Purification of tilapia thyrotropin from a crude pituitary homogenate by immunoaffinity chromatography using a matrix of antibodies against porcine follicle-stimulating hormone.

An immunoadsorbent matrix using antibodies against porcine follicle-stimulating hormone (pFSH), a high heterothyrotropic stimulant in tilapia, was used to purify tilapia thyrotropic hormone (t-TSH) from crude pituitary extracts. A homologous bioassay monitored TSH bioactivity during the purification. Thyroid hormones (thyroxine, T4; triiodothyronine, T3; and reverse triiodothyronine, rT3) and testosterone were measured in vivo in Tilapia nilotica. TSH activity eluted as one major peak at pH 2.8 using a PBS-glycine buffer. The TSH fraction increased plasma T4 and plasma rT3. The potency of tTSH was comparable to that of pituitary extract or its Con A II fraction; however, pFSH was a stronger thyroid stimulant. tTSH had no effect on plasma T3 levels and was free of gonadotropic activity, as indicated by its failure to alter plasma testosterone concentrations. Chromatographic and electrophoretic analyses demonstrated a high degree of purity. Like other vertebrate TSHs, the tTSH appeared to have a subunit structure with a possible microgeneity in one subunit.