Protein turnover was normalized in insulin-treated women with GDM; however, fasting and postprandial plasma concentrations of amino acids were elevated in the antepartum and postpartum periods, despite satisfactory maternal glycemic control.

RNA preparations from isolated rat pancreatic islets and from human insulinomas were injected into oocytes of Xenopus laevis which were then incubated with[3H]leucine. Acid-ethanol extracts of the oocytes were immunoprecipitated with anti-insulin serum using the double antibody technique. Sodium dodecyl sulfate disc gel electrophoresis of the immunoprecipitates showed the presence of an insulin-displaceable immunoreactive material with a molecular weight of about 18,000 in extracts from oocytes injected with RNA of 9-11 S. This immunoreactive product was not detected in extracts from oocytes injected with buffer or 4-8S RNA or RNA heavier than 11 S. These observations suggest the involvement of a precursor larger than proinsulin in the biosynthesis of insulin.It is now well established that the biosynthesis of insulin in the pancreatic beta cell proceeds via a single-chain polypeptide precursor which has been identified and characterized as proinsulin (1-5). Based on a molecular weight for proinsulin of approximately 10,000, it can be speculated that the translation of the messenger RNA for proinsulin would require the participation of three ribosomes. Studies by Permutt and Kipnis (6) on the stimulatory effect of glucose on protein synthesis in isolated rat pancreatic islets provided indirect support for this speculation. Tjioe and Kroon (7) immunoassayed for insulin in polysome preparation from rat islets and concluded that trisomes participated in the biosynthesis of insulin. However, we (8) have observed that immunoassayable insulin was mainly associated with tetrasomes and pentasomes obtained from fetal bovine pancreas, when the breakdown of polysomes by RNase was completely prevented by antibody against RNase. Our observation suggests that polysomes larger than trisomes may be involved in the biosynthesis of insulin. The participation of polysomes larger than expected could be due to either the presence of untranslatable regions of nucleotides in the messenger RNA or the synthesis of a protein larger than anticipated. In order to establish if a protein larger than proinsulin is synthesized, we have extracted and fractionated RNA from isolated rat pancreatic islets and from human insulinomas and have used the RNA fractions as templates for protein synthesis in the oocytes of Xenopus laevis.MATERIALS AND METHODS Preparation of RNA. RNA was extracted from the tissue homogenate using phenol according to the method of Palmiter (9). Five thousand rat islets isolated by the collagenase method of Lacy and Kostianovsky (10) and two human insulinomas were extracted. The RNA preparation was fractionated by centrifugation through a 10-20% sucrose gradient in 0.01 M tris(hydroxymethyl)aminomethane (Tris)-HCI, pH (500 ,Ci/ml) for 40 hr followed by three successive changes of medium containing nonradioactive leucine (1 mg/ml) at 30 min intervals. The oocytes were then homogenized in 0.5 ml of acid-ethanol (75 ml of absolute ethanol, 1.5 ml of concentrated HC1, and water to 100 ml). The homogenate was centrifuged ...

No abstract

Pancreatic islet-cell function and volume are both key determinants of the maintenance of metabolic health. Insulin resistance and islet-cell dysfunction often occur in the earlier stages of type 2 diabetes (T2D) progression. The ability of the islet cells to respond to insulin resistance by increasing hormone output accompanied by increased islet-cell volume is key to maintaining blood glucose control and preventing further disease progression. Eventual β-cell loss is the main driver of full-blown T2D and insulin-dependency. Researchers are targeting T2D with approaches that include those aimed at enhancing the function of the patient’s existing β-cell population, or replacing islet β-cells. Another approach is to look for agents that enhance the natural capacity of the β-cell population to expand. Here we aimed to study the effects of a new putative β-cell growth factor on a mouse model of pre-diabetes. We asked whether: 1) 4-week’s treatment with vesiculin, a two-chain peptide derived by processing from IGF-II, had any measurable effect on pre-diabetic mice vs vehicle; and 2) whether the effects were the same in non-diabetic littermate controls. Although treatment with vesiculin did not alter blood glucose levels over this time period, there was a doubling of the Proliferating Cell Nuclear Antigen (PCNA) detectable in the islets of treated pre-diabetic but not control mice and this was accompanied by increased insulin- and glucagon-positive stained areas in the pancreatic islets.