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The objective of this study was to assess the response of a large animal model to high dietary fat and fructose (HFFD). Three different metabolic assessments were performed during 13 wk of feeding an HFFD (n = 10) or chow control (CTR, n = 4) diet: oral glucose tolerance tests (OGTTs; baseline, 4 and 8 wk), hyperinsulinemic-euglycemic clamps (HIEGs; baseline and 10 wk) and hyperinsulinemic-hyperglycemic clamps (HIHGs, 13 wk). The [DELTA]AUC for glucose during the OGTTs more than doubled after 4 and 8 wk of HFFD feeding, and the average glucose infusion rate required to maintain euglycemia during the HIEG clamps decreased by [approximately equal to]30% after 10 wk of HFFD feeding. These changes did not occur in the CTR group. The HIHG clamps included experimental periods 1 (P1, 0-90 min) and 2 (P2, 90-180 min). During P1, somatostatin, basal intraportal glucagon, 4 x basal intraportal insulin, and peripheral glucose (to double the hepatic glucose load) were infused; during P2, glucose was also infused intraportally (4.0 mg x [kg.sup.-1] x [min.sup.-1]). Net hepatic glucose uptake during P1 and P2 was -0.4 [+ or -] 0.1 [output] and 0.2 [+ or -] 0.8 mg x [kg.sup.-1] x [min.sup.-1] in the HFFD group, respectively, and 1.8 [+ or -] 0.8 and 3.5 [+ or -] 1.0 mg x [kg.sup.-1] x [min.sup.-1] in the CTR group, respectively (P < 0.05 vs. HFFD during P1 and P2). Glycogen synthesis through the direct pathway was 0.5 [+ or -] 0.2 and 1.5 [+ or -] 0.4 mg x [kg.sup.-1] x [min.sup.-1] in the HFFD and CTR groups, respectively (P < 0.05 vs. HFFD). In conclusion, chronic consumption of an HFFD diminished the sensitivity of the liver to hormonal and glycemic cues and resulted in a marked impairment in NHGU and glycogen synthesis. impaired glucose tolerance; glycogen synthesis; hyperinsulinemic euglycemic clamp; hyperinsulinemic hyperglycemic clamp; portal signal doi: 10.1152/ajpendo.00372.2010.

We examined whether intraportal delivery of neuropeptide Y (NPY) affects glucose metabolism in 42-h-fasted conscious dogs using arteriovenous difference methodology. The experimental period was divided into three subperiods (P1, P2, and P3). During all subperiods, the dogs received infusions of somatostatin, intraportal insulin (threefold basal), intraportal glucagon (basal), and peripheral intravenous glucose to increase the hepatic glucose load twofold basal. Following P1, in the NPY group (n = 7), NPY was infused intraportally at 0.2 and 5.1 pmo1*[kg.sup.-1]*[min.sup.-1] during P2 and P3, respectively. The control group (n = 7) received intraportal saline infusion without NPY. There were no significant changes in hepatic blood flow in NPY vs. control. The lower infusion rate of NPY (P2) did not enhance net hepatic glucose uptake. During P3, the increment in net hepatic glucose uptake (compared with P1) was 4 [+ or -] 1 and 10 [+ or -] 2 [micro]mol*[kg.sup.-1]*[min.sup.-1] in control and NPY, respectively (P < 0.05). The increment in net hepatic fractional glucose extraction during P3 was 0.015 [+ or -] 0.005 and 0.039 [+ or -] 0.008 in control and NPY, respectively (P < 0.05). Net hepatic carbon retention was enhanced in NPY vs. control (22 [+ or -] 2 vs. 14 [+ or -] 2 [micro]mol*[kg.sup.-1]*[min.sup.-1], P < 0.05). There were no significant differences between groups in the total glucose infusion rate. Thus, intraportal NPY stimulates net hepatic glucose uptake without significantly altering whole body glucose disposal in dogs. dog; liver; nerves

