Decreased Insulin Secretion by Isolated Pancreatic Islets from Rats Fed 4% Protein Diet

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Abstract
Male weanling rats were fed either 4 or 16% (control) protein diets for 10-12 wk. The animals were administered an i.v. injection of 30% glucose solution (3 g/kg body wt) and glucose tolerance was determined. The glucose tolerance in rats fed low protein diets was not significantly different from that of the control rats, indicating that clearance of high blood glucose levels in the animals fed low protein diets was not affected. Using a collagenase digestion technique, islets of Langerhans were isolated from another set of animals fed 4% or control diets. When these islets were perifused with a medium containing glucose, there was a typical biphasic insulin [I] secretory response. The isolated islets from low protein fed rats exhibited considerably low I secretory response when exposed to medium containing 16.7 mM glucose (300 mg/dl), although no difference was found in the pancreatic I content of normal and low protein fed rats. This indicates that decreased I secretion could not be due to a decreased available pool of I. When glucagon (5 .mu.g/ml medium) or arginine (20 mM) was added to a medium containing 8.4 mM glucose (150 mg/dl), the in vitro I release by the islets obtained from protein malnourished and control rats was enhanced. Again the control rat islets secreted much greater amounts of I. I secreted by the islets in response to glucagon (5 .mu.g/ml medium) was greater than that secreted in response to 16.7 mM glucose. The decreased I secretory response of islets from protein malnourished animals may be due to a diminished number of glucose recognition sites on the .beta.-cells.