Charles H. Barrows

Renal clearance of intravenously administered vitamin B12.

Summary The erythropoietic stimulating principle present in the filtrate of plasma obtained from anemic rabbits was partially purified by ethanol fractionation. This material was active in increasing Fe59 intake of normal rats and in producing a reticulocytosis and hematocrit elevation in repeatedly injected normal rats. Fe59 uptake was stimulated by as little as 0.08 mg of the fraction representing a concentration of 3,000 fold over that occurring in the plasma.

Fractionation of radioactive B12-complex in kidney homogenates.

Summary The amount of radioactive B12 bound by substances in kidneys of rats pre-injected with this radiovitamin was found to be approximately one-half to two-thirds of the total radioactivity by 4 independent procedures. The amounts of radioactivity in the 3 fractions obtained by differential centrifugation were also determined with only a small portion in the mitochondria. Relative percentages of the radioactivity in these 3 components remained essentially unchanged as a result of pre-injection of unlabeled B12.

Dietary Restriction and Biologic Variables

Dietary restriction has been shown to increase the life span of a variety of young growing laboratory animals (1). For example, this phenomenon has been reported in the following model systems: Tokophrya, Campanularia flexuosa, Daphnia sp., rotifers, Drosophila sp., and fish. In addition, a number of laboratory experiments have been carried out on rodents. It has been generally believed that nutritional manipulations that increase life span had to be imposed during early growth. This concept originated from the early work of Minot, who postulated that senescence follows the cessation of growth (2,3). Furthermore, Lansing indicated that aging in the rotifer involved the appearance of a cytoplasmic factor that coincided with the cessation of growth (4). However, recent studies have indicated that dietary restriction imposed in adult life was effective in increasing the life span of rotifers, Daphnia sp., rats, hamsters, and mice (11). In studies using both young growing and adult animals, dietary restriction has been brought about by: (a) reducing the daily dietary intake of a nutritionally adequate diet (one that supports maximal growth); (b) intermittently feeding a nutritionally adequate diet (eg, feeding every second, third, or fourth day); and (c) feeding ad libitum a diet containing insufficient amounts of protein to support maximal growth.