The effect of putative insulin-like substances released by the motor nerve on glucose transport in perfused rat muscle.
Motor nerves have been claimed to contain and release immunoreactive insulin. We studied whether release of insulin or other non-acetylcholine substances is important for (1) the increase in glucose transport normally seen during motor nerve activated contraction, and (2) the increase in insulin sensitivity induced by contractions. Ad 1:Rat hindquarters were perfused and one sciatic nerve was stimulated during motor nerve end plate blockade (Pancuronium bromide, 33 micrograms ml-1). Muscle glucose transport (3-O-[14C]-methylglucose (3-O-MG) uptake, 3 mM) was identical (P > 0.05) in stimulated compared with nonstimulated white gastrocnemius, red gastrocnemius and soleus muscle. This was also true when, prior to end plate blockade, muscles had been stimulated to contract to increase insulin sensitivity. No immunoreactive insulin was found in venous perfusate. Ad 2: Rats had both sciatic nerves cut. One week later hindquarters were perfused and calf muscles of one leg were directly stimulated to contract. Subsequently, 3-O-MG uptake in muscle was determined with and without submaximal insulin (100 microU ml-1). In contrast to previous findings in innervated muscle, responses to insulin were identical (P > 0.05) with and without prior contractions.


CONCLUSIONS
The increase in muscle glucose transport normally seen in response to motor nerve stimulation is related to the contraction process and not even partly mediated by release of insulin-like substances from the nerve. In contrast, release of a non-acetylcholine substance from the motor nerve may be involved in the exercise induced increase in insulin sensitivity.
Han
X
X
Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark.
Galbo
H
H
D000818:Animals; D001692:Biological Transport; D003714:Denervation; D004558:Electric Stimulation; D005947:Glucose / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D007328:Insulin / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D009045:Motor Endplate / Q000187:drug effects / Q000378:metabolism*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000294:innervation / Q000378:metabolism* / Q000502:physiology; D010197:Pancuronium / Q000494:pharmacology; D010477:Perfusion; D051381:Rats; D017208:Rats, Wistar
D007328:Insulin; D006003:Glycogen; D005947:Glucose; D010197:Pancuronium