Based on our earlier work, a 2.5-fold increase in insulin secretion should completely inhibit hepatic glucose production through the hormone's direct effect on hepatic glycogen metabolism. The aim of the present study was to test the accuracy of this prediction and to confirm that gluconeogenic flux, as measured by three independent techniques, was unaffected by the increase in insulin. A 40-min basal period was followed by a 180-min experimental period in which an increase in insulin was induced, with euglycemia maintained by peripheral glucose infusion. Arterial and hepatic sinusoidal insulin levels increased from 10 ؎ 2 to 19 ؎ 3 and 20 ؎ 4 to 45 ؎ 5 U/ml, respectively. Net hepatic glucose output decreased rapidly from 1.90 ؎ 0.13 to 0.23 ؎ 0.16 mg ⅐ kg ؊1 ⅐ min ؊1 . Three methods of measuring gluconeogenesis and glycogenolysis were used: 1) the hepatic arteriovenous difference technique (n ‫؍‬ 8), 2) the [ (1) showed that hepatic glucose production (HGP) can be inhibited by selective increases in the arterial or portal vein insulin concentration. In response to a 14-U/ml increase in arterial insulin (no change in portal insulin), a Ͼ50% reduction in net hepatic glucose output (NHGO) was observed. Likewise, a 14-U/ml increase in portal insulin (no change in arterial insulin) also resulted in a Ͼ50% reduction in NHGO. In addition, the above studies showed that insulin acted directly on the liver, with a rise in hepatic sinusoidal insulin quickly inhibiting HGP by reducing net hepatic glycogenolysis. The indirect effect of insulin on HGP, on the other hand, resulted from a decrease in gluconeogenic flux rate caused by a reduction in the flow of gluconeogenic amino acids and glycerol to the liver and diversion of carbon derived from glycogenolysis to lactate rather than glucose. The reduction in HGP in this group was also, in part, the result of a decrease in net hepatic glycogenolysis, which occurred as a result of a slight rise in the hepatic sinusoidal insulin level, which, in turn, occurred as a result of the rise in hepatic artery insulin. It took 1 h to detect a significant indirect effect of insulin on HGP.Sindelar et al.(1) created selective changes in the arterial or portal insulin level by infusing somatostatin to inhibit insulin secretion and replacing insulin by infusion through a peripheral and/or portal catheter. Stimulation of pancreatic insulin secretion, on the other hand, results in an increase in both portal and arterial levels of the hormone. Therefore, in the present study, our aim was to determine if a two-to threefold increase in insulin, occurring simultaneously in portal and peripheral blood, would inhibit HGP primarily through an effect on glycogen metabolism. Although Sindelar et al. (1) reported that portally delivered insulin did not affect gluconeogenic flux, their estimate of the latter relied solely on the measurement of the net hepatic uptake (arteriovenous [AV] difference) of gluconeogenic precursors. In the present study, we combined the hepatic AV difference technique, along...

.-The aim of this study was to determine the effect of high levels of free fatty acids (FFA) and/or hyperglycemia on hepatic glycogenolysis and gluconeogenesis. Intralipid was infused peripherally in 18-h-fasted conscious dogs maintained on a pancreatic clamp in the presence (FFA ϩ HG) or absence (FFA ϩ EuG) of hyperglycemia. In the control studies, Intralipid was not infused, and euglycemia (EuG) or hyperglycemia (HG) was maintained. Insulin and glucagon were clamped at basal levels in all four groups. The arterial blood glucose level increased by 50% in the HG and FFA ϩ HG groups. It did not change in the EuG and FFA ϩ EuG groups. Arterial plasma FFA increased by ϳ140% in the FFA ϩ EuG and FFA ϩ HG groups but did not change significantly either in the EuG or HG groups. Arterial glycerol levels increased by ϳ150% in both groups. Overall (3-h) net hepatic glycogenolysis was 196 Ϯ 26 mg/kg in the EuG group. It decreased by 96 Ϯ 20, 82 Ϯ 16, and 177 Ϯ 22 mg/kg in the HG, FFA ϩ EuG, and FFA ϩ HG groups, respectively. Overall (3-h) hepatic gluconeogenic flux was 128 Ϯ 22 mg/kg in the EuG group, but it was suppressed by 30 Ϯ 9 mg/kg in response to hyperglycemia. It was increased by 59 Ϯ 12 and 56 Ϯ 10 mg/kg in the FFA ϩ EuG and FFA ϩ HG groups, respectively. In conclusion, an increase in plasma FFA and glycerol significantly inhibited hepatic glycogenolysis and markedly stimulated hepatic gluconeogenesis.free fatty acid; hyperglycemia; glycogenolysis; gluconeogenesis AN INCREASE IN FREE FATTY ACIDS (FFA) stimulates