Hepatic portal venous infusion of nitric oxide synthase (NOS) inhibitors causes muscle insulin resistance, but the effects on hepatic glucose disposition are unknown. Conscious dogs underwent a hyperinsulinemic (4-fold basal) hyperglycemic (hepatic glucose load 2-fold basal) clamp, with assessment of liver metabolism by arteriovenous difference methods. After 90 min (P1), dogs were divided into two groups: control (receiving intraportal saline infusion, n = 8) and LN [receiving [N.sup.G]-nitro-Larginine methyl ester (L-NAME), a nonspecific NOS inhibitor; n = 11] intraportally at 0.3 mg * [kg.sup.-1] * [min.sub.-1] for 90 rain (P2). During the final 60 min of study (P3), L-NAME was discontinued, and five LN dogs received the NO donor SIN-1 intraportally at 6 [micro]g * [kg.sup.-1] * [min.sup.-1] while six received saline (LN/SIN-1 and LN/SAL, respectively). Net hepatic fractional glucose extraction (NHFE) in control dogs was 0.034 [+ or -] 0.016, 0.039 [+ or -] 0.015, and 0.056 [+ or -] 0.019 during P1, P2, and P3, respectively. NHFE in LN was 0.045 [+ or -] 0.009 and 0.111 [+ or -] 0.007 during P1 and P2, respectively (P < 0.05 vs. control during P2), and 0.087 [+ or -] 0.009 and 0.122 [+ or -] 0.016 (P < 0.05) during P3 in LN/SIN-1 and LN/SAL, respectively. During P2, arterial glucose was 204 [+ or -] 5 vs. 138 [+ or -] 11 mg/dl (P < 0.05) in LN vs. control to compensate for L-NAME's effect on blood flow. Therefore, another group (LNlow; n = 4) was studied in the same manner as LN/SAL, except that arterial glucose was clamped at the same concentrations as in control. NHFE in LNlow was 0.052 [+ or -] 0.008, 0.093 [+ or -] 0.023, and 0.122 [+ or -] 0.021 during P1, P2, and P3, respectively (P < 0.05 vs. control during P2 and P3), with no significant difference in glucose infusion rates. Thus, NOS inhibition enhanced NI-IFE, an effect partially reversed by SIN-1. [N.sup.G]nitro-L-arginine methyl ester; 3-morpholynosydnonimine; dog

To determine the role of nitric oxide in regulating net hepatic glucose uptake (NHGU) in vivo, studies were performed on three groups of 42-h-fasted conscious dogs using a nitric oxide donor [beta]-morpholinosydnonimine (SIN-I)]. The experimental period was divided into period 1 (0-90 rain) and period 2 (P2; 90-240 min). At 0 min, somatostatin was infused peripherally, and insulin (4-fold basal) and glucagon (basal) were given intraportally. Glucose was delivered intraportally (22.2 [micro]mol*[kg.sup.-1]*[min.sup.-1]) and peripherally (as needed) to increase the hepatic glucose load twofold basal. At 90 min, an infusion of SIN-1 (4 [micro]mol*[kg.sup.-1]*[min.sup.-1]) was started in a peripheral vein (PeSin-1, n = 10) or the portal vein (PoSin-1, n = 12) while the control group received saline (SAL, n = 8). Both peripheral and portal infusion of SIN-1, unlike saline, significantly reduced systolic and diastolic blood pressure. Heart rate rose in PeSin-1 and PoSin-1 (96 [+ or -] 5 to 120 [+ or -] 10 and 88 [+ or -] 6 to 107 [+ or -] 5 beats/min, respectively, P < 0.05) but did not change in response to saline. NHGU during P2 was 31.0 [+ or -] 2.4 and 29.9 [+ or -] 2.0 [micro]mol*[kg.sup.-1]*[min.sup.-1] in SAL and PeSin-1, respectively but was 23.7 [+ or -] 1.7 in PoSin-1 (P < 0.05). Net hepatic carbon retention during P2 was significantly lower in PoSin-1 than SAL or PeSin-1 (21.4 [+ or -] 1.2 vs. 27.1 [+ or -] 1.5 and 26.1 [+ or -] 1.0 [micro]mol*[kg.sup.-1]*[min.sup.-1]). Nonhepatic glucose uptake did not change in response to saline or SIN-1 infusion. In conclusion, portal but not peripheral infusion of the nitric oxide donor SIN-1 inhibited NHGU. 3-morpholinosydnominine; nitric oxide; net hepatic glucose uptake; hyperglycemia

Portal glucose delivery enhances net hepatic glucose uptake (NHGU) relative to peripheral glucose delivery. We hypothesize that the sympathetic nervous system normally restrains NHGU, and portal glucose delivery relieves the inhibition. Two groups of 42-h-fasted conscious dogs were studied using arteriovenous difference techniques. Denervated dogs (DEN; n = 10) underwent selective sympathetic denervation by cutting the nerves at the celiac nerve bundle near the common hepatic artery; control dogs (CON; n = 10) underwent a sham procedure. After a 140-min basal period, somatostatin was given along with basal intraportal infusions of insulin and glucagon. Glucose was infused peripherally to double the hepatic glucose load (HGL) for 90 min (P1). In P2, glucose was infused intraportally (3-4 mg x [kg.sup.-1] x [min.sup.-1]), and the peripheral glucose infusion was reduced to maintain the HGL for 90 min. This was followed by 90 min (P3) in which portal glucose infusion was terminated and peripheral glucose infusion was increased to maintain the HGL. P1 and P3 were averaged as the peripheral glucose infusion period (PE). The average HGLs (mg x [kg.sup.-1] x [min.sup.-1]) in CON and DEN were 55 [+ or -] 3 and 54 [+ or -] 4 in the peripheral periods and 55 [+ or -] 3 and 55 [+ or -] 4 in P2, respectively. The arterial insulin and glucagon levels remained basal in both groups. NHGU (mg x [kg.sup.-1] x [min.sup.-1]) in CON averaged 1.7 [+ or -] 0.3 during PE and increased to 2.9 [+ or -] 0.3 during P2. NHGU (mg x [kg.sup.-1] x [min.sup.-1]) was greater in DEN than CON (P < 0.05) during PE (2.9 [+ or -] 0.4) and failed to increase significantly (3.2 [+ or -] 0.2) during P2 (not significant vs. CON). Selective sympathetic denervation increased NHGU during hyperglycemia but significantly blunted the response to portal glucose delivery. autonomic nervous system; liver; canine

