[Radioimmunological system for the quantitative determination of progesterone in human blood serum].

A methodical approach to development of a radioimmune system for quantitative assay of progesterone in the blood serum of man is described. It implies investigation of every component in the system and conformity of these components by the physico-chemical properties and concentrations. An antiserum to the progesterone conjugate with bovine serum albumin was prepared. The "fitting density" of the heptaene was 35 mol/mol of the protein. The linkage with the carrier protein in it was performed by the functional group at C(ii) of the steroid molecule. The antiserum had a high titre (28000), high specificity and affinity to progesterone (Ka (3.5 +/- 0.4) X 10(9) M-1). The antiserum characteristics did not depend on the hydrogen ion concentration in the solution at pH 3.5-10.0 and the ionic strength of the buffer solutions (0.05 to 1.0 M). This allowed performing the radioimmunological assay at pH 3.5. Under such conditions complete inhibition of the endogenic binding proteins of the blood serum was possible. 125I preparations of progesterone made in the USSR were used in the study. The progesterones were prepared by adding the molecule of histamine containing the 125I atom to the molecule of progesterone modified at C(3). The quality of the 125I preparations of progesterone was estimated by their immune reactivity. The standard solutions of progesterone were prepared with the donor blood serum. It was shown that quantitative determination of progesterone in the blood serum at clinically significant ranges of the hormone concentration was possible at the final antiserum dilution of 1:28000, the label activity of 20000-30000 imp/min per a sample and the content of the blood serum in the analyzed sample equal to at least 10 per cent. A simple and reliable procedure for the assay of progesterone in the blood serum of man was developed.