Free alpha subunit of the pituitary glycoprotein hormones. Measurement in serum and tissue of patients with pituitary tumors

A solid-phase radioimmunoassay was developed that measures the free alpha subunits of pituitary glycoprotein hormones (αPGpHs) and has negligible cross-reactivity with the intact hormones (<0.014% for thyroid-stimulating hormone [TSH], <0.1% for human chorionic gonadotropin [hCG], 0.8% for luteinizing hormone [LH], and 2.0% for follicle-stimulating hormone [FSH]). The assay is standardized with the alpha subunit of hCG but also reacts well with the alpha subunits of the other glycoprotein hormones (84% for αTSH, 77% for αFSH, and 64% for αLH). Concentrations as low as 0.3 μg/L can be reliably measured, and the 97.5% reference range in 27 healthy adults, including postmenopausal females, is ≤ 1.2 μg/L. Elevated preoperative αPGpH concentrations were found in 45 (9.4%) of 479 sera from patients with pituitary adenoma and 3 (4.5%) of 66 patients with nonadenomatous sellar lesions. Postoperative αPGpH levels were lower in 30 of 39 adenoma patients and 2 of 3 nonadenoma patients. In five (1%) of the patients with pituitary adenomas, αPGpH was the only elevated serum hormone marker. Serum values of αPGpH correlate weakly with alpha subunit immunocytochemical staining - 95% of those with negative staining have normal αPGpH values, but only 18% of those with positive staining have elevated αPGpH values.