INFLUENCE OF PERI-ARTERIAL HEPATIC DENERVATION ON THE GLYCEMIC RESPONSE TO EXERCISE IN RATS

Exercise is known to increase hepatic glucose production. Previous stu dies have suggested that the sympathetic nerves only marginally contri bute to this process. This study examined whether increased catecholam ine response or increased adrenoceptor sensitivity might have affected previous results showing no effect of hepatic denervation on the incr eased hepatic glucose production during exercise. Hepatic sympathetic denervated rats, sham-operated rats and control rats were forced to sw im against a counter current for 15 minutes. Denervations and sham ope rations were performed 9 days prior to swimming. The results show that denervation did not affect the changes in levels of blood glucose, pl asma FFA, and catecholamines before, during and after swimming. Furthe rmore, hepatic adrenoceptor sensitivity was not altered in denervated rats, since intravenous infusions of epinephrine (20 ng/min) and norep inephrine (50 ng/min) similarly changed blood glucose and plasma FFA l evels in liver-denervated, sham-operated and control rats. Thus, the i ncrease in blood glucose levels during intravenous infusion of epineph rine and norepinephrine in the respective groups was 1.2 +/- 0.3 and 1 .0 +/- 0.3 mmol/l (liver-denervated rats), 1.6 +/- 0.4 and 0.7 +/- 0.3 mmol/l (sham-operated rats) and 1.3 +/- 0.3 and 0.8 +/- 0.3 mmol/l (c ontrol rats), respectively. After adrenodemedullation, however, the ri se of glucose levels during swimming in liver-denervated and control r ats was completely abolished. Thus, the glucose response to swimming w ith and without adrenodemullation was 0.1 +/- 0.4 and 1.7 +/- 0.4 mmol /l in liver-denervated rats (P < 0.01) and -0.2 +/- 0.4 and 2.2 +/- 0. 2 mmol/l in control rats (P < 0.001), respectively. The study therefor e suggests that the peri-arterial hepatic nerves have a negligible inf luence on the glycemic response to exercise in rats. Instead, the glyc emic response seems to be mediated mainly by the adrenal medulla.