Studies on the submaxillary gland. XIV. Radioimmunoassay of parotin

Abstract

In an effort to increase the sensitivity and specificity in the assay of salivary galnd hormones, a radioimmunoassay of parotin was attempted. The radioimmunoassy was carried out by incubation of a mixture of anti-parotin serum, 131I-parotin, and parotin sample, followed by separation of antibody-bound 131I-parotin (B) from free 131I-parotin (F) by paper electrophoresis with hydrodynamic flow. The radioactivity of B and F was counted, and the amount of parotin was determined by the ratio of B/F. The sensitivity was 2 mμg. Although S-parotin showed cross reaction with parotin to some extent, negative cross reactions were found for bovine serum γ-globulin and for other substances, such as the hypocalcemic substance from B. subtilis K and the MSH like substance from human which are active in decreasing calcium. This radioimmunoassay method can be used for determination of parotin present in the parotid gland, submaxillary gland, serum and urine of guinea pigs, and in urine and saliva of human, for which the previous methods of bioassay cannot be used directly. The present method confirmed that the content of the hormone in serum and urine of guinea pigs decreases suddenly after sialoadenectomy. The partial agreement between the results of the immunoassay of parotin and the bioassay is understandable from the fact that the anti-parotin serum neutralizes the hypocalcemic activity but not the leucocyte activity.