hepatic gluconeogenesis (10,14,37). In vitro studies have shown that perfusion of rat liver with lipid increases gluconeogenesis (36,37) and that an increase in FFA oxidation stimulates the activities of key enzymes in the gluconeogenic pathway (3,26). In accord with this, Boden and Jadali (5) reported that a rise in plasma FFA increased hepatic glucose production (HGP) in normal human subjects. In addition, Saloranta et al. (30) showed that an increase in FFA and glycerol availability, brought about by Intralipid infusion, increased gluconeogenesis and glucose production in type 2 diabetic patients. In contrast, in a recent study, Roden et al. (27) did not detect a change in HGP in response to an increase in FFA in normal humans. Likewise, Johnston et al. (18) reported that an acute increase in the plasma FFA level did not change HGP in type 2 diabetic subjects. In agreement with the latter, Puhakainen and colleagues (24,25) showed that a decrease in plasma FFA, although it reduced gluconeogenesis, did not change HGP in patients with type 2 diabetes. Most recently, Boden et al. (4) showed in both normal and type 2 diabetic subjects that increasing and decreasing plasma FFA stimulated and inhibited gluconeogenesis, respectively, but did not alter glucose production. In another recent study, Stingl et al. (35) showed that in normal humans HGP and glycogenolysis both decreased in response to an increase in plasma FFA level. It is obvious from the above discordance that the effect of an increase in FFA av...

The responses of the pancreatic ␣-and ␤-cells to small changes in glucose were examined in overnight-fasted conscious dogs. Each study consisted of an equilibration (-140 to -40 min), a control (-40 to 0 min), and a test period (0 to 180 min), during which BAY R3401 (10 mg/kg), a glycogen phosphorylase inhibitor, was administered orally, either alone to create mild hypoglycemia or with peripheral glucose infusion to maintain euglycemia or create mild hyperglycemia. Drug administration in the hypoglycemic group decreased net hepatic glucose output (NHGO) from 8.9 ± 1.7 (basal) to 6.0 ± 1.7 and 5.8 ± 1.0 µmol · kg -1 · min -1 by 30 and 90 min. As a result, the arterial plasma glucose level decreased from 5.8 ± 0.2 (basal) to 5.2 ± 0.3 and 4.4 ± 0.3 mmol/l by 30 and 90 min, respectively (P < 0.01). Arterial plasma insulin levels and the hepatic portalarterial difference in plasma insulin decreased (P < 0.01) from 78 ± 18 and 90 ± 24 to 24 ± 6 and 12 ± 12 pmol/l over the first 30 min of the test period and decreased to 18 ± 6 and 0 pmol/l by 90 min, respectively. The arterial glucagon levels and the hepatic portal-arterial difference in plasma glucagon increased from 43 ± 5 and 4 ± 2 to 51 ± 5 and 10 ± 5 ng/l by 30 min (P < 0.05) and to 79 ± 16 and 31 ± 15 ng/l by 90 min (P < 0.05), respectively. In euglycemic dogs, the arterial plasma glucose level remained at 5.9 ± 0.1 mmol/l, and the NHGO decreased from 10 ± 0.6 to -3.3 ± 0.6 µmol · kg -1 · min -1 (180 min). The insulin and glucagon levels and the hepatic portal-arterial differences remained constant. In hyperglycemic dogs, the arterial plasma glucose level increased from 5.9 ± 0.2 to 6.2 ± 0.2 mmol/l by 30 min, and the NHGO decreased from 10 ± 1.7 to 0 µmol · kg -1 · min -1 by 30 min. The arterial plasma insulin levels and the hepatic portal-arterial difference in plasma insulin increased from 60 ± 18 and 78 ± 24 to 126 ± 30 and 192 ± 42 pmol/l by 30 min, after which they averaged 138 ± 24 and 282 ± 30 pmol/l, respectively. The arterial plasma glucagon levels and the hepatic portal-arterial difference in plasma glucagon decreased slightly from 41 ± 7 and 4 ± 3 to 34 ± 7 and 3 ± 2 ng/l during the test period. These data show that the ␣-and ␤-cells of the pancreas respond as a coupled unit to very small decreases in the plasma glucose level. Diabetes 50:367-375, 2001 G lucagon secretion increases in response to a decrease in the plasma glucose concentration and decreases in response to a rise in the plasma glucose level. Furthermore, insulin has been postulated to exert a paracrine influence on glucagon secretion when its release is modified in response to changes in the plasma glucose concentration. To date, studies have not provided a complete understanding of the relationship between a decrement in the plasma glucose level and glucagon or insulin secretion, because the insulin level itself has been elevated to decrease the glucose level, and insulin per se can affect not only its own secretion (1), but also the release of other counterregulatory hormones, inclu...

