The specificity and application of a radioimmunoassay for the alpha-subunit of luteinizing hormone in man.

A sensitive radioimmunoassay for the alpha-subunit of LH has been developed. Differences in the immunopotency of LH, FSH, and subunit preparations were found and are described in detail. The assay has been applied to the measurement of circulating levels of alpha-subunit; higher levels of alpha-subunit were found in post-menopausal than in pre-menopausal women, or men, and a rise in alpha-subunit was seen after LH-RH but not TRH administration. Elevated levels of free alpha-subunit were found in foetal cord blood at term. These results suggest that the alpha-subunit circulates independently of the intact pituitary and placental glycoprotein hormones.