Aging and Dietary Modulation of Rat Skeleton and Parathyroid Hormone*

Abstract

Studies were carried out on SPF F344 male rats to evaluate the effects of aging and life-prolonging food restriction, without malnutrition, on rat skeleton and circulating PTH. Six-week-old F344 rats were divided into five groups. Group 1 rats were fed ad libitum a diet that contained 21% protein. Group 2 rats were fed 60% of the mean food intake of group 1 rats from 6 weeks of age for the rest of their lives. Group 3 rats were fed 60% of the ad libitum food intake until 6 months of age and then switched to ad libitum feeding. Group 4 rats were fed ad libitum until 6 months of age, and then switched to 60% of the ad libitum food intake. Group 5 rats were fed ad libitum a diet that contained only 12.6% protein so that these animals ingested the same amount of protein per day as the group 2 rats. In group 1 animals, bone length, weight, density, and calcium content increased rapidly with age and plateaued at about 12 months of age. There was no evidence of bone loss in these animals until about 24 months of age, but by 27 months, the animals had lost appreciable amounts of bone. The circulating immunoreactive PTH levels of the animals increased with advancing age, with a marked rise at 27 months. The age-related changes in bone and serum PTH levels of rats in groups 3 and 5 were similar to those of group 1 animals, except that a terminal increase in serum PTH did not occur in group 5 rats. In the groups 2 and 4 animals which were food restricted for the longest period, bone growth and maturation were slowed down, but the animals did not experience senile bone loss or marked terminal increase in circulating PTH. The salutary effects of food restriction were, therefore, not due specifically to the restriction of protein intake or to restricting food intake only during the period of rapid growth.

Age-Related Changes in Bone Mineral Density, Cross-Sectional Area and Strength at Different Skeletal Sites in Male Rats.

“…The greater increase in the SSI values of long bones and the change in first lumbar vertebra might be due to these morphological changes. This might be related to almost no change in organic components with increasing age [11,[13][14]. The age when rats show the so-called peak of bone mass in the whole skeleton was not clearly determined from the results obtained in this study.…”

“…According to previous studies, the high BMD or calcium content of the first and fourth lumbar vertebrae, femur, and tibia coincided with a high testosterone level at the age of 12 months in male Wistar rats [11,14,17]. On the other hand, no change in the BMD of the femur measured by DEXA in male rats was observed after the rats had reached maturity [19].…”

Aging mechanism as the “down side” of adaptation: A network approach

“…brain maturation could be compared at similar ages in calorically restricted and normal model organisms. In support of this view, the effects of caloric restriction show a decrease in the normal rate of maturation in both rodents (Kalu et al, 1984;Merry & Holehan, 1981) and rhesus monkeys (Mattison et al, 2003). Interestingly, caloric restriction seems to have reduced effects on longevity if applied after middle age, i.e.…”

Skeletal effects of long-term caloric restriction in rhesus monkeys

“…The earliest study (McCay et al 1935) found that femurs removed from restricted (R) rats crumbled during dissection; however, the level of CR makes it likely that these animals were suffering from nutritional deficiencies. Later studies by Kalu et al (1984aKalu et al ( , b, 1988 in F344 rats under a less severe restriction found that CR resulted in delayed epiphyseal closure, bones of lower density, and no reduction in femur density in old age. Results from more recent rodent studies have been variable.…”