AUTORADIOGRAPHIC THYROID EVALUATION IN SHORT-TERM EXPERIMENTAL DIABETES-MELLITUS

Previous studies have shown that in vitro thyroid peroxidase (TPO) iod ide oxidation activity is decreased and thyroid T4-5'-deiodinase activ ity is increased 15 days after induction of experimental diabetes mell itus (DM). In the present study we used thyroid histoautoradiography, an indirect assay of in vivo TPO activity, to determine the possible p arallelism between the in vitro and in vivo changes induced by experim ental 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 I-125 (2 mu Ci), 2.5 h before thyroid excision. Th e glands were counted, weighed, fixed in Bouin's solution, embedded in paraffin and cut. The sections were stained with HE and exposed to NT B-2 emulsion (Kodak). The autohistograms were developed and the quanti tative distribution of silver grains was evaluated with a computerized image analyzer system. Thyroid radioiodine uptake was significantly d ecreased 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 d ecreased 7 and 30 days after DM induction (C: 5.3 and 4.5 grains/100 m u m(2) vs DM: 2.9 and 1.6 grains/100 mu m(2), respectively, P<0.05). T hese data suggest that insulin deficiency first reduces in vivo TPO ac tivity during short-term experimental diabetes mellitus.