A mechanism for the increased activity of α-amylase in serum upon radiation exposure

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α-amylase (EC.3.2.1.1) catalyzes the specific cleavage of α-1.4 glucan bonds in polysaccharides such as starch. α-amylase is produced by the pancreas (P-amylase) and the salivary glands (S-amylase). Stresses including radiation and major surgery are known to increase the levels of α-amylase in serum. Moreover, increased levels of α-amylase were observed in workers who were exposed to high-dose radiation in the Tokai-mura criticality accident, and they developed a painful bilateral swelling of the parotid glands. However, the mechanism is not fully understood. In this study, we examined mechanisms for the increased level and activity of α-amylase in blood by radiation exposure. Irradiation with doses of 3.5 to 14 Gy increased α-amylase activity in C3H/He mouse plasma in dose-dependent manner. A maximal level of α-amylase was observed at 12 h after irradiation (about 3-fold), and after that, level of α-amylase was decreased to about 2-fold at 24 h compared with that of control mouse plas … More ma. Non-denatured polyacrylamide gel fractionation of the plasma followed by starch-iodine staining showed that S-amylase was dominant in the increased activity by irradiation and P-amylase was not affected. On the other hand, irradiation inhibited increase in the flow rate of saliva induced by pilocarpine and decreased the α-amylase activity in saliva. Furthermore ligation of parotid-duct resulted in the increased α-amylase activity to about 3-fold in blood. We tested whether irradiation increases the production of α-amylase in a human salivary gland cell line HSY by western blot analysis and RT-PCR. When the HSY cells cultured on Matrigel, these cells differentiated into more mature cells ; they formed acinar structure. Irradiation failed to increase the activity or the mRNA level of α-amylase in these HSY cells. We prepared acinar cells from the parotid glands of mice and cultured them in vitro. Irradiation decreased the α-amylase activity in these primarily cultured cells and increased the activity in the culture supernatants. Irradiation did not affect apoptosis. Microscope images of cells stained with anti-amylase antibody showed that irradiation decreased the fluorescence intensities. Furthermore, horseradish peroxidase (HRP) was administered retrogradely as a tracer via a main excretory duct of parotid gland in a rat. The tracer was present in cells from an irradiated rat but not in a control rat. When HRP was injected intravenously, the tight junction prevented the passage of tracer from acinar lumina and intracellular canaliculi into the intercellular space in a control rat. However, the tracer was detected in an irradiated rat. Our results suggest that irradiation may cause increased levels of α-amylase in blood by not altering its production but affecting barrier function of tight junction ; amylase is released into blood vessels through distracted barrier by irradiation. Less