Hyperthyroidism Induced by Thyrotropin-Releasing Hormone in Mice

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Abstract
To test whether repeated administration of thyrotropin—releasing hormone (TRH) results in hyperthyroidism, we administered TRH, 1 μg every 12 hr, to 6 groups of mice for 1–10 days. No increase in thyroid size, 131I uptake or serum T4 was noted in any group of animals when compared to saline injected controls. When the experiment was repeated with a higher dose, 10 ¼g of TRH, hyperthyroidism evidenced by a mild increase in serum T4 was detected only after 2 doses of TRH; it was not present in any other group despite continued administration of TRH at 12–hr intervals for up to 7 days. In another experiment, where TRH (10 ¼g) was administered at 2–hr intervals around the clock for 1–10 doses, serum T4 increased after the first dose and the increment was maintained at comparable or higher levels during subsequent injections. Thyroid 131I uptake and thyroid size were not significantly affected after 1–5 doses of TRH; however, significant increase in both was noted after administration of 10 doses. These results with TRH were quite comparable to those obtained with equipotent doses of TSH. These studies indicate that sustained hyperthyroidism can be induced by a large dose of TRH administered at appropriate intervals.(Endocrinology92: 1731, 1973)

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