Abstract
Life length, survival patterns and histological change of rats has been studied at the different dietary protein level.
Male weaning rats received synthetic diets containing three different levels of casein on ad libitum feeding as well as pair-feeding. In 10 and 18% casein group the diets were given throughout the life, and in 27% casein group rats were raised with 27% casein diet during the first one year, and then all of the surviving rats were devided into three groups, in which each 10, 18 and 27% casein diet was fed until death.
In the case of the uniform lifelong dietary regimes, there was no statistically significant difference among the mean life length of rats in 10, 18 and 27% casein group. However, the following tendencies were observed from the viewpoint of effect of dietary protein level on life span. On ad libitum feeding 18% casein diet was most beneficial, and 27% casein diet was superior to 10% casein diet during the first 540 days, and thereafter in late life 10% casein diet was better than 27% casein diet. On pairfeeding, 27% casein diet was the best, and there was no marked difference between 10 and 18% casein diet.
18% casein diet seemed to produce most favorable influence on length of life among three kinds of diets, which were given to the rats in 27% casein group from one year old age to death.
Mean length of life was not significantly different among rats in different litters under the same dietary condition.
The results of histological post mortem examination were as follows. The major cause of death was pneumonia. Lower the casein level in the diets, more incidence of lesions in the liver was observed. Especially atrophy of the liver was observed in high rate even during the first one year in 10% casein group, but the incidence of fatty liver did not related to the caseinlevel in diets. Myocardial degeneration, especially pimelosis, developed more frequently in 27% casein group than in other two groups. Atrophy of the testis and calcification in the kidneys occured more frequently in 10% casein group than in other two groups. Less incidence of lesions in the heart, kidneys, testis, stomach and intestine was observed in 18% casein group than the other groups. Only a few rats had lesions in the spleen and adrenals microscopically observable. No histological change was found in the brain.
