A Specific Radioimmunoassay for Human β-Lipotropin*

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Abstract
A homologous RIA for human β-Lipotropin (βhLPH) has been developed. At a final dilution of 1:24,000, the antiserum employed shows cross-reaction with βhLPH but none with human β-MSH (βhMSH), and it is concluded that the antigenic determinant lies within the N-terminal 1-36 region of βhLPH. With extraction of 3-ml plasma samples, the assay is sufficiently sensitive to measure circulating βhLPH levels in normal individuals at 0900 h (25–200 pg/ml). There is a circadian variation with levels falling to (<20–80 pg/ml) at 2300 h. βhLPH levels rise after metyrapone and after insulin-induced hypoglycemia, and fall after administration of dexamethasone. In patients with a variety of diseases of the pituitary-adrenal axis, levels of βhLPH follow immunoreactive ACTH levels, although the two are not always secreted on a 1:1 molar basis.