Beta-endorphin infusion during exercise in rats: blood metabolic effects.

UNLABELLED

Beta-endorphin (betaE) bolus (0.05 mg x kg(-1)) infusion (0.05 mg x kg(-1) x h(-1)) was previously shown in rats to attenuate the decline in plasma glucose during exercise.

PURPOSE

The present investigation compared betaE and saline infusion in rats without a bolus of betaE to determine whether 1) the attenuation in the glucose decline was attributable to the type of administration (bolus betaE + continuous betaE infusion vs continuous betaE infusion), and 2) whether circulating catecholamines or FFAs were in part involved in the glucose decline.

METHODS

Forty untrained Sprague-Dawley rats were randomly assigned to one of four treatments: 1) betaE infusion at rest (betaR), 2) betaE infusion during exercise (betaX), 3) saline infusion at rest (SR), and 4) saline infusion during exercise (SX). Infusions (betaE or saline) with running (22 m x min(-1), 0% grade) lasted 90 min.

RESULTS

A 2 x 2 ANOVA indicated betaE infusion significantly attenuated the decline in plasma glucose due to exercise at 90 min (SX = 4.16 +/- 0.1 vs betaX = 4.61 +/- 0.1 mM). BetaE infusion elevated plasma betaE about 2.5-fold at rest compared with SR and two-fold after exercise (betaX) compared with SX. BetaE infusion had no effect at rest on any of the other variables measured. Exercise significantly increased catecholamines, FFAs and glucagon compared with resting levels. BetaE infusion enhanced the glucagon response to exercise (SX = 577 +/- 67.5 vs betaX = 913 +/- 153 ng x L(-1), P < 0.02). Epinephrine and norepinephrine and FFAs were similar with betaE infusion either at rest or during exercise compared with saline infusion.

CONCLUSION

These results suggest that betaE infusion independent of the betaE bolus can attenuate the decline in glucose during exercise by enhancing glucagon levels and the betaE infusion did not influence circulating catecholamines or FFA's response to exercise.