GLUCOSE-HOMEOSTASIS DURING EXERCISE IN HUMANS WITH A LIVER OR KIDNEY-TRANSPLANT

To investigate the role of liver nerve activity on hepatic glucose production 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, respectively. Kidney-transplant (KTX) and healthy control subjects (C) matched 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 in C (2.60 +/- 0.26). At rest plasma renin and insulin were higher and plasma adrenocorticotropic hormone and cortisol lower in transplant corticosteroid-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, respectively. Peripheral glucose uptake was similar to R(a), and glucose remained at basal postabsorptive levels. During exercise the R(a) increase as well as norepinephrine, insulin, and growth hormone responses were similar in LTX compared with both KTX and C. The increase in epinephrine 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 lactate rose more and plasma glycerol and free fatty acid levels were lower in LTX and KTX compared with C. Galactose and indocyanine green clearance 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 activity is important for the renin response to exercise. Finally, mechanisms reducing liver blood flow during exercise are intact after Liver transplantation.