Early introduction of exercise prevents insulin resistance in postnatal overfed rats

Abstract

Early childhood obesity increases the risk of developing metabolic diseases. We examined the early introduction of exercise in small-litter obese-induced rats (SL) on glucose metabolism in the epididymal adipose tissue (AT) and soleus muscle (SM). On day 3 post-birth, pups were divided into groups of ten or three (SL). On day 22, rats were split into sedentary (S and SLS) and exercise (E and SLE) groups. The rats swam three times/week carrying a load for 30 min. In the first week, they swam without a load; in the 2nd week, they carried a load equivalent to 2% of their body weight; from the 3rd week to the final week, they carried a 5% body load. At 85 days of age, an insulin tolerance test was performed in some rats. At 90 days of age, rats were killed, and blood was harvested for plasma glucose, cholesterol, and triacylglycerol measurements. Mesenteric, epididymal, retroperitoneal, and brown adipose tissues were removed and weighed. SM and AT were incubated in the Krebs-Ringer bicarbonate buffer, 5.5 mM glucose for 1 h with or without 10 mU/mL insulin. Comparison between the groups was performed by 3-way ANOVA followed by the Tukey post-hoc test. Sedentary, overfed rats had greater body mass, more visceral fat, lower lactate production, and insulin resistance. Early introduction of exercise reduced plasma cholesterol and contained the deposition of white adipose tissue and insulin resistance. In conclusion, the early introduction of exercise prevents the effects of obesity on glucose metabolism in adulthood in this rat model.

Figure 1. Insulin tolerance test (1.0 U/kg) at 85 days of age (A) in the sedentary (S), exercise (E), small-litter sedentary (SLS), and small-litter exercise (SLE) groups. B, Glucose disappearance rate (Kitt) of each group. Data are reported as means±SE (n=8-10). *P<0.05; **P<0.005; ***P<0.001 (ANOVA).

Figure 2. Body weight from sedentary (S, n=10), exercise (E, n=11), small-litter sedentary (SLS, n=14), and small-litter exercise (SLE, n=18) rats measured from 22 to 90 days of age (A). Body weight (B) evaluated by area under the curve (AUC). Data are reported as means±SE. ^#P<0.05, SLS vs SLE; *P<0.05, S vs E and SLS (ANOVA).

Figure 3. Food intake (g) in sedentary (S, n=10), exercise (E, n=11), small-litter sedentary (SLS, n=14), and small-litter exercise (SLE, n=18) rats measured from 22 to 90 days of age. Data are reported as means±SE of at least 10 rats per group. P>0.05 (ANOVA).

Figure 4. Weight of mesenteric (A), epididymal (B), retroperitoneal (C), and brown (D) fat tissues from sedentary (S), exercise (E), small-litter sedentary (SLS), and small-litter exercise (SLE) groups. Data are reported as means±SE of 10-18 rats per group. *P<0.05 (ANOVA).

Figure 5. Total lactate (A) and radiochemical lactate (B) production from glucose in isolated incubated soleus muscles obtained from sedentary (S), exercise (E), small-litter sedentary (SLS), and small-litter exercise (SLE) rats. Muscles were incubated in Krebs-Ringer bicarbonate buffer, containing 5.6 mM glucose, 0.1 uCi/mL D-[U¹⁴C] glucose, for 1 h in the absence or presence of 10 mU/mL insulin. Data are reported as means±SE (n=8). *P<0.05 vs non-stimulated (ANOVA).

Figure 6. Total lactate (A) and radiochemical lactate (B) production from glucose by epididymal isolated incubated fat tissues obtained from sedentary (S), exercise (E), small-litter sedentary (SLS), and small-litter exercise (SLE) rats. Epididymal fat tissue was incubated in Krebs-Ringer bicarbonate buffer, containing 5.6 mM glucose, 0.1 uCi/mL D-[U¹⁴C] glucose, for 1 h in the absence or presence of 10 mU/mL insulin. Data are reported as means±SE (n=8). *P<0.05 vs non-stimulated (ANOVA).

Figure 7. [³H]-2-deoxy-D-glucose (2DG) uptake by isolated incubated soleus muscles obtained from sedentary (S), exercise (E), small-litter sedentary (SLS), and small-litter exercise (SLE) rats. Muscles were incubated in Krebs-Ringer bicarbonate buffer, containing 5.6 mM glucose, 0.1 μCi/mL 2-DG, for 1 h in the absence or presence of 10 mU/mL insulin. Data are reported as means±SE (n=8). *P<0.05 (ANOVA).