Defective thyroglobulin endocytosis and hydrolysis in thyroid cold nodules.

The catabolic phase of thyroid secretion has been studied by incubating thyroid slices with 0.1 % 125-I thyroglobulin (Tg) in the following cases: 11 follicular adenomas (FA), 8 hyerplastic nodules in multinodular glands (NM), 3 carcinomas (follicular or papillary, FC, PC) and normal (N) or micronodular tissue (M). Tg pinocytosis is severely impaired in all cold nodules (25 to 60 % reduction). In the follicular tumours (FA, FC), Tg hydrolysis is more affected than would be expected based only on reduced Tg endocytosis: the hydrolysis products remain in the phagolysosomes instead of being secreted. As far as the acid hydrolases are concerned these enzymatic activities are increased in nearly all nodules, in particular in follicular adenomas and carcinomas.