Effects of streptozotocin-induced diabetes mellitus on hypothalamic-pituitary-thyroid axis in rats.

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Abstract
The effects of streptozotocin-induced diabetes mellitus on the hypothalamic-pituitary-thyroid axis in rats were studied. Streptozotocin (60 mg/kg) was injected i.p. Rats were decapitated at 2 and 4 wk after the streptozotocin treatment. TRH, 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 4 wk (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 streptozotocin 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; 3'',5''-T2 increased. Blood glucose levels rose significantly after streptozotocin treatment, but insulin treatment led to partial restoration. Apparently, streptozotocin-induced diabetes mellitus affects various sites of the hypothalamic-pituitary-thyroid axis in rats.