Some unexpected effects of thyrotrophin on the metabolism of thyroid cells isolated from non-toxic goitre.

In cultured cells of normal dog thyroid thyrotrophin (TSH) has been shown to have a mitogenic effect. The present study suggests an opposite action in cells from human non-toxic goitre. After incubation of these cells with [3H]thymidine, a decreased incorporation into DNA is observed in the presence of TSH. Whereas in dog thyroid cells the hormone enhances the incorporation of [3H]leucine and [14C]glucosamine into macromolecules, TSH inhibits the incorporation by human non-toxic goitre cells. Polyacrylamide gel electrophoresis analysis of the proteins present in the cell layer or released in the culture medium shows that the inhibition affects all the newly synthesized peptides, including the radioactive material co-migrating with the major band (330 000 daltons) observed with human purified thyroglobulin. While several hydrolase activities are not influenced by TSH in dog thyroid cells, the hormone markedly decreases the activities of some hydrolases of thyroid cells from human non-toxic goitre. Our results therefore suggest that, in cultured thyroid cells from human non-toxic goitre, TSH induces a resting state of the cells, characterized by reduced growth, reduced protein synthesis and reduced thyroglobulin hydrolysis.