Training-induced vascular and metabolic adaptations in normo(11 week)- and hyper(18 week)-glycemic obese Zucker rats

The purpose of this study was to investigate the peripheral vascular and metabolic adaptations induced by aerobic training in normoglycemic (11-week-old) and hyperglycemic (18-week-old) insulin-resistant male obese Zucker rats (OZR). OZR were treadmill trained 6-11 (T6-11), 11-18 (T11-18), or 6-18 (T6-18) weeks of age at 15 m/min. 17 percent grade, 1 hour/day, 5 days/week. Forty-eight hours after the last training session and after a 12 hour fast, a tail vein blood sample was obtained for analysis of glucose and insulin concentrations, cholesterol, and glycosylated hemoglobin fraction. Glucose uptake and hindlimb vascular resistance were measured during extracorporeal perfusion of the hindlimb (1.0mU insulin/ml). Trained animals were compared to sedentary age-matched obese (S-OZR) and lean (LZR) animals. S-OZR were hyperinsulinemic and obese at 6 weeks of age, mildly hypercholesterolemic and hyperglycemic at 11 weeks, and profoundly hyperglycemic at 18 weeks. Training did not affect body weight or serum cholesterol. Fasting insulin and glucose concentrations were not different between sedentary and trained OZR, except T6-18 which had higher insulin and lower glucose concentrations. The insulin/glucose ratio was lower in OZR animals and was not altered by 6-7 week training (T6-11, T11-18), but was normalized by 12 week training (T6-18). No significant differences in glycosylated hemoglobin fractions were observed between groups. Normalization of glucose uptake was observed in trained 11-week-old OZR, and a statistically non-significant (P = 0.10) 40 percent improvement was observed in trained 18-week-old OZR. Hindlimb vascular resistance was elevated in the S-OZR, relative to LZR, at 11 and 18 weeks of age, and was reduced with training. One hour/day exercise training normalized hindlimb vascular resistance and glucose uptake in 11-week-old OZR, but only moderately improves these vascular and metabolic variables in 18-week-old hyperglycemic animals. Prolonged (12 weeks) training reduced the severity of fasting hyperglycemia in older animals, but at the expense of an increased fasting insulin concentration.