Evidence for direct action of alloxan to induce insulin resistance at the cellular level

Abstract

To determine whether long-term insulin deficiency alters insulin movement across the endothelium, plasma and lymph dynamics were assessed in dogs after alloxan (50 mg/kg; n = 8) or saline injection (n = 6). Glucose tolerance (KG) and acute insulin response were assessed by glucose injection before and 18 days after treatment. Two days later, hyperglycaemic (16.7 mmol/l) hyperinsulinaemic (60 pmol x min(-1) x kg(-1)) glucose clamps were carried out in a subset of dogs (n = 5 for each group), with simultaneous sampling of arterial blood and hindlimb lymph. Alloxan induced fasting hyperglycaemia (12.9 +/- 2.3 vs 5.7 +/- 0.2 mmol/l; p = 0.018 vs pre-treatment) and variable insulinopenia (62 +/- 14 vs 107 +/- 19 pmol/l; p = 0.079). The acute insulin response, however, was suppressed by alloxan (integrated insulin from 0-10 min: 155 +/- 113 vs 2745 +/- 541 pmol x l(-1) x 10 min(-1); p = 0.0027), resulting in pronounced glucose intolerance (KG: 0.99 +/- 0.19 vs 3.14 +/- 0.38 min(-1); p = 0.0002 vs dogs treated with saline). During clamps, steady state arterial insulin was higher in dogs treated with alloxan (688 +/- 60 vs 502 +/- 38 pmol/l; p = 0.023) due to a 25% reduction in insulin clearance (p = 0.045). Lymph insulin concentrations were also raised (361 +/- 15 vs 266 +/- 27 pmol/l; p = 0.023), such that the lymph to arterial ratio was unchanged by alloxan (0.539 +/- 0.022 vs 0.533 +/- 0.033; p = 0.87). Despite higher lymph insulin, glucose uptake (Rd) was significantly diminished after injection of alloxan (45.4 +/- 2.5 vs 64.3 +/- 6.5 micromol x min(-1) x kg(-1); p = 0.042). This was reflected in resistance of target tissues to the lymph insulin signal (deltaRd/ delta lymph insulin: 3.389 +/- 1.093 vs 11.635 +/- 2.057 x 10(-6) x l x min(-1) x kg(-1) x pmol(-1) x l(-1); p = 0.012) which correlated strongly with the KG (r = 0.86; p = 0.0001). In conclusion, alloxan induces insulinopenic diabetes, with glucose intolerance and insulin resistance at the target tissue level. Alloxan treatment, however, does not alter lymph insulin kinetics, indicating that insulin resistance of Type 1 (insulin-dependent) diabetes mellitus reflects direct impairment at the cellular level.