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.