INSR and type 2 diabetes mellitus: Furthermore, the early rapid and then sustained decrease in the ICR after glucose ingestion was likely caused by the rapid and progressive increase in the ISR that then slowed (in the Ob-NFG-IGT, Ob-IFG-IGT and Ob-T2D groups) or decreased (in the lean and Ob-NFG-NGT groups), in conjunction with a reduced availability of cell surface insulin receptors.