Metabolism of Collagen in Experimental Hyperthyroidism and Hypothyroidism in the Rat1

Abstract

The metabolism of collagen was studied by injecting proline-14C into rats and determining the specific activities and total activities of hydroxy-proline-14C in the collagen fractions of the skin and in the urine, (a) When proline-14C was injected into thyroxine-treated rats, the total activity of hydroxyproline-14C in the collagen fractions of the skin was lower in the thyroxine-treated rats than in the controls. The total activity of hydroxyproline-14C in the urine was higher in the thyroxine-treated rats than in the controls. (b) When proline-14C was injected 30 days before the start of thyroxine injections, the administration of thyroxine caused an increase in the total activity of hydroxyproline-14C in the urine compared to the controls, (c) When proline-14C was injected into rats made previously hypothyroid by 2 131I injections, the total activity of hydroxyproline-14C in the soluble collagen of the skin and in the total collagen of bone was lower in the hypothyroid rats than in the controls. The total activity of hydroxyproline-14C was injected before the induction of hypothyroidism, there was first a period in which the urinary excretion of hydroxyproline was lower and the specific activity of urinary hydroxyproline-14C was higher in the hypothyroid rats than in the controls, but the total activity of urinary hydroxyproline-14C was similar in both groups. After this period the total activity decreased in the hypothyroid rats to one third of that in the controls. The results of the present study suggest that the rate of collagen synthesis is decreased both in hyperthyroidism and in hypothyroidism. In addition, hyperthyroidism is accompanied by increased rates of catabolism of both soluble collagen and insoluble collagen, and hypothyroidism is accompanied by decreased rates of catabolism of these forms of collagen.