Affiliations: [a] Department of Physiology, Faculty of Medicine, Gazi
University, Ankara, Turkey | [b] Department of Physiology, Faculty of Medicine,
Başkent University, Ankara, Turkey | [c] Department of Physiology, Department of Physiology,
Dokuz Eylul University, İzmir, Turkey
Note: [] Corresponding author: Şevin Güney, PhD, Department
of Physiology, Faculty of Medicine, Gazi University, 06510 Beşevler
Ankara Turkey. Tel.: +90 3122024716; Fax: +90 3122124647; E-mail:
sguney@gazi.edu.tr
Abstract: Physical exercise increases the level of endogenous opiates that
possibly play a major role for integration of hormonal and metabolic responses
to exercise. Increased endogenous opioids in response to physical activity may
enhance the performance through decreasing pain perception. However, what
possible effect the opioid peptides have on physical exercise at the level of
central nervous system remains to be elucidated. In this study, naloxone (N=6),
and naltrindole (N=8) were administered intracerebroventrically to rats. A
physiologic saline group (N=10) and a control group (N=8) were also included in
the study. All groups were then subjected to exhaustive exercise on a
treadmill. Besides recording the exhaustion time, blood glucose and lactate
levels were measured before and after exercise. Treatments with naloxone and
naltrindole had no effect on the exhaustion time. In comparison with
pre-exercise period, lactate levels increased, while glucose levels decreased
significantly in the blood of all animals during post-exercise period. However,
decreased level of glucose in the post-exercise period was statistically
significant only in those treated with naltrindole, compared with the other
groups. Our findings indicate that the central endogenous opioid peptides may
have a role in the regulation of glucose metabolism during exhaustive exercise.
This effect can be mediated via delta opioid receptors, although they exert no
effect on the performance, namely, on the exhaustion time.
