Figure 6.

Muscle Igf1 deletion alters body composition and glucose handling in an age-dependent manner. Body composition analysis by time-domain–NMR in 8 wk (n = 4) (A), 12 wk (n = 6) (E), and 16 wk (n = 6) (I) male bMID mice revealed a progressive increase in their fat levels with age without a significant alteration in their lean mass percentage until 16 wk of age. No changes in either the fat or lean mass percentage was observed in control mice, at the time points examined. Blood glucose levels were measured in mice aged 8 wk (n = 7–8) (B), 12 wk (n = 4) (F), and 16 wk (n = 6–7) (J) bMID mice and their age-matched controls when unfed overnight or randomly fed. Control but not bMID mice responded to food deprivation, with reduced glucose levels. Intraperitoneal GTTs showed no significant differences in 8 wk (n = 7–8) (C) and 12 wk (G) (n = 4–5) bMID mice, and delayed glucose clearance in 16-wk-old bMID mice (K) vs. age-matched control mice (n = 5–8). Serum insulin was elevated in 8-wk-old bMID (D), did not change in 12-wk-old bMID (H), and was reduced in 16-wk-old bMID (L) mice compared with their age-matched controls) (n = 4–5). Data are represented as means ± sem. Analysis by 1-way ANOVA, followed by Sidak’s multiple comparisons test. Insulin level comparisons were analyzed by a Student’s t test. *P < 0.05, **P < 0.01, ***P < 0.001 (bMID vs. control), ^†P < 0.05 (fed vs. unfed) by Student’s t test.