Young, lean MIP-CCK mice have normal glucose homeostasis and β-cell mass. IP-GTT was performed on male mice aged 12 wk. A and B: glucose (P = 0.95) and insulin (P = 0.94) values were similar at all time points (n = 4). There were also no differences in fasting glucose or insulin values (time 0 min). IPTT was performed on male mice aged 12 wk. C: insulin sensitivity was not different from wild type (n = 4, P = 0.93). D: there was no difference in glucose-stimulated insulin secretory capacity at low (P = 0.81) or high (P = 0.23) glucose in isolated islets from 8-wk-old animals. Filled bars, low glucose (1.7 mM); open bars, high glucose (16.7 mM) (n = 4). E: total pancreatic insulin content did not differ from wild type in 8-wk-old animals (n = 7–8, P = 0.64). F and G: quantitative analysis from pancreatic sections demonstrated normal β-cell mass (P = 0.83) and fractional islet area (P = 0.28) in MIP-CCK mice (n = 4). H: no change in percent Ki67-positive β-cells was observed (n = 4, P = 0.87).