The effect of germ-free life and dietary restriction (DR) on life span and pathology was investigated in isolator housed germ-free (GF) and conventional (CV) Lobund-Wistar rats fed either ad libitum or restricted to 12 grams per day (70% of adult ad libitum intake) of a natural ingredient diet from weaning. The median length of life of ad libitum CV and GF rats was 31.0 and 33.6 months respectively, while DR increased the median length of life of CV and GF rats to 38.6 and 37.8 months respectively. DR reduced the frequency or postponed the occurrence of diseases which eventually lead to death in the Lobund-Wistar rat. This was especially true of prostate adenocarcinoma, prostatitis, and mammary fibroma. The reduced early food intake and smaller body weight of adult GF rats may be the reason ad libitum fed GF rats live slightly longer than their CV counterparts, but GF life was without additional effect on life span when food intake was restricted.

Prostate adenocarcinomas were induced in Lobund Wistar rats following subcutaneous implants of silastic chambers containing testosterone propionate. The tumors resembled those that developed spontaneously in the Lobund Wistar rats. Tumors were not induced in ACI rats by the same treatment schedule.

Over the course of 20 weeks, Sprague-Dawley rats developed intestinal tumors in response to an intraperitoneal injection of the acetate derivative of dimethylnitrosamine. The same agent did not induce tumors in Lobund-Wistar rats. The number of tumors was significantly smaller in rats given drinking water containing indomethacin (beginning 14 days after the injections) than in control rats given drug-free water.

Lobund-Wistar (L-W) rats are inherently susceptible to spontaneous and induced metastasizing adenocarcinomas in the prostate-seminal vesicle (P-SV) complex. L-W rats were fed soy protein isolates containing high isoflavones (genistein and daidzein) or low isoflavones to determine their effects on development of induced P-SV tumors in two stages of the tumorigenic process. In rats fed the high-isoflavone-supplemented soy diet before initiation by methylnitrosourea (MNU), the incidence of induced prostate-related cancer was reduced and the disease-free period was prolonged by 27% compared with rats fed the same diet but low in isoflavones. Rats fed the same diets, started after MNU, manifested suggestive but less consistent results than those noted above. The incidence rates were of marginal significance, suggesting that the high intensity of the active induced disease may not represent the character of the slower-growing spontaneous (natural) disease. The delay of disease onset is of clinical significance.

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