Thyroidal Iodine Metabolism in Inbred and F₁ Hybrid Mice

¹ From the Roscoe B. Jackson Memorial Laboratory, Bar Harbor, Maine and the Department of Physiology and Pharmacology, Michigan State University, East Lansing, Michigan

Thyroidal iodine metabolism was studied in four inbred strains of mice and two groups of F₁ hybrids by use of radioiodine. Significant strain differences were found in both the 48-hour thyroidal retention of I¹³¹ and its output rate constant. Three closely related groups studied were C57BL/6, C57BR/cd and BBF₁, their F₁ hybrid. The other three groups included A/Jax, BALB/c and CAF₁, their F₁ hybrid. C57BL/6 mice had a significantly faster output rate and lower 48-hour I¹³¹ retention than any other group. The first three groups listed had a more rapid output rate and lower 48-hour retention than the last three. In intergroup comparisons and inverse relationship between I¹³¹ output rate and 48-hour retention was clearly shown. The results indicate that in mice pituitary TSH output, as indicated by thyroidal I¹³¹ output rate and thyroidal iodine pool size, is controlled by separate genetic factors.