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

Summary 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 (K_G) 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 · min⁻¹· 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 · l⁻¹· 10 min⁻¹; p = 0.0027), resulting in pronounced glucose intolerance (K_G: 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 (R_d) was significantly diminished after injection of alloxan (45.4 ± 2.5 vs 64.3 ± 6.5 μmol · min⁻¹· kg⁻¹; p = 0.042). This was reflected in resistance of target tissues to the lymph insulin signal (ΔR_d/Δlymph insulin: 3.389 ± 1.093 vs 11.635 ± 2.057 · 10⁻⁶· l · min⁻¹· kg^–1· pmol⁻¹· l⁻¹; p = 0.012) which correlated strongly with the K_G (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. Diabetologia (1998) 41: 1327–1336] Received: 3 November 1997 and in final revised form: 2 June 1998