DEVELOPMENT AND APPLICATION OF MULTIPLE-RADIOIMMUNOASSAY (MULTI-RIA) FOR CIRCULATING HORMONES

Abstract

For simultaneous measurement of multiple hormones in blood samples from small experimental animals, multiple radioimmunoassay (Multi-RIA) was developed for rat pituitary hormones (LH, FSH, TSH, PRL, and GH) and epidermal growth factor (EGF) using double antibody method.
Parallel RIA, where ¹²⁵I-and ¹³¹I-labelled hormones were employed together, could measure 2 hormones at a time, and their assay values correlated well with those obtained by ordinary single assays. Smaller assay values were obtained with TSH, PRL, and GH. However, the lower slope of the regression line in TSH assay could be overcome by changing the anti-TSH serum for another batch of antiserum, indicating that this problem may be due to the antibodies used. Assay results of parallel RIA for female rat serum LH and FSH with samples obtained on proestrus day agreed well with those by single RIA.
Serial RIA, where 2 hormones were assayed successively, also produced assay values which correlated well with those from single assays. The lower binding of hormones in the second assay of serial RIA was improved by increasing the concentration of normal rabbit serum in the dilutant for the antiserum without affecting assay sensitivity.
Multi-RIA, which was developed by combining parallel RIA and serial RIA, could measure up to 4 hormones at a time. Application of multi-RIA to serum samples from castrated and cannulated male rats gave results which suggested synchronous secretion of LH, FSH, and PRL, indicating the usefulness of this assay method.