FNDC5 and hyperinsulinism: Likewise, as shown in Figure 4D, hyperinsulinemia was also exhibited in homozygous db/db animals as compared to heterozygous mice (serum insulin: 0.81 ± 0.065 ng/ml in heterozygous control vs. 8.33 ± 0.69 ng/ml in homozygous db/db control, p<0.0001), but irisin treatment also resulted in a marked decrease in serum insulin (serum insulin 8.32 ± 0.68 ng/ml in homozygous db/db control vs 6.56 ± 0.38 ng/ml in homozygous db/db irisin treatment, p<0.01 vs homozygous db/db control).