Kalu D N, Hardin R H, Cockerham R, Yu B P
Endocrinology. 1984 Oct;115(4):1239-47. doi: 10.1210/endo-115-4-1239.
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.
对无特定病原体(SPF)的F344雄性大鼠进行了研究,以评估衰老以及无营养不良的延长寿命的食物限制对大鼠骨骼和循环甲状旁腺激素(PTH)的影响。六周龄的F344大鼠被分为五组。第1组大鼠随意进食含21%蛋白质的饮食。第2组大鼠从6周龄开始,余生进食量为第1组大鼠平均进食量的60%。第3组大鼠在6月龄前进食量为随意进食量的60%,之后改为随意进食。第4组大鼠在6月龄前随意进食,之后改为随意进食量的60%。第5组大鼠随意进食仅含12.6%蛋白质的饮食,以使这些动物每天摄入的蛋白质量与第2组大鼠相同。在第1组动物中,骨长度、重量、密度和钙含量随年龄迅速增加,并在约12月龄时趋于平稳。在约24月龄前这些动物没有骨质流失的迹象,但到27月龄时,动物已经流失了相当数量的骨质。这些动物循环中的免疫反应性PTH水平随年龄增长而升高,在27月龄时显著上升。第3组和第5组大鼠骨骼和血清PTH水平的年龄相关变化与第1组动物相似,只是第5组大鼠血清PTH没有出现末期升高。在食物限制时间最长的第2组和第4组动物中,骨骼生长和成熟减缓,但这些动物没有经历老年骨质流失或循环PTH的显著末期升高。因此,食物限制的有益效果并非特别归因于蛋白质摄入量的限制或仅在快速生长期间限制食物摄入量。