Interactive environmental and genetic effects on longevity in the male rat: litter size, exercise, electric shocks...

The effects on longevity of manipulating litter size during rearing and of postweaning forced exercise were observed in intact and castrated male rats. Random-bred sib quintets of newborn littermates were reared in reduced litters or normal litters (5 or 6, or 10-12 young, respectively). The quintets were split into five postweaning treatments: untreated (control), exercised (forced to run by electric shocks), shocked (without exercise), castrated, and castrated and exercised. Reduced litter size increased weaning weight from 46 to 56 g and diminished mean longevity from 724 to 620 days. The decrease in longevity due to reduced litter size was greater in the control (204 days) than in the other postweaning treatments (42 to 142 days). The postweaning treatments affected longevity only in the reduced-litter males; in these, exercise and mere shocks appeared to increase longevity. The variation in longevity among quintets was large and the expression of genetic longevity interacted with the treatments. The regression of individual on mean sib longevity was .89 in the castrates but only .10 in the controls; in exercised and shocked males it was .58 in normal-litter but only .09 in reduced-litter sibs indicating an interaction between pre- and postweaning treatments. The implications of the results on the interpretation of longevity studies are discussed.