Protein and Nucleic Acid Content of the Thyroid Glands of Different Mammals

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Abstract
Standard methods for measuring the RNA and DNA in tissues were applied to analysis of the thyroid gland. The presence of thyroglobulin gave rise to certain errors not encountered in other mammalian tissues, and modified analytical procedures were therefore devised. With increasing size of mammals, the concentration of protein in the thyroid gland increases, whereas there is a diminution in the concentration of RNA and, to a smaller extent, of DNA and phospholipid. These findings can be correlated with an increase in follicle size in larger mammals, which results in more colloid in proportion to the number of cells. Calculations made from the data show that the amount of protein in the thyroid glands of various mammals is maintained at a constant proportion of body weight. However, the number of cells in the thyroid gland does not increase in parallel with the size of the species, and the larger mammals also have less RNA per cell. This last finding suggests that the turnover of protein in the thyroid glands of larger mammals is less rapid than in smaller mammals. (Endocrinology76:171,1965)