Does-related effect of growth hormone on thyroidal radioiodine uptake

Even though growth hormone was reported to play a role in mammalian calorigenesis, few studies have examined its effect on thyroid function. Consequently, the modulatory effect of bovine growth hormone (BGH) on thyroid incorporation of 131I was studied in hypophysectomized (H) rats. Not surprisingly, H recipients fed a low iodine diet consistently displayed greater thyroidal uptakes of radioactive iodine than recipients given regular diets. Furthermore, thyroid radioactive counts increased predictably in direct proportion to the quantity of bovine thyrotropin administered. Larger doses of BGH suppressed the thyroidal uptake of 131I whereas smaller doses either had no effect or enhanced thyroidal activity. Thus, these results affirm that radiolabelled and non-radiolabelled iodine compete in thyroid metabolic processes and furthermore demonstrate that high doses of BGH inhibit thyroid activity.