Assessment of the bioactivity of human and bovine thyrotrophin preparations using a porcine thyroid cell bioassay.

The biopotency of six preparations of thyrotrophin (TSH) has been compared in a highly sensitive in vitro porcine thyroid cell bioassay using iodide uptake as an endpoint. Three of these preparations were of human origin and three derived from bovine pituitary tissue. One human TSH preparation, the 2nd International Reference Preparation, 80/558, was used to calibrate the other five. The log dose-log response curves for all preparations were sigmoidal in shape. For the purpose of evaluation the central linear portions of the curves were compared. With all preparations the slopes in this region were very similar. The relative biopotencies of the bovine preparations (unit:unit) were at least five times those of the human standards when measured using the porcine thyroid cell bioassay. These findings emphasise the need to control the TSH standards employed in a variety of bioassays, particularly those used for between-laboratory comparison.