A specific radioimmunoassay for human beta-lipotropin

A homologous RIA for human beta-lipotropin (beta hLPH) has been developed. At a final dilution of 1:24,000, the antiserum employed shows cross-reaction with beta hLPH but none with human beta-MSH (beta hMSH), and it is concluded that the antigenic determinant lies within the N-terminal 1-36 region of beta hLPH. With extraction of 3-ml plasma samples, the assay is sufficiently sensitive to measure circulating beta hLPH levels in normal individuals at 0900 h (25-200 pg/ml). There is a circadian variation with levels falling to (less than 20-80 pg/ml) at 2300 h. beta hLPH 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 beta hLPH follow immunoreactive ACTH levels, although the two are not always secreted on a 1:1 molar basis.