Effects of Streptozotocin-induced Diabetes Mellitus on Hypothalamic-Pituitary-Thyroid Axis in Rats

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The effects of streptozotocin-induced diabetes mellitus on the hypothalamic-pituitarythyroid axis in rats were studied. Streptozotocin (60mg/kg) was injected ip. Rats were decapitated at two and four weeks after the streptozotocin treatment. Thyrotropin releasing hormone (TRH), thyrotropin (TSH), thyroxine (T4), 3, 3, 5-triiodothyronine (T3), 3, 3, 5-triiodothyronine (rT3), 3, 3-diiodothyronine (3, 3-T2) and 3, 5-diiodothyronine (3, 5-T2) were measured by means of the specific radioimmunoassay for each. Immunoreactive TRH (ir-TRH) contents in the hypothalamus significantly decreased at four weeks (p<0.02). Basal TSH levels in plasma significantly decreased (p<0.005, p<0.001), and plasma ir-TRH and TSH responses to cold were significantly inhibited after the strepotozotocin treatment (p<0.001). The plasma TSH response to TRH was decreased, but not significantly. The plasma T4 and T3 levels fell significantly. RT3 did not change throughout the experiment. 3, 3-T2 levels in plasma fell significantly, whereas 3, 5-T2 increased. Blood glucose levels rose significantly after streptozotocin treatment, but insulin treatment led to partial restoration. The findings suggest that streptozotocin-induced diabetes mellitus affects various sites of the hypothalamic-pituitary-thyroid axis in rats.
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