In VitroEvidence for an Intracellular Mechanism Limiting the Thyroid Follicular Cell Growth Response to Thyrotropin

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Abstract
The mechanism that limits thyroid growth in the presence of a sustained elevation of serum TSH was investigated. An in vitro thyroid follicle culture was used, thyroid function and growth being assessed by 131I- organification and [3H]thymidine incorporation into DNA, respectively. Normal thyroid follicles incorporated [3H]thymidine in response to added TSH and also organified 11I-. Follicles taken from rats previously given goitrogen for 80 days, organified 131I-in response to added TSH but did not incorporate [3H]thymidine. These in vitro results parellel those obtained in in vivo studies despite the disruption of thyroid architecture. Apparently, the growth desensitization seen in vivo during sustained serum TSH elevation is mediated by an intracellular change in the follicular cell (either at the receptor or postreceptor levelL) rather than by a locally acting chalone.