implant, the LF group stayed on the LF diet, while half the HF group remained on the HF diet and half were changed to LF. (c) Retired breeders were fed Purina rodent chow (5% mainly saturated fat) until
tumor implant when they were placed on either the HF or LF diets. Six wk after
tumor implant, all rats were necropsied, and the extent of pulmonary
metastasis was determined. Data were expressed as volume of pulmonary
metastases. In Experiment 1, animals maintained on a HF diet or changed to a HF diet at implant had significantly more pulmonary
metastases than those animals kept on a LF or changed to a LF diet. Likewise in Experiment 2, pulmonary
metastasis was less in rats which were fed a HF diet from weaning and then changed to LF at
tumor implant than in the animals maintained on a HF diet both before and after
tumor implant. Finally, in Experiment 3, when rats were changed from Purina rodent chow to either the HF or LF diet at
tumor implant, there was no significant difference in the extent of pulmonary
metastasis between the two groups; in both, the extent of
metastasis was comparable to that seen in animals maintained on the LF
corn oil diet. Data on
metastasis were also examined in light of
body weight, growth of the primary
tumor, and food disappearance. These results suggest that the amount of fat consumed by aged rats after
tumor implant is an important determinant of the extent of pulmonary
metastasis from the 13762 mammary
tumor. However, a period of prefeeding the semipurified diets appears to be required in order for the HF
corn oil diet to stimulate
metastasis in this system.