Thyroactive Iodinated Protein in Protein-Depletion of Rats for Use in Protein Assays

Abstract

Since the development by Cannon and his associates ( 1 , 2 ), of the use of the hypoproteinemic rat in studies on the dietary utilization of proteins and of amino acids, the general technic has been employed in many laboratories for assaying the plasma protein-regenerating ability of proteins and of amino acid mixtures. However, the method has the disadvantage that a relatively long time, usually about 3 months, is required for the preparation of the animals for purposes of assay. In view of the accelerating effects of thyroid hormone on protein metabolism, which have been well described by various investigators( 3 ), the feeding of one of the thyroactive substances, such as an iodinated protein, would appear to be a useful means of speeding up the depletion process in the preparation of test rats. Data presented here were obtained from some preliminary and exploratory trials made to test this possibility and indicate that the use of iodinated casein for this purpose is practical.

Observations were made on the changes in plasma proteins in rats fed for different periods of time on a basal low-protein diet and in rats fed the same basal diet supplemented with 0.1% and 0.15% of iodinated casein.∗ Further observations were made after a period of repletion, on one of the groups of animals which had been depleted with iodinated casein. Male albino rats of approximately 200 g weight were used in all groups. The animals were housed individually and fed the diets ad libitum. The diets used are indicated in Table I. The iodinated casein added to diets 2 and 3 was mixed directly with the other ingredients. Blood samples of 0.3 to 0.4 ml amounts were obtained from the rats by heart puncture and mixed with a small amount of purified heparin.