M. Kjaer et al., REGULATION OF HEPATIC GLUCOSE-PRODUCTION DURING EXERCISE IN HUMANS - ROLE OF SYMPATHOADRENERGIC ACTIVITY, The American journal of physiology, 265(2), 1993, pp. 50000275-50000283
To investigate the role of sympathoadrenergic activity on glucose prod
uction (R(a)) during exercise, eight healthy males bicycled 20 min at
41 +/- 2 and 74 +/- 4% maximal O2 uptake (VO2max; mean +/- SE) either
without (control; Co) or with blockade of sympathetic nerve activity t
o liver and adrenal medulla by local anesthesia of the celiac ganglion
(BI). Epinephrine (Epi) was in some experiments infused during blocka
de to match (normal Epi) or exceed (high Epi) Epi levels during Co. A
constant infusion of somatostatin and glucagon was given before and du
ring exercise. At rest, insulin was infused at a rate maintaining eugl
ycemia. During intense exercise, insulin infusion was halved to mimic
physiological conditions. During exercise, R(a) increased in Co from 1
4.4 +/- 1.0 to 27.8 +/- 3.0 mumol . min-1 . kg-1 (41% VO2max) and to 4
2.3 +/- 5.2 (74% VO2max; P < 0.05). At 41% VO2max, plasma glucose decr
eased, whereas it increased during 74% VO2max. R(a) was not influenced
by Bl. In high Epi, R(a) rose more markedly compared with control (P
< 0.05), and plasma glucose did not fall during mild exercise and incr
eased more during intense exercise (P < 0.05). Free fatty acid and gly
cerol concentrations were always lower during exercise with than witho
ut celiac blockade. We conclude that high physiological concentrations
of Epi can enhance R(a) in exercising humans, but normally Epi is not
a major stimulus. The study suggests that neither sympathetic liver n
erve activity is a major stimulus for R(a) during exercise. The R. res
ponse is enhanced by a decrease in insulin and probably by unknown sti
muli. Finally, splanchnic fat stores may be mobilized by sympathetic n
erve activity during exercise.