EFFECT OF LIVER DENERVATION ON GLUCOSE-PRODUCTION DURING RUNNING IN GUINEA-PIGS

Activity in sympathetic liver nerves has been proposed to be important for glucose production in exercising humans. However, liver denervati on does not influence the exercise-induced increase in glucose product ion in the rat and dog. These species have a poor sympathetic liver in nervation in contrast to the rich innervation in humans. The effect of liver denervation on glucose production during exercise was therefore studied in the guinea pig, a species with a rich sympathetic hepatic innervation comparable to that of humans. Guinea pigs were selectively liver denervated (n = 9) or sham operated (n = 8) and instrumented wi th a carotid and a jugular catheter. One week later they ran on a trea dmill at 32 m/min for 20 min. Glucose turnover was evaluated by a prim ed constant-rate intravenous infusion of [3-H-3]glucose. Arterial bloo d was sampled for analysis of hormones and metabolites. At rest, liver -denervated guinea pigs had lower glucose turnover and plasma concentr ations of glucose, glycerol, and cortisol than control animals. During running, the increase in hepatic glucose production was similar in th e two groups (4.1 +/- 0.8 vs. 3.8 +/- 0.7 mu mol.min(-1).100 g(-1) in control animals) and so were hepatic (247 +/- 25 vs. 246 +/- 45 mmol g lucose units/kg wet wt in control animals) and muscle glycogen concent rations at the end of exercise. Exercise-induced increases were also s imilar in the two groups for epinephrine (1.9 +/- 0.3 vs. 1.6 +/- 0.2 nM in control animals), norepinephrine (13.0 +/- 1.9 vs. 11.1 +/- 2.3 nM in control animals), cortisol [0.41 +/- 0.03 vs. 0.57 +/- 0.08 mu M in control animals (P = 0.09)], and glycerol [47 +/- 7 vs. 70 +/- 12 mu M in control animals (P = 0.103)]. In conclusion, sympathetic liver nerve activity is not a prerequisite for the exercise-induced increas e in glucose production in the guinea pig.