Regulation of net hepatic substrate balance by phenacylimidazolium ions in the conscious dog.

Phenacylimidazolium ions have the capacity to promote hepatic glycogen synthesis in vitro via activation of glycogen synthase and inactivation of phosphorylase. The purpose of the present study was to determine whether these compounds alter net hepatic substrate balance in vivo. Following a control period somatostatin was infused into 42h-fasted, conscious dogs and insulin (3X-basal) and glucagon (basal) were replaced intraportally. The glucose load to the liver was doubled with a peripheral glucose infusion and the phenacylimidazolium compound, 254236 (EX; n = 5) was infused intraportally at varying rates in four separate periods (0 (P1), 0.5 (P2), 1.0 (P3), 2.0 (P4) mumol kg-1 min-1). In a separate group of animals (C; n = 5) saline was infused intraportally during P1-P4 to match the volume rate of delivery that occurred in EX. In C net hepatic glucose uptake was 8.5 +/- 1.7 mumol kg-1 min-1 during P1 and did not change significantly throughout the study. In EX net hepatic glucose uptake increased (p < 0.05) from 9.0 +/- 2.5 during P1 to 16.2 +/- 3.1 mumol kg-1 min-1 during P4. Whereas net hepatic lactate output was evident throughout P1-P4 in C, the liver consistently switched to net lactate uptake during P3 (1.2 +/- 1.7 mumol kg-1 min-1) and P4 (2.2 +/- 1.0 mumol kg-1 min-1) in EX. Sympathoadrenal activation (increased catecholamines) was evident in EX during period 4. The increased hepatic retention of carbon (glucose and lactate) coincident with 254236 infusion in conscious dogs is less than that observed in vitro but is consistent with a role for phenacylimidazolium ions in promoting hepatic glycogen synthesis.