[Study on the insulin and insulin receptor in the progression of renal ischemic and reperfusion]

To evaluate the effect of insulin and it's receptor on the kidney of rabbit with acute ischemic/reperfusion injury.

Twenty three Japanese white rabbits were allocated randomly into the control group, ischemic/reperfusion group(IR group), and insulin treatment group(Ins-IR group). The IR group received clamping for 1 h followed by 2 h or 48 h of reperfusion. In the Ins-IR group, insulin injection (Ins 3U/kg, glucose 1.5 g/kg, K+ 4 mg/kg, Mg2+ 1.7 mg/kg) was administered intravenously twice a day for two days, whereas only normal saline in equal amount was given to the IR group and control group. At 2 h or 48 h after reperfusion, glucose and insulin in serum were determined. Rough plasma of renal tissue was prepared by repeated centrifugation. Insulin receptor in renal tissue was analyzed by radiologand binding assay. The binding data were calculated according to Scatchard using the ligand program. Statistical significance was analyzed with the paired t-test.

The level of blood glucose increased after 2 h reperfusion in three groups, but the level in IR group increased much higher than those in control and Ins-IR groups(P < 0.05). The level of serum insulin of IR group after 2 h reperfusion was significantly higher than that of control (P < 0.05). Scatchard analysis showed curvilinear profiles, indicating that there are two classes of receptors with different affinity or the presence of a single class of receptors with a negative cooperative hormone-receptor interaction. Data analyzed by a two-site model showed that the values of Bmax1 (high affinity site), Bmax2 (low affinity site) and Kd1, Kd2 after 2 h reperfusion were significantly lower than those of control (P < 0.05). In IR-Ins group, only Bmax2 decreased (P < 0.05, compared with control). 48 h after IR there was no difference in Bmax1, Kd1 between the 3 groups, but Bmax2 of IR-Ins group was still lower than that of control (P < 0.001) and IR group (P < 0.05). The Kd2 of IR group increased (P < 0.05 compared with control and IR-Ins group).

The results indicate that the effect of intrinsic insulin decreases during renal ischemic/reperfusion. The extrinsic insulin can protect renal tissue through its high affinity receptor. There exits down-regulation of low affinity receptor but none of high affinity receptor during insulin treatment.