THYROID IODINE METABOLISM IN STREPTOZOTOCIN-DIABETIC RATS

Abstract

ABSTRACT Experiments have been performed to assess the effect of diabetes on thyroid function in male Wistar rats. Diabetes was induced by a single streptozotocin injection. As compared to normals, the diabetic rats displayed: 1) decreased rate of stable iodine uptake by the gland, as measured with a double isotopic technique; 2) decreased in vitro iodide uptake by the thyroid; 3) decreased T/S [I-] ratio after acute treatment with propylthiouracil; and 4) alteration in the distribution of labelled iodoamino acids in the gland. Furthermore, diabetic rats maintained lower plasma TSH levels than normals, in spite of the fact that plasma PBI concentration was slightly but consistently lower in diabetic than in normals, and that the pituitary TSH content was not affected by the lack of normal insulin levels. Injections of TSH (5 U/100 g body weight/day) for 5 days, into diabetic rats caused a return of thyroid function toward normal. Insulin administration resulted in an increase of thyroid weight, an increase of thyroid function, and an increase of pituitary TSH secretion in diabetic rats after the daily injection of 1, 2 or 3 U/100 g body weight/day for 7 days. The decreased pituitary TSH secretion in diabetic rats might involve a disturbance in the feed-back relationship between the thyroid and the pituitary, although other mechanisms could be involved.