Autoradiographic thyroid evaluation in short-term experimental diabetes mellitus

Abstract

Previous studies have shown that in vitro thyroid peroxidase (TPO) iodide oxidation activity is decreased and thyroid T4-5'-deiodinase activity is increased 15 days after induction of experimental diabetes mellitus (DM). In the present study we used thyroid histoautoradiography, an indirect assay of in vivo TPO activity, to determine the possible parallelism between the in vitro and in vivo changes induced by experimental DM. DM was induced in male Wistar rats (about 250 g body weight) by a single ip streptozotocin injection (45 mg/kg), while control (C) animals received a single injection of the vehicle. Seven and 30 days after diabetes induction, each diabetic and control animal was given ip a tracer dose of 125 I (2 µCi), 2.5 h before thyroid excision. The glands were counted, weighed, fixed in Bouin's solution, embedded in paraffin and cut. The sections were stained with HE and exposed to NTB-2 emulsion (Kodak). The autohistograms were developed and the quantitative distribution of silver grains was evaluated with a computerized image analyzer system. Thyroid radioiodine uptake was significantly decreased only after 30 days of DM (C: 0.38 ± 0.05 vs DM: 0.20 ± 0.04%/mg thyroid, P<0.05) while in vivo TPO activity was significantly decreased 7 and 30 days after DM induction (C: 5.3 and 4.5 grains/100 µm 2 vs DM: 2.9 and 1.6 grains/100 µm 2 , respectively, P<0.05 ). These data suggest that insulin deficiency first reduces in vivo TPO activity during short-term experimental diabetes mellitus.

The Influence of Intranasal Insulin on Hypothalamic-Pituitary-Thyroid Axis in Normal and Diabetic Rats

“…The results of our experiments on rats with acute DM1 are consistent with these findings by other authors. A reduced production of thyroid hormones may be the result of thyroid cells' resistance to TSH [12,32,33], which is due, primarily, to the weakening of TSH receptor sensitivity to TSH in thyrocytes and the changes in TSH-regulated intracellular signaling cascades. Earlier we have shown that in the thyroid gland of rats with acute DM1 the TSH-induced stimulation of adenylate cyclase activity was reduced [18,34].…”