M. Kjaer et al., GLUCOSE-HOMEOSTASIS DURING EXERCISE IN HUMANS WITH A LIVER OR KIDNEY-TRANSPLANT, American journal of physiology: endocrinology and metabolism, 31(4), 1995, pp. 636-644
To investigate the role of liver nerve activity on hepatic glucose pro
duction during exercise, Liver-transplant subjects (LTX, n = 7, 25-62
yr, 4-18 mo postoperative) cycled for 40 min, 20 min at 52 +/- 3% (SE)
maximal O-2 consumption (VO2max) and 20 min at 83 +/- 1% VO2max, resp
ectively. Kidney-transplant (KTX) and healthy control subjects (C) mat
ched for sex and age exercised at the same %VO2max as LTX. VO2max was
lower in both LTX (1.59 +/- 0.12 l/min) and KTX (1.59 +/- 0.07) than i
n C (2.60 +/- 0.26). At rest plasma renin and insulin were higher and
plasma adrenocorticotropic hormone and cortisol lower in transplant co
rticosteroid-treated subjects compared with C. In LTX, hepatic glucose
production (R(a)) increased from 11.9 +/- 0.9 (rest) to 17.6 +/- 1.8
and 25.5 +/- 1.8 mu mol . min(-1). kg(-1) at 52 and 82% VO2max, respec
tively. Peripheral glucose uptake was similar to R(a), and glucose rem
ained at basal postabsorptive levels. During exercise the R(a) increas
e as well as norepinephrine, insulin, and growth hormone responses wer
e similar in LTX compared with both KTX and C. The increase in epineph
rine was smaller in LTX than in C, the only group showing an increase
in cortisol. The increase in plasma renin activity during exercise was
attenuated in KTX compared with LTX and C. During exercise blood lact
ate rose more and plasma glycerol and free fatty acid levels were lowe
r in LTX and KTX compared with C. Galactose and indocyanine green clea
rance were similar in all groups at rest and decreased with increasing
work load similarly in LTX, KTX, and C. In conclusion, during dynamic
exercise glucose homeostasis is well maintained in LTX. Accordingly,
liver nerve activity is not important for the exercise-induced rise in
hepatic glucose production in humans. In contrast, kidney nerve activ
ity is important for the renin response to exercise. Finally, mechanis
ms reducing liver blood flow during exercise are intact after Liver tr
ansplantation.