The role of alpha- and beta-adrenergic receptor subtypes in mediating the actions of catecholamines on hepatic glucose production (HGP) was determined in sixteen 18-h-fasted conscious dogs maintained on a pancreatic clamp with basal insulin and glucagon. The experiment consisted of a 100-min equilibration, a 40-min basal, and two 90-min test periods in groups 1 and 2, plus a 60-min third test period in groups 3 and 4. In group 1 [alpha-blockade with norepinephrine (alpha-blo+NE)], phentolamine (2 microg x kg(-1) x min(-1)) was infused portally during both test periods, and NE (50 ng x kg(-1) x min(-1)) was infused portally at the start of test period 2. In group 2, beta-blockade with epinephrine (beta-blo+EPI), propranolol (1 microg x kg(-1) x min(-1)) was infused portally during both test periods, and EPI (8 ng x kg(-1) x min(-1)) was infused portally during test period 2. In group 3 (alpha(1)-blo+NE), prazosin (4 microg x kg(-1) x min(-1)) was infused portally during all test periods, and NE (50 and 100 ng x kg(-1) x min(-1)) was infused portally during test periods 2 and 3, respectively. In group 4 (beta(2)-blo+EPI), butoxamine (40 microg x kg(-1) x min(-1)) was infused portally during all test periods, and EPI (8 and 40 ng x kg(-1) x min(-1)) was infused portally during test periods 2 and 3, respectively. In the presence of alpha- or alpha(1)-adrenergic blockade, a selective rise in hepatic sinusoidal NE failed to increase net hepatic glucose output (NHGO). In a previous study, the same rate of portal NE infusion had increased NHGO by 1.6 +/- 0.3 mg x kg(-1) x min(-1). In the presence of beta- or beta(2)-adrenergic blockade, the selective rise in hepatic sinusoidal EPI caused by EPI infusion at 8 ng x kg(-1) x min(-1) also failed to increase NHGO. In a previous study, the same rate of EPI infusion had increased NHGO by 1.6 +/- 0.4 mg x kg(-1) x min(-1). In conclusion, in the conscious dog, the direct effects of NE and EPI on HGP are predominantly mediated through alpha(1)- and beta(2)-adrenergic receptors, respectively.

Experiments were performed on two groups of 42-h-fasted conscious dogs ( n = 6/group). Somatostatin was given peripherally with insulin (4-fold basal) and glucagon (basal) intraportally. In the first experimental period, glucose was infused peripherally to double the hepatic glucose load (HGL) in both groups. In the second experimental period, glucose (21.8 μmol ⋅ kg−1 ⋅ min−1) was infused intraportally and the peripheral glucose infusion rate (PeGIR) was reduced to maintain the precreating HGL in the portal signal (PO) group, whereas saline was given intraportally in the control (CON) group and PeGIR was not changed. In the third period, the portal glucose infusion was stopped in the PO group and PeGIR was increased to sustain HGL. PeGIR was continued in the CON group. The glucose loads to the liver did not differ in the CON and PO groups. Net hepatic glucose uptake was 9.6 ± 2.5, 11.6 ± 2.6, and 15.5 ± 3.2 vs. 10.8 ± 1.8, 23.7 ± 3.0, and 15.5 ± 1.1 μmol ⋅ kg−1 ⋅ min−1, and nonhepatic glucose uptake (non-HGU) was 29.8 ± 1.1, 40.1 ± 4.5, and 49.5 ± 4.0 vs. 26.6 ± 4.3, 23.2 ± 4.0, and 40.4 ± 3.1 μmol ⋅ kg−1 ⋅ min−1in the CON and PO groups during the three periods, respectively. Cessation of the portal signal shifted NHGU and non-HGU to rates similar to those evident in the CON group within 10 min. These results indicate that even under hyperinsulinemic conditions the effects of the portal signal on hepatic and peripheral glucose uptake are rapidly reversible.