Influence of food intake and sexual segregation on longevity, organ weights and the incidence of non-neoplastic and neoplastic diseases in rats.
In a small-scale experiment the effects of four variables were investigated in male and female Wistar rats fed on a standard laboratory chow and not deliberately exposed to any carcinogen. The variables investigated were (i) diet restriction by limiting access to food to 6.5 hr/day instead of 24 hr/day; (ii) housing males in a single-sex room as distinct from a mixed-sex room; (iii) life-long segregation of males from females, as distinct from access to one virgin female for 5 days during each alternate week; and (iv) uniparity in females versus life-long virginity. The endpoints compared were body-weight gain, longevity, visible and palpable swellings, absolute and relative organ weights, microscopically confirmed malignant neoplasms that contributed to death before the end of the study at 2 yr, incidence of other neoplasms in decedents and rats killed at the end of the study, and the incidence of various non-neoplastic conditions including myocardial inflammation and fibrosis, chronic progressive nephropathy, liver glycogen storage and fatty degeneration, mammary gland hyperplasia and secretory activity, pancreatic polyarteritis, radiculoneuropathy and certain testicular changes. The results indicated major beneficial effects of dietary restriction on most of the endpoints. By comparison the other variables had only marginal effects. Leydig-cell hyperplasia and neoplasia occurred at significantly higher incidences in males housed intermittently with females than in permanently segregated males. No convincing differences were seen between females that littered once and those that remained virgins. The relevance of these findings to the prediction of cancer mortality risk in man and to the design of rodent carcinogenicity studies is discussed.
Salmon
G K
GK
Wellcome Research, Beckenham, UK.
Leslie
G
G
Roe
F J
FJ
Lee
P N
PN
D000818:Animals; D001921:Brain / Q000254:growth & development; D004435:Eating; D005260:Female; D005508:Food Deprivation; D006066:Gonads / Q000254:growth & development; D006321:Heart / Q000254:growth & development; D015994:Incidence; D007668:Kidney / Q000254:growth & development; D008099:Liver / Q000254:growth & development; D008136:Longevity; D008297:Male; D009369:Neoplasms / Q000453:epidemiology / Q000209:etiology*; D009929:Organ Size; D010298:Parity; D051381:Rats; D011919:Rats, Inbred Strains; D012726:Sexual Behavior, Animal; D013047:Specific Pathogen-Free Organisms; D015430:Weight Gain