Journal of Applied Physiology, Vol 65, Issue 2 744-749, Copyright © 1988 by American Physiological Society
Stimulatory role for endogenous opioid peptides on postexercise insulin secretion in rats
P. A. Farrell, B. Sonne, K. Mikines and H. Galbo
Department of Medical Physiology-B, Panum Institute, University of Copenhagen, Denmark.
Endogenous opioid peptides (EOP) and prior exercise may modulate the
stimulatory effect of glucose on insulin secretion. To gain insights into
these relationships, we studied male Wistar rats (187-245 g) during
sustained hyperglycemia by use of the glucose clamp technique. Four groups
of sedentary fed rats (n = 8/group) either ran (Ex) at 24 m/min, 0% grade,
or rested (R) for 40 min. Thirty minutes after Ex or R, arterial blood
glucose was elevated to and maintained at 11 mM for 2 h by a variable
glucose infusion. At the start of Ex or R rats had saline (Sal) or naloxone
(Nal, an opioid antagonist) intravenous infusions for 160 min (40 min Ex +
30 min R + 90 min of a 120-min glucose clamp). Steady-state glucose
infusion rates (SSGIR) were approximately 55 mg.kg-1.min-1 at the start of
the clamp and declined significantly over the 2nd h to approximately 45
mg.kg-1.min-1. No significant differences existed in SSGIR between groups.
R-Sal and Ex-Sal groups did not differ in their insulin response to
hyperglycemia. In contrast, when all groups were compared at the end of the
Nal or Sal infusion, Ex-Nal had the lowest insulin concentration (749 +/-
174 pmol/l), whereas the R-Nal group had the highest (1,581 +/- 216 pmol/l,
P less than 0.05). These data suggest a stimulatory role for EOP on insulin
secretion that is expressed after a prior stress (Ex). Thus one function of
exercise-induced activation of EOP may be to regulate insulin secretion in
the immediate postexercise period.
