LATS-protector activity in thyrotoxicosis measured by thyroidal intracellular colloid droplet formation.

A modified assay method of LATS and LATS protector (LATSP) was devised employing murine thyroidal intracellular colloid droplet formation. This method is 4- to 8-fold more sensitive to stimulators than is the regular McKenzie bioassay. For the assay of LATSP, IgG to be tested was incubated with human thyroid homogenate, then LATS-IgG was added and it was further incubated. The potency of LATS in the mixture was assayed. The adequacy of the present method for the assay of LATSP was supported by the facts that the LATSP activity was roughly related to the dose of IgG tested and that the inactivation of LATSP was observed when the IgG was pretreated with human thyroid particulate fraction and then assayed. With this method, 7 out of 32 patients with thyrotoxicosis showed LATS and 18 showed LATSP. Changes in LATSP were followed up in 7 cases out of the 18. LATSP activity decreased and then disappeared in 6 out of the 7 cases, when they had been euthyroid for a certain period of time. At 12-20 months after the treatment either by thionamide medication or by subtotal thyroidectomy. LATSP and 131I-thyroid uptake were measured in these 6 patients. In all of the 6, LATSP was negative regardless of thyroid suppressibility.