Evaluation of a sensitive, in vitro bioassay for chicken thyroid stimulating hormone using FRTL-5 cells, a rat thyroid cell line.

An in vitro bioassay for mammalian thyroid stimulating hormone (TSH) based on TSH-induced cyclic adenosine 3',5'-monophosphate (cAMP) production in FRTL-5 cells, a rat thyroid cell line, was used to measure chicken TSH. The addition of chicken pituitary homogenate equivalent to > or = 25% of a chicken pituitary gland to cultured FRTL-5 cells increased cAMP within these cells in a dose-dependent manner. The glycoprotein fraction derived from the pituitary homogenate was further fractionated by isoelectric focusing within a pH range of 5 to 11. Analysis of the focused fractions by the bioassay detected three major components with isoelectric points of 9.30, 7.12, and 3.82, in addition to several minor ones distributed over a wide range of pH, from alkaline to acidic. The isoelectric focusing profile obtained by the bioassay was clearly different from those obtained by radioimmunoassay for chicken LH and radioreceptor assay for chicken FSH, indicating that fractions contained chicken TSH. The homogenate of the cephalic portion of the chicken anterior pituitary gland was 4.46 times more active than that of the caudal portion in the bioassay, which is consistent with previous findings on localization of TSH in the chicken pituitary. We conclude that the bioassay using FRTL-5 rat thyroid cells is a sensitive, specific, and time-saving method of measuring chicken TSH.