Evidence that both long-acting thyroid stimulator and long-acting thyroid stimulator-protector stimulate the human thyroid gland.

Thyroid-stimulating immunoglobulins were prepared from two potent sera, one contained long-acting thyroid stimulator (LATS) and the other contained both LATS and LATS-protector (LATS-P). The potencies of the immunoglobulin G (IgG) preparations were estimated in the McKenzie assay. The accumulation of cyclic AMP in mouse thyroid lobes was stimulated only by LATS--IgG; LATS-P--IgG was inactive. In contrast, both LATS-IgG and LATS-P--IgG were equally effective in slices of human thyroid.