Training improves glucose homeostasis in rats during exercise via glucose production

Donovan, C.M.; Sumida, K.D.

American Journal of Physiology 258(3 Pt 2): R770-R776


ISSN/ISBN: 0002-9513
PMID: 2316721
Document Number: 366397
The effects of endurance training (running 1 h/day at 35 m/min, 10% grade) on glucose homeostasis during exercise (running 20 m/min) was studied in 30-h fasted rats. Primed-continuous infusions of [6-3H]- and [U-14C]glucose were employed to assess rates of appearance (Ra), disappearance (Rd), and apparent recycling. Training resulted in a 65% increase in skeletal muscle succinate dehydrogenase (SDH) activity but did not significantly influence body weight. Resting blood glucose concentrations were not significantly different between controls, 5.01 .+-. 0.19 mM, and trained animals, 4.86 .+-. 0.16 mM. Exercise resulted in a more rapid decline in blood glucose levels for control animals, reaching a value of 2.35 .+-. 0.39 mM at 60 min, compared with 3.69 .+-. 0.47 mM for trained animals. Glucose Ra was not significantly different between groups at rest, and rose for both groups during exercise. However, for controls Ra plateaued between 15 and 60 min of exercise at 11.03 .+-. 0.73 .mu.mol .cntdot. 100 g-1 .cntdot. min-1, whereas trained animals demonstrated a continuous rise to 17.13 .+-. 1.18 .mu.mol .cntdot. 100 g-1 .cntdot. min-1. Glucose Rd values were not significantly different between groups during the first 30 min of exercise but were significantly higher for trained animals during the final 30 min. As a result of the higher glucose Ra, trained animals demonstrated a smaller mean difference between Ra and Rd during exercise when compared with controls, -0.27 .+-. 0.14 vs. -0.96 .+-. 0.17 .mu.mol .cntdot. 100 g-1 .cntdot. min-1. Trained animals further demonstrated significantly higher rates of glucose carbon recycling during the final 30 min of exercise. The liver glycogen content was essentially depleted by the 30-h fast and the amount mobilized during exercise could only account for .apprx. 6 min of the initial Ra. The elevated glucose production after training appears attributable to elevated rates of gluconeogenesis.

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