Abstract
We developed a method of radioimmunoassay and immunohistochemical technique to study the physiological action of somatostatin (SRIF) in the hypothalamus, the pancreas and the gastrointestinal tract. We obtained the antiserum following immunization with synthetic SRIF which had been conjugated with human a-globulin. Synthetic Nα-tyrosylated SRIF was labelled with 125I using the lactoperoxidase method and purified on a Sephadex G-10 column. Each organ was homogenized in ice-cold 2N-acetic acid, then suspended in boiling water, centrifuged, and then lyophylized. The sensitivity of the assay varied from 3.9pg to 7.8pg, with the tracer having a specific activity of 100μCi/μg. The displacement curve of extracts from the pancreas and the hypothalamus was shown to be parallel to the standard curve. This antiserum was highly specific for SRIF with negligeble or no cross reactivity. We performed the immunohistochemical study by the enzyme labelled antibody method of Nakane using this anti-SRIF, rabbit anti-glucagon and guinea pig anti-insulin serum.
It was shown using specific RIA that SRIF was contained in the gastrointestinal tract, and especially in the stomach and pancreas. In normal rats, SRIF containing cells were found to be located mainly in the periphery of the pancreatic islets.
The SRIF content of both the pancreas and the isolated islet of streptozotocin-diabetic rats was significantly greater than the content of control rats. SRIF containing cells in islet of the pancreas of diabetic rats were increased in number and scattered into the central portion as well as in the periphery. In the streptozotocin-diabetic rats with daily injections of 1 unit of lente insulin for 4 weeks, the SRIF content of the isolated islet was significantly decreased in comparison with the content of streptozotocin-diabetic rats without insulin.
In C57BL/Ksj dbdb diabetic mice aged from 18 to 28 weeks, the content of SRIF of the pancreas had greatly increased when compared to the content of litter mates. SRIF containing cells in the islet of diabetic mice were increased in number and scattered in the central portion. In C57BL/6J obob diabetic mice, again aged from 18 to 28 weeks, the content of SRIF of the pancreas had only shown a slight increase. In chinese hamsters diabetic due to insulin deficiency, SRIF containing cells were scattered throughout the pancreatic islet.
Because in the diabetic animals described above the pancreatic SRIF had increased, it is conceivable that pancreatic SRIF may be an important factor in the pathogenesis of diabetes mellitus.
