Development of Glycoprotein Hormones and their α-and β-Subunits in Bovine Fetal Pituitary Glands. II. Quantitation of Free α- and β-Subunits by Radioimmunoassays and Correlation of Free α-Subunit with Thyrotropin, Follicle-Stimulating Hormone, and Luteinizing Hormone*

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Abstract
Homologous RIAs for bovine FSH-α and the β-subunits of bovine FSH, LH, and TSH have been developed. Antibody-bound tracer was separated by precipitating with a final concentration of 11% polyethylene glycol. The sensitivities of these immunoassays were 0.5–1 ng/ml for the purified subunits, and the precision was ±6% intraassay and ±11% interassay, as expressed by the coefficient of variation. In the RIA for bovine FSH-a, all the α-subunits of bovine FSH, LH, and TSH crossreacted identically on a weight basis and the intact hormones also cross-reacted identically with one another in a parallel manner to the α-subunits at a level of 10% cross-reactivity. In the immunoassays for bovine FSH-β, LH-β, and TSH-β, onlythe corresponding intact bovine FSH, LH, and TSH inhibited significantly at levels of 5%, 15%, and 25% cross-reactivities, respectively. To obtain the net values for the free α- and β-subunits in bovine fetal pituitary extracts, the amount of crossreactivity caused by different concentrations of intact FHS, LH, and TSH, as predetermined by radioligand receptor assays, was corrected for by subtracting it from the gross values of the subunits estimated by the specific RIAs. Free a-subunit was detected in bovine fetal pituitary glands at all stages of gestation. The pituitary content of free α-subunit increased gradually and proportionally with the fetal age. Higher content of pituitary 7alpha;-subunit was demonstrated in female fetuses at 3.75–5 and 5–6.25 months of gestation. However, the concentration of free 7alpha;-subunit remained relatively constant for both sexes throughout gestation. In spite of these variations, the ratios for α-subunit: total glycoprotein hormones were very similar for both male and female fetuses and decreased gradually in a similar manner throughout gestation. No free β-subunit of FSH, LH, or TSH was detected in bovine fetal pituitary glands.