Metabolism of human isoamylases in the rabbit

Human isoamylases were purified from pancreas and saliva with separation of salivary isoenzymes into glycosylated and nonglycosylated forms. After iodination, bolus injection of each purified isoamylase into conscious rabbits revealed biexponential disappearance from plasma. Glycosylated salivary amylase had a metabolic clearance (t 1/2 = 35 min) that was three to four times faster than nonglycosylated salivary (t 1/2 = 139 min) or pancreatic (t 1/2 = 111 min) amylase. In contrast to our previous studies on homologous (rabbit) isoamylases, human pancreatic isoamylase was excreted into urine as protein-bound radioactivity more readily than salivary isoamylase. No organ contained more than 18% of the injected dose of radioactivity except for a striking accumulation of radioactivity in the liver after injection of 125I-labeled glycosylated salivary amylase. We concluded that 1) human nonglycosylated salivary amylase and pancreatic amylase are cleared from the rabbit circulation at rates comparable with those reported for homologous isoamylases in the rabbit and baboon, 2) the rabbit kidney excretes human pancreatic amylase into urine more readily than human salivary isoamylases, and 3) with the notable exception of glycosylated salivary isoamylase, human isoamylases do not appear to be metabolized primarily by any single organ.