Diabetic GK rat plasma but not normal Wistar rat plasma induces insulin-stimulated DNA synthesis in primary cultured smooth muscle cells in GK rat aorta.

We investigated the effect of diabetic plasma on insulin-stimulated DNA synthesis in primary cultured aortic smooth muscle cells (SMC) of the GK rat, a model of non-insulin-dependent diabetes mellitus, and compared it with that of Wistar normal rat plasma. We measured the incorporation of 3H-thymidine into cultured SMC. The diabetic plasma (3%) of GK rat, but neither the plasma (3%) of Wistar normal rat nor the plasma (3%) (not containing both insulin-like growth factor-I (IGF-I) and corticosterone) of Wistar hypophysectomized rat induced insulin-stimulated DNA synthesis in GK rat SMC. The responsiveness of SMC to insulin, not to IGF-I, was decreased remarkably by the diabetic state. The diabetic plasma of GK rat remarkably enhanced and the plasma of Wistar hypophysectomized rat weakly enhanced insulin-stimulated DNA synthesis in Wistar normal rat SMC. Corticosterone (20 nM) increased insulin-stimulated DNA synthesis in GK rat SMC but decreased it in Wistar normal rat SMC, using the plasma of Wistar hypophysectomized rat. Corticosterone levels were lower in GK rat plasma than in normal Wistar rat plasma. These results demonstrate that the enhancement of insulin-stimulated DNA synthesis in diabetic SMC by the diabetic plasma of GK rat may be due to neither IGF-I nor corticosterone but due to other factors.