Mallinckrodt, Inc.

Joel Glovsky

James L Brown

A radioimmunoassay method for the in vitro determination of the renin activity of an unknown plasma sample. In this method an unknown generation sample is provided by mixing the unknown plasma sample with a generation buffer solution and an inhibitor for enzymes which convert angiotensin I to other substances. The unknown generation sample is incubated to generate angiotensin I therein by action of renin upon angiotensinogen, thereby producing a generated unknown sample. A generated unknown radioimmunoassay reaction mixture is provided by mixing the generated unknown plasma sample with a predetermined amount of radioactively labeled angiotensin I, a predetermined amount of an antibody for angiotensin I, and an amount of an assay buffer solution sufficient to provide in the unknown reaction mixture renin and angiotensinogen concentrations at which there is no substantial angiotensin I generation at the temperatures to which the generated unknown radioimmunoassay reaction mixture is subsequently exposed. The reaction mixture is incubated at a temperature of at least about 12.degree.C. so that a competitive binding reaction takes place between the antibody and both labeled and unlabeled angiotensin I. Bound angiotensin I is separated from unbound angiotensin I and the relative proportions of bound and unbound labeled angiotensin I in the reaction mixture are determined. The angiotensin I content of the generated unknown reaction mixture is determined by comparison of the relative proportions of bound and unbound labeled angiotensin I in the reaction mixture with the relative proportions of bound and unbound labeled angiotensin I in standard radioimmunoassay reaction mixtures containing known amounts of unlabeled angiotensin I. The renin activity of the plasma is determined from the difference between the angiotensin I content of the generated unknown reaction mixture and the angiotensin I content of an ungenerated radioimmunoassay reaction mixture containing a sample of the same unknown plasma. A kit useful in carrying out the method of the invention is also disclosed.

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Fenton, MO, United States of America

Joel Glovsky