The influence of aging on intestinal absorption of vitamin B12 and niacin in rats.

The intestinal absorption of doses of vitamin B12 and of niacin was examined in 6, 12, and 24 months old female Wistar rats. Rats were dosed via stomach tube with radioactive forms of the vitamins and were killed 16 hours later. Percent of the dose remaining in the stomach and gastrointestinal tract and in the collected feces was determined. Absorption of the two vitamins was not influenced by the age of the animals.

The influence of aging on intestinal absorption of vitamins A and D by the rat.

The absorption of vitamins A and D was examined in 6, 12, and 24 months old female Wistar rats. Animals were dosed by stomach tube with radioactive forms of vitamins A and D and killed 18 hours later. Isotope in feces collected during this time and isotope remaining in the gastrointestinal tract were determined and subtracted from total dose to determine percentage of absorption. Under the conditions of this study, age had no significant effect on the absorption of vitamins A and D.

Effects of age and dietary restriction on the kidney glomeruli of mice: observations by scanning electron microscopy.

A study was undertaken to examine, by scanning electron microscopy (SEM), the kidney glomeruli of control mice 1 mo, 10 mo, and 24 mo of age, as well as dietarily restricted mice 10 mo and 24 mo of age. One month old female C57BL/6J mice were offered one of the following: 1) a control diet containing 24% protein fed ad lib; 2) the control diet fed on alternate days (intermittently fed); or 3) a diet containing 4% protein fed ad lib. Animals were sacrificed, by aldehyde perfusion at 1 mo, 10 mo, and 24 mo of age. The kidneys were sliced and prepared for SEM. There was a significant age-related increase in glomerular diameter and amount of microvilli on the podocyte surface (microvillus index). Although the diameters of the podocytes increased approximately 20% with age, these differences were not statistically significant. Feeding a 4% protein diet resulted in smaller diameters of glomeruli and podocytes as well as smaller microvilli indices as compared to those of control animals. Although similar differences were observed in the kidneys of intermittently fed animals, only the microvillus index was statistically significant. Therefore, dietary manipulations, which have been shown to increase life span, result in marked morphological differences when compared to control animals.

The effect of various dietary restricted regimes on biochemical variables in the mouse.

Twenty-one day old and seventeen month old female mice were fed the following three dietary regimes for one or six months: 1) 24% protein ad libitum; 2) 4% protein ad libitum; or 3) 24% protein intermittently fed (diet offered for twenty-four hours on Monday and Wednesday, and for eight hours on Friday). The activities of succinoxidase, malic dehydrogenase and cholinesterase as well as the concentrations of protein and DNA were determined in livers and kidneys. Calculated on the basis of DNA, the activities of these three enzymes as well as protein content were decreased in the 4% and intermittent-fasted animals and increased in the intermittent-fed animals. The mean values of the enzymes as well as the protein content per mg. of DNA of the intermittent-fed and intermittent-fasted animals were essentially the same as that of the 24% ad libitum controls. These findings were obtained on both young-growing and adult animals. INDEX WORDS: Dietary restriction, enzymes, age, mouse, protein synthesis, genetic code use.

Dietary protein, life-span, and biochemical variables in female mice.

The 50% mortality of female C57BL/6J mice fed ad libitum a diet which contained 26% or 4% casein, was 23.5 and 28 mo., respectively. Diet did not markedly affect the age-associated changes in the collagen content of the extractability of collagen of skin. In general, the activities of enzymes based on DNA were low in the restricted animals.

Dietary protein life-span, and physiological variables in female mice.

The 50% mortality of female C57BL/6J mice fed ad libitum a diet which contained 26% or 4% casein, was 23.5 and 28 mo., respectively. Significantly lower rectal temperatures and higher oxygen consumptions were observed in the animals offered the 4% compared to the 26% casein diet. Changes in body temperature and oxygen consumption could not account for the total increase in life-span brought about by feeding a low protein diet.

Protein synthesis, development, growth and life span.

To test the hypothesis that reduced protein synthesis may increase life span by retarding genetic informational transfer during early life and reducing the use of the genetic code and thereby minimizing genetic imperfections as they may occur during late life, two approaches were used. In the first protein synthesis was depressed by the administration of cycloheximide, in the second by reducing the dietary protein level. One-day-old chick embryos were injected with either 0.8 gamma or 1.0 gamma of cycloheximide. On the second and third day of incubation both stage of development and heart rate were lower in the treated embryos. Growth was retarded throughout the 17 days of incubation as measured by size and DNA contents. As estimated by the activities of various enzymes per unit DNA, cells of the treated embryos were the same as normal ones of the same age. Sixteen-month-old female Wistar rats which had been previously maintained on a commercial diet (23.4% protein) were fed diets which contained either 24, 12, 8 or 4% casein throughout their remaining life span. Except for a lowering of the body weights of the animals fed the 4% casein diet, the body weights of the remaining animals were unchanged. Reducing the dietary protein level from 24% to 12% increased the life span (25%) of the animals.