A comparison of the bioactivity of human and bovine thyrotrophin preparations, as determined by intracellular cyclic AMP responses of cultured FRTL-5 cells and human thyroid cell monolayers

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Abstract
A clonal strain of TSH-dependent rat thyroid cells (FRTL-5) was used to evaluate the biological activity of reference preparations of both human and bovine TSH. Using the accumulation of intracellular cAMP as a response parameter, the widely used bovine TSH preparation, Armour ''Thytropar'', was calibrated against the First International Standard of Thyrotropin (pituitary TSH), bovine, for immunoassay. Log dose-log response curves were parallel, and a relative potency of 2.4 IU unit of ''Thytropar'' was obtained. Subcultures of FRTL-5 cells were more responsive to both bovine and human TSH than were human thyroid follicular cells maintained as primary monolayer cultures. Dose-response curves for cAMP accumulation were parallel for a single cell type differentially incubated with human TSH (the First International Reference Preparation) and bovine TSH (Armour ''Thytropar'') preparations. The relative potencies (units: IU) of bovine-human TSH were of the order of 2.0 when tested on both FRTL-5 cultures and primary human thyroid monolayers. The spectrum of structural differences between TSH receptors of different species, the discriminatory powers of the human and FRTL-5 cell TSH receptor are similar. FRTL-5 cells form the basis of a bioassay system of considerable value in the study of human thyroid stimulators, as was demonstrated in an evaluation of 2 recent preparations of human TSH.