AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 2 492-R497, Copyright © 1995 by American Physiological Society
Neural control of glucose uptake by skeletal muscle after central administration of NMDA
C. H. Lang, M. Ajmal and A. G. Baillie
Department of Surgery, State University of New York, Stony Brook 11794-8191.
Intracerebroventricular injection of N-methyl-D-aspartate (NMDA) produces
hyperglycemia and increases whole body glucose uptake. The purpose of the
present study was to determine in rats which tissues are responsible for
the elevated rate of glucose disposal. NMDA was injected
intracerebroventricularly, and the glucose metabolic rate (Rg) was
determined for individual tissues 20-60 min later using
2-deoxy-D-[U-14C]glucose. NMDA decreased Rg in skin, ileum, lung, and liver
(30-35%) compared with time-matched control animals. In contrast, Rg in
skeletal muscle and heart was increased 150-160%. This increased Rg was not
due to an elevation in plasma insulin concentrations. In subsequent
studies, the sciatic nerve in one leg was cut 4 h before injection of NMDA.
NMDA increased Rg in the gastrocnemius (149%) and soleus (220%) in the
innervated leg. However, Rg was not increased after NMDA in contralateral
muscles from the denervated limb. Data from a third series of experiments
indicated that the NMDA-induced increase in Rg by innervated muscle and its
abolition in the denervated muscle were not due to changes in muscle blood
flow. The results of the present study indicate that 1) central
administration of NMDA increases whole body glucose uptake by
preferentially stimulating glucose uptake by skeletal muscle, and 2) the
enhanced glucose uptake by muscle is neurally mediated and independent of
changes in either the plasma insulin concentration or regional blood flow.
