T3 release from thyroid slices as an assay for thyroid stimulators.

A new in vitro bioassay for thyroid stimulators is described. The method is based on radioimmunological measurement of triiodothyronine (T3) release from thyroid slices. Small thyroid slices were cut from several porcine thyroids. The slices were pooled in incubation vessels. The stimulating effect of human thyroid-stimulating hormone (TSH), bovine TSH, and serum from a patient with Grave's disease was investigated. After 3 hr the T3 concentration was significantly higher in the vessels containing the thyroid stimulators than in the control vessels. For maximal sensitivity 16 hr of incubation was used in the assay. Bovine TSH, human TSH, and serum from a patient with Grave's disease gave linear dose response curves in a log-log system. For bovine TSH the curve was linear from 5 to 125 muU/ml incubation medium. The dilution curves for bovine TSH and serum from a patient with Grave's disease were parallel. The dilution curve for human TSH was considerably steeper. In 5 assays the lambda values for the bovine TSH curves were 0.10-0.16 (mean, 0.12). In 3 assays the lambda values for the human TSH curves were 0.05-0.07.