Fetal Insulin-Like Growth Factor-2 Production Is Impaired in the GK Rat Model of Type 2 Diabetes

P. Serradas, L. Goya, M. Lacorne, M.-N. Gangnerau, S. Ramos, C. Alvarez, A.-M. Pascual-Leone, B. Portha
2002 Diabetes  
At late fetal age (21.5 days postcoitum [dpc]), GK rats present a severely reduced ␤-cell mass compared with Wistar rats. This anomaly largely antedates the onset of hyperglycemia in GK rats. Thus, the ␤-cell mass deficit could represent the primary defect leading to type 2 diabetes in the adult. The aim of this work was to investigate, in GK fetuses at the end of fetal age (21.5 dpc), whether impaired availability of growth factors such as insulin, growth hormone, and IGFs and their IGF
more » ... nd their IGF binding proteins (IGFBPs) could be instrumental in this anomaly. Although it confirms that GK fetuses are hypoinsulinemic despite enhanced plasma glucose level due to maternal hyperglycemia, the present study shows for the first time that IGF-2 expression in the liver and pancreas and IGF-2 serum levels are decreased in GK fetuses. Serum level as well as liver and pancreatic mRNA expression of IGFBP-2 were found to be normal in GK fetuses, whereas serum level and liver mRNA expression of IGFBP-1 were increased. Finally, we found that the maximal ␤-cell mitogenic response to IGFs in vitro is kept intact, therefore suggesting that the direct biological action of IGFs on fetal GK ␤-cells is not grossly impaired. In conclusion, in GK fetuses at 21.5 dpc, the defective IGF-2 production appears to be an early landmark in the pathological sequence leading to retardation of ␤-cell growth in the fetal GK rat. Diabetes 51:392-397, 2002 RESEARCH DESIGN AND METHODS Animals and samples. Pregnant GK and Wistar rats were obtained from our local colony. The morning of the discovery of the vaginal plug was taken as day 0.5 dpc. On day 21.5, dpc pregnant rats were anesthetized with pentobarbital sodium (1 ml/kg body wt i.p.; Sanofi Santé Animale, Sanofi, France). Fetal blood samples were collected at the level of the axillary vessels and centrifuged, and plasma (from one fetus) or serum (from two fetuses) were stored at Ϫ20°C until assayed. Pancreases (from five fetuses) and a piece of liver (from each fetus) were rapidly excised from fetuses, frozen in liquid nitrogen, and then stored at Ϫ70°C until RNA preparation. Determination of plasma glucose, insulin, and GH levels. Plasma glucose was determined with a glucose analyzer (Beckman Instruments, Fullerton, CA). Immunoreactive insulin plasma was estimated as previously described (8). GH was determined in the plasma of fetuses with a rat GH 125 I assay system (Biotrak; Amersham Life Science, Amersham, U.K.). The radioimmunoassay was carried out according to the kit protocol. The sensitivity of the assay was 1.6 ng/ml. Iodination, purification, and determination of serum IGF-1 and -2. Recombinant human IGF-1 and -2 were labeled by a modified chloramine T method (9,10). The specific activity achieved was ϳ90 -175 Ci/g for both peptides. Before IGF-1 and -2 determination, serum IGFBPs were removed by From the
doi:10.2337/diabetes.51.2.392 pmid:11812746 fatcat:qe7o4nyruvcalp2r2vwm4iniuq