Radioimmunoassay for human salivary amylase

A radioimmunoassay (RIA) for human salivary amylase was developed. Human salivary amylase was purified from parotid saliva by a combination of Sephadex gel filtration and cation exchange chromatography. Purified salivary amylase was used both as the standard antigen and for the generation of ¹²⁵I-labeled amylase. Antibody to salivary amylase was raised in New Zealand white rabbits and used in a nonequilibrium double-antibody procedure for the RIA. The RIA was sensitive (10 ng/ml) and specific, displaying a limited cross-reactivity for pancreatic amylase (1%, $\text{w}\text{w}$). Analysis of patient sera by RIA shows that salivary amylase constitutes approximately 60% of the total serum amylase, that the salivary amylase found in the serum of patients with Sjögren's syndrome and macroamylasemia is immunologically indistinguishable from that of normal persons, and that salivary amylase can be evaluated by RIA in the serum of patients with pancreatitis.