beta-endorphin infusion during exercise in rats: blood metabolic effects

beta-endorphin (beta E) bolus (8.05 mg.kg(-1)) infusion (0.05 mg.kg(-1).h(- 1)) was previously shown in rats to attenuate the decline in plasma glucose during exercise, Purpose: The present investigation compared beta E and sa line infusion in rats without a bolus of beta E to determine whether 1) the attenuation in the glucose decline was attributable to the type of adminis tration (bolus beta E + continuous beta E infusion vs continuous beta E inf usion), and 2) whether circulating catecholamines or FFAs were in part invo lved in the glucose decline. Methods: Forty untrained Sprague-Dawley rats w ere randomly assigned to one of four treatments: 1) beta E infusion at rest (beta R), 2) beta E infusion during exercise (beta X), 3) saline infusion at rest (SR), and 4) saline infusion during exercise (SX). Infusions (beta E or saline) with running (22 m.min(-1), 0% grade) lasted 90 min. Results: A 2 X 2 ANOVA indicated beta E infusion significantly attenuated the declin e in plasma glucose due to exercise at 90 min (SX = 4.16 +/- 0.1 vs beta X = 4.61 +/- 0.1 mM). beta E infusion elevated plasma beta E about 2.5-fold a t rest compared with SR and two-fold after exercise beta X) compared with S X. beta E infusion had no effect at rest on any of the other variables meas ured. Exercise significantly increased catecholamines, FFAs and glucagon co mpared with resting levels. PE infusion enhanced the glucagon response to e xercise (SX = 577 +/- 67.5 vs PX = 913 + 153 ng.L-1, P < 0.02). Epinephrine and norepinephrine and FFAs were similar with beta E infusion either at re st or during exercise compared with saline infusion. Conclusion: These resu lts suggest that beta E infusion independent of the beta E bolus can attenu ate the decline in glucose during exercise by enhancing glucagon levels and the SE infusion did not influence circulating catecholamines or FFA's resp onse to exercise.