A: The change of plasma glucose in opioid μ-receptor knockout diabetic mice and wild-type controls receiving an oral intake of metformin (100 mg/kg). A: The change of plasma glucose in opioid μ-receptor knockout diabetic mice and wild-type controls receiving an oral intake of metformin (100 mg/kg). B: The plasma BER in same group of mice. Values (means ± SE) were obtained from each group of seven animals. **P < 0.01 vs. data from animals before treatment. Juei-Tang Cheng et al. Diabetes 2006;55:819-825 ©2006 by American Diabetes Association