Serum proteins. (A, B, C, D and E) Circulating levels of IGFBP1, IGFBP2, IGFBP3, IGFBP5 and IGFBP6 in serum from 16-week-old mice were measured using a Milliplex magnetic bead panel. (F) Circulating levels of total (free and bound) IGF-I in serum from 16-week-old mice were measured by ELISA. (n = 9/genotype/gender, *t-test P value <0.05.)