Fate of circulating isoamylases in the rabbit

Amylase purified from the pancreas and parotid gland of rabbits was labeled with ¹²⁵I. Plasma disappearance was biexponential after bolus injection. Half-time of metabolic clearance was 97 and 95 min, respectively, for pancreatic and salivary ¹²⁵I-amylase. About 20 and 30% of the injected pancreatic and salivary ¹²⁵I-amylase, respectively, appeared intact in the urine within 24 h. Organs were assayed for radioactivity at specified times. No organ at any time contained more than 20% of injected radioactivity. At 24 h, more than 90% of radioactivity in organs was acid soluble. Bilateral nephrectomy significantly slowed plasma disappearance, although 90% hepatectomy did not. These studies in the rabbit indicate that 1) homologous isoamylases are cleared from plasma at rates comparable with those reported in primates; 2) in contrast to primates, urinary excretion of salivary amylase is greater than pancreatic amylase; and 3) within 24 h, virtually all of injected ¹²⁵I-labeled isoamylases were catabolized or excreted.