AJP - Cell Physiology, Vol 232, Issue 3 83-C87, Copyright © 1977 by American Physiological Society
Neurotrophic regulation of insulin-sensitive amino acid uptake in rat fast muscle
N. Robbins and P. D. Lyle
Our object was to determine how innervation regulates muscle insulin
sensitivity. Insulin-stimulated uptake of the nonmetabolized amino acid,
2-amino-isobutyric acid, was used as a measure of insulin sensitivity in
denervated rat extensor digitorum longus muscles retaining either a similar
2.5-cm (""proximal denervation'') or a similar to 0.5-cm (""distal
denervation'') length of distal nerve stump. Because both muscles were
inactive in the first 24 h, any difference in insulin sensitivity could be
due only to some trophic influence of the distal nerve stump. Fifteen hours
after either type of denervation, 2-aminoisobutyric acid uptake was
refractory to insulin. However, at 24 h, insulin sensitivity of distally
denervated muscles (with or without a second ipsilateral proximal
denervation) was normal, whereas that of proximally denervated muscles was
still relatively insensitive. In the absence of insulin, the two types of
denervated muscles at 24 h showed no difference in 2-aminoisobutyric acid
uptake. Finally, organ culture of paired muscles with or without long nerve
stumps showed corresponding differences in insulin-stimulated
2-aminoisobutyric acid uptake after 48 h in vitro. Thus, a neurotrophic
factor, independent of impulse activity, stretch, or changes in blood flow,
regulates one type of muscle insulin sensitivity.
