Chronic hepatic artery ligation does not prevent liver from differentiating portal vs. peripheral glucose delivery

Abstract

Infusion of glucose into the hepatic artery blocks the stimulatory effect of the “portal signal” on net hepatic glucose uptake (NHGU) during portal glucose delivery. We hypothesized that hepatic artery ligation (HAL) would result in enhanced NHGU during peripheral glucose infusion because the arterial glucose concentration would be perceived as lower than that in the portal vein. Fourteen dogs underwent HAL ∼16 days before study. Conscious 42-h-fasted dogs received somatostatin, intraportal insulin, and glucagon infusions at fourfold basal and at basal rates, respectively, and peripheral glucose infusion to create hyperglycemia. After 90 min ( period 1), seven dogs (HALpo) received intraportal glucose (3.8 mg · kg–1 · min–1) and seven (HALpe) continued to receive only peripheral glucose for 90 min ( period 2). These two groups were compared with nine non-HAL control dogs (control) treated as were HALpe. During period 2, the arterial plasma insulin concentrations (24 ± 3, 20 ± 1, and 24 ± 2 μU/ml) and hepatic glucose loads (39.1 ± 2.5, 43.8 ± 2.9, and 37.7 ± 3.7 mg · kg–1 · min–1) were not different in HALpe, HALpo, and control, respectively. HALpo exhibited greater ( P < 0.05) NHGU than HALpe and control (3.1 ± 0.3, 2.0 ± 0.4, and 2.0 ± 0.1 mg · kg–1 · min–1, respectively). Net hepatic carbon retention was approximately twofold greater ( P < 0.05) in HALpo than in HALpe and control. NHGU and net hepatic glycogen synthesis during peripheral glucose infusion were not enhanced by HAL. Even though there exists an intrahepatic arterial reference site for the portal vein glucose concentration, the failure of HAL to result in enhanced NHGU during peripheral glucose infusion suggests the existence of one or more comparison sites outside the liver.