Electron microscopy of the pancreatic islets stimulated by insulin antibody

Mice were maintained hyperglycemic by daily intraperitoneal injections of immunoglobulins from guinea pigs highly immunized with beef insulin. Hyperglycemic and control mice were killed throughout a period of 3 weeks. Inflammatory infiltrations around the islets were minimal The stimulated beta cells remained heavily degranulated throughout the period of injections. Insignificant changes were seen on the cytomembrane of the beta cell facing the capillary during the initial period of rapid degranulation and thereafter. The density of the rough endoplasmic reticulum increased progressively. The Golgi complexes expanded and became more elaborate. The mitochondria enlarged. Evidence for the continuous elaboration of secretory granules in the Golgi area and for the existence of an immature pregranule in the formation cycle of the secretory granule was obtained in both normal and hyperglycemic animals. Regressive changes in the cells of the islets were absent. </jats:p

Electron Microscopy of the Pancreatic Islets of the Rat: Effects of Prolonged Insulin Injections

The electron microscopical changes of the pancreatic islets of rats were studied during the phase of transient diabetes and during recovery, following a prolonged period of insulin injections. The most characteristic changes, besides the severe degranulation of the beta cells, were the “inactivity” of the Golgi complex and the absence of special spheroidal bodies from its vicinity. Evidence is presented that these satellite bodies may represent pregranules. Differences in the formation of granules in the Golgi area of the alpha, beta and acinar cell are illustrated and discussed.</jats:p

Biosynthesis of Proinsulin and Other Islet Cell Proteins in Pancreatic Beta Cells of the Rat: A Radioautographic Evaluation of Glucose Effects In Vitro

Rat pancreatic islets were incubated in vitro with L-[4,5-3H]leucine or with L-[2,3-3H]tryptophan in Krebs-Ringer bicarbonate buffer, containing 0, 5, or 20 mM glucose. Incorporation of labeled amino acids in islet cells was evaluated quantitatively by a validated radioautographic procedure. Incorporation of labeled leucine into [3H]proinsulin and [3H]insulin was measured by immunoprecipitation and into other islet proteins by trichloroacetic acid precipitation. Incorporation of labeled amino acids in pancreatic beta cells was patchy and not uniform. Up to 20 to 35% of beta cells, mainly in central regions of the islets, showed poor or no incorporation of label. Peripheral nonbeta, endocrine islet cells and mesenchymal islet cells were all uniformly labeled. Incorporation of either amino acid into nonbeta endocrine and mesenchymal cells was not much affected by the absence of glucose in the incubation buffer. In contrast, incorporation of the amino acids into beta cells was strikingly affected. Incorporation of [3H]leucine into proinsulin and insulin at 0 mM glucose measured by specific immunoprecipitation and by silver grain densities over beta cells was 15 to 20 times less than at 20 mM glucose. Incorporation of [3H]tryptophan, an amino acid absent in proinsulin, into nonhormonal, sedentary beta cell proteins studied by radioautography, similarly, was strikingly affected in the absence of glucose. Thus, radioautography revealed a great sensitivity of both hormonal and nonhormonal protein biosynthesis in the beta cell to the concentration of glucose in the medium.</jats:p

In Vivo Incorporation of [3H] Leucine and [3H] Tryptophan into Proinsulin-insulin and Other Islet Cell Proteins in Normoglycemic, Hyperglycemic, and Hypoglycemic Rats

Rats were infused for brief periods with buffer, glucose, or insulin. L-[4,5-3H] leucine (2.5 mCl) or L-[2,3-3H]-tryptophan (0.5 mCl) was quickly injected intravenously 30 min after the onset of the infusion, when marked hyperglycemia or hypoglycemia had been established. Rats remained connected to the infusion system and were killed 30 min after the injection of the labeled amino acid. Pancreatic islets were isolated by enzymatic digestion of the pancreas. They were processed for radioautography or for the measurement of [3H] proinsulin and [3H] insulin by immunoprecipitation and of other islet [3H]proteins by TCA precipitation. Various tissues of the rats were also removed to measure TCA-precipitable-labeled proteins. Incorporation of [3H]-leucine into proinsulin and insulin was 9 to 10 times greater in the hyperglycemic than in the hypoglycemic rats. Incorporation of [3H]-tryptophan into sedentary beta-cell proteins, measured by the density of silver grain in radioautographs, showed a sixfold difference. The great sensitivity of hormonal and nonhormonal protein biosynthesis of the pancreatic beta cell to plasma glucose was unique among tissues and among other pancreatic islet cells we studied.</jats:p