cytochalasin-b and Hyperthyroidism

Hyperactive dog thyroids were prepared by repeated TSH stimulation in vivo. Butanol extractable 125iodine (BE 125I) release in vitro from such hyperactive thyroid slices was enhanced when compared with resting slices. Apical pseudopods an colloid droplets were exceptional in such hyperactive thyroids. Moreover, BE125I release was intensitive to cytochalasin B, microtubules and metabolic inhibitors, and decreased only with temperature. Our data demonstrate that hormonal secretion by hyperactive thyroids is not secondary to apical phagocytosis of colloid droplets.

Topics: Animals; Cytochalasin B; Dogs; Hyperthyroidism; In Vitro Techniques; Iodine Radioisotopes; Temperature; Thyroid Gland; Thyrotropin

Hyperactive dog thyroids were prepared by repeated TSH stimulation in vivo. Butanol-extractable 125I (BE125I) release in vitro from slices and hormonal secretion in vivo in the thyroid vein was enhanced. Apical pseudopods and colloid droplets were very infrequent in such hyperactive thyroids. Moreover, BE125I release was insensitive to cytochalasin B, to inhibitors of microtubules, and to metabolic inhibitors, and decreased only with temperature. Our data demonstrate that hormonal secretion by hyperactive thyroids is not secondary to apical phagocytosis (i.e. macropinocytosis). Micropinocytosis or intraluminal hydrolysis of thyroglobulin are suggested as first step of the secretory process.

Topics: Animals; Cytochalasin B; Dogs; Hyperthyroidism; Iodides; Phagocytosis; Temperature; Thyroid Gland; Thyrotropin