In Vitro Thyrotropin-Induced Proteolysis in the Thyroid Gland*

Abstract

Numerous studies, both in vivo and in vitro, have been designed to define the biochemical events influenced by the action of thyrotropin (TSH) on the thyroid gland. In vivo experiments have shown that this hormone stimulates growth of the follicular epithelium, trapping of inorganic iodide, biosynthesis of hormonal iodine, turnover of thyroglobulin, and release of inorganic iodide and hormonal iodine. The latter action has received much attention because of its relevance to the concentration of circulating thyroid hormone and because of the promptness of this response in vivo. De Robertis demonstrated an increase in intrafollicular proteolytic activity after administration of TSH to rats (1). Keating, Rawson, Peacock, and Evans (2) noted loss of radioiodine from the chick thyroid after TSH administration. Similar results have been observed in other laboratory animals (3, 4). The administration of TSH to euthyroid humans also results in prompt release of radioiodine from the thyroid (5-7), occurring 90 minutes after intramuscular inj ection in one study (7).In vitro techniques have permitted investigation in a more rigidly controlled environment. Such observations on the effect of TSH added to thyroid tissue have confirmed the stimulus to the trapping of iodide (8, 9). TSH in vitro has also been shown to enhance certain parameters of intermediary metabolism such as carbon-1 oxidation of glucose (10, 11), phospholipid synthesis (12), oxygen consumption, lipogenesis from labeled glucose, incorporation of inositol into phospholipid (13), and the level of triphosphopyridine nucleotide (14). Few

Hormone‐induced modifications of free tyrosine in the rat thyroid gland

“…The present experiments differ from those of Granner et al (1962Granner et al ( , 1963 and Poffenbarger et at. (1963) in that the effect of T 4 was evaluated in hypophysectomized animals.…”

“…There is evidence in this study, as in those of Halmi, Granner, Albert & Doughman (1959), Khazin & Reichlin (1961) and Granner, Curtis, Scranton & Halmi (1962, that thyroid hormones may have an effect on thyroid gland function beyond their ability simply to inhibit release of TSH. The present experiments differ from those of Granner et al (1962Granner et al ( , 1963 and Poffenbarger et at. (1963) in that the effect of T 4 was evaluated in hypophysectomized animals.…”

“…Following treatment with thyroxine for various periods there was a significant fall both in thyroid weight and in free tyrosine concentration in the gland. Treatment with TSH is known to increase gland weight and uptake of 14C tyrosine (Klitgaard, Palay & Meade, 1963;Poffenbarger, Powell & Deiss, 1963;Raghupathy, Tong & Chaikoff, 1963). In addition, TSH may also stimulate the rate of the deiodination of intraglandular iodotyrosines.…”

Reduced Acid Protease Activity In Vitro of Lysosomes from Thyroid Gland of Rats Chronically Treated with Propylthiouracil and Perchlorate

“…Lysosomal hydrolases of the thyroid gland represent a complex of different enzymes which play a maj or role in the intrathyroidal digestion of thyroglobulin decomposing its compound glycoprotein structure (Wollman, 1969;Van den Hove-Vandenbroucke, 1980). Optimal activity of thyroid intralysosomal proteases is shown at low pH values (Alpers et al, 1955;Poffenbarger et al, 1963;Jablonski and McQuillan, 1967;Ahn and Rosenberg, 1967;Smith et al, 1969;Peake et al,, 1970;Pisarev and Altschuler, 1973;Itikawa and Kawada, 1974). However, their pH maximum depends on the origin of thyroid lysosomes, i.e.…”