p019 : Growth Process in Rats is strictly associated with T3

Experimental and Clinical Endocrinology & Diabetes 2002 Thema: Poster Thyroid I

p019

Growth Process in Rats is strictly associated with T3

Boltze C^1,3, Brabant G², Dralle H³, Roessner A¹, Hoang-Vu C³

¹Dept. of Pathology, Otto-von-Guericke-University, Magdeburg; ²Dept. of Endocrinology, Medical School, Hannover; ³Dept. of General Surgery, Martin-Luther-University, Halle, Germany

The active thyroid hormone T3 influenced many metabolic processes, so leads hypothyreoidism to cretinism and hyperthyreoidism to rapid growth with delaying occlusion of epiphysial line of tube bones. Nutrition iodine is needed to synthesize thyroid hormones. Aim of our study was to show the effects of iodine deficiency, iodine excess and external radiation on the growth process in rats.

Male Han-SPRD rats (30 d old) were feed with a standard diet of 7000 ng iodine/100 g BW/d (C), or iodine deficient diet of 420 ng I-/100 g BW/d (LID) and standard diet with supplemented iodine in drinking water (72 000 ng l-/100 g BW/d; HID). A single external irradiation of the thyroid region (40 d) with a dose of 4 Gy (RA) was performed. Thyroid hormones, TSH and body weight were weekly measured. After 15, 35, 55 weeks animals from every group were killed and the thyroids glands were removed.

High iodine intake (HID) significantly stimulated TSH plasma levels twofold compared to C. T4 and T3 were not significantly changed in HID and C, whereas T4 clearly decreased about 80% and T3 about 52% in LID after 10 weeks. Growth process was finished in C after 18 in LID after 20 and in HID after 21 weeks, wit a BW of 500,6 g (C), 429.8 g (LID; -14%; p<0.01) and 474.9 g (HID). After radiation mean T3 and T4 plasma levels were not altered, whereas TSH levels were moderately increased in C and HID. In LID RA leads to an twofold increase of T3 after 10 weeks, T4 was not altered and TSH decreased about 48%. BW in C and HID showed no difference compared to the controls without RA. In LID BW increased to 475.6 g (+11%; p<0.01). Histological investigation showed in contrast to HID and C, that RA induced a complete destruction of follicle structure in LID after 15 weeks. The reparation process in these thyroids was finished not before 35 weeks. This phenomenon explains the increase of T3 in peripheral blood in LID after RA. These data provide evidence for an essential metabolical function of triiodothyronin and the important role of nutrition iodine in growth process.

Supported by: Deutsche Krebshilfe

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