Abstract
The development of a specific ovine thyrotropin (oTSH) radioimmunoassay from non-specific antisera is described. Initial antisera produced in rabbits against NIH-TSH-S6 was found to cross react with ovine luteinizing hormone (oLH) and ovine follicle stimulating hormone (oFSH). Three methods were used to increase the specificity of the oTSH radioimmunoassay: (1) Immunoadsorption of the antisera on Sepharose®; (2) Preadsorption of the antisera with oLH and oFSH; and (3) Radioiodination of the ß-subunit of bovine TSH. All three methods resulted in improved specificity of the assay systems for oTSH. The increased specificity is demonstrated by: (1) The addition of oLH, oFSH, oGH and dilutions of plasma caused inhibition of 125I-bTSH in a manner which was parallel to that of the NIH-TSH-S6 reference standard; (2) Bioassay/ radioimmunoassay ratios of TSH activity in NIH-LH-S16 and NIH-FSH-S8 were 0.84 and 1.00, 0.96 and 0.75, and 1.02 and 1.50 for the immunoadsorption, preadsorption and 125I-β-TSH systems, respectively. As a measure of accuracy of each system, recovery curves were determined with each system. Recovery lines for the three systems had correlation coefficients of 0.999, 0.997, 0.978, intercepts of 0.19, –.70, 0.29 and slopes of 0.93,1.28,0.74, respectively, for the immunoadsorption, preadsorption and 125I-β-TSH systems. Plasma levels of oTSH in castrate (6.8 ng/ml) and lactating (6.7 ng/ml) ewes were significantly greater (P< .01) than for cyclic (4.3 ng/ml) or pregnant (4.0 ng/ml) ewes using this assay system. Plasma levels of oTSH in lambs were significantly (P< .01) elevated following thyroidectomy (117 vs. 0.8 ng/ml). These data demonstrate the utility of these methods of improving assay specificity when antisera have been demonstrated to be non-specific. Copyright © 1974. American Society of Animal Science . Copyright 1974 by American Society of Animal Science.