Whether glucagon-like peptide (GLP)-1 requires the hepatic portal vein to elicit its insulin secretion-independent effects on glucose disposal in vivo was assessed in conscious dogs using tracer and arteriovenous difference techniques. In study 1, six conscious overnight-fasted dogs underwent oral glucose tolerance testing (OGTT) to determine target GLP-1 concentrations during clamp studies. Peak arterial and portal values during OGTT ranged from 23 to 65 pM and from 46 to 113 pM, respectively. In study 2, we conducted hyperinsulinemic-hyperglycemic clamp experiments consisting of three periods (P1, P2, and P3) during which somatostatin, glucagon, insulin and glucose were infused. The control group received saline, the PePe group received GLP-1 (1 pmol x [kg.sup.-1] x [min.sup.-1]) peripherally, the PePe group received GLP-1 (1 pmol x [kg.sup.-1] x [min.sup.-1]) peripherally (P2) and then intraportally (P3), and the PeHa group received GLP-1 (1 pmol x [kg.sup.-1] x [min.sup.-1]) peripherally (P2) and then through the hepatic artery (P3) to increase the hepatic GLP-1 load to the same extent as in P3 in the PePo group (n = 8 dogs/group). Arterial GLP-1 levels increased similarly in all groups during P2 (~50 [micro]M), whereas portal GLP-1 levels were significantly increased (2-fold) in the PePo vs. PePe and PeHa groups during P3. During P2, net hepatic glucose uptake (NHGU) increased slightly but not significantly (vs. P1) in all groups. During P3, GLP-1 increased NHGU in the PePo and PeHa groups more than in the control and PePe groups (change of 10.8 [+ or -] 1.3 and 10.6 [+ or -] 1.0 vs. 5.7 [+ or -] 1.0 and 5.4 [+ or -] 0.8 [micro]mol x [kg.sup.-1] x [min.sup.-1], respectively, P < 0.05). In conclusion, physiological GLP-1 levels increase glucose disposal in the liver, and this effect does not involve GLP-1 receptors located in the portal vein. glucose uptake; dog; oral glucose tolerance test; glucagon-like peptide-1

The effect of small amounts of fructose on net hepatic glucose uptake (NHGU) during hyperglycemia was examined in the presence of insulinopenia in conscious 42-h fasted dogs. During the study, somatostatin (0.8 [micro]*g[kg.sup.-1] * [min.sup.-1]) was given along with basal insulin (1.8 pmol*[kg.sup.-1] * [min.sup.-1]) and glucagon (0.5 ng*[kg.sup.-1] * [min.sup.-1]). After a control period, glucose (36.1 [micro]mol*[kg.sup.-l]*[min.sup.-1]) was continuously given intraportally for 4 h with (2.2 [micro]mol*[kg.sup.-l]*[min.sup.-1]) or without fructose. In the fructose group, the sinusoidal blood fructose level (nmol/ml) rose from < 16 to 176 [+ or -] 11. The infusion of glucose alone (the control group) elevated arterial blood glucose ([micro]mol/ml) from 4.3 [+ or -] 0.3 to 11.2 [+ or -] 0.6 during the first 2 h after which it remained at 11.6 [+ or -] 0.8. In the presence of fructose, glucose infusion elevated arterial blood glucose ([micro]mol/ml) from 4.3 [+ or -] 0.2 to 7.4 [+ or -] 0.6 during the first 1 h after which it decreased to 6.1 [+ or -] 0.4 by 180 min. With glucose infusion, net hepatic glucose balance ([micro]mol*[kg.sup.-l]* [min.sup.-1]) switched from output (8.9 [+ or -] 1.7 and 13.3 [+ or -] 2.8) to uptake (12.2 [+ or -] 4.4 and 29.4 [+ or -] 6.7) in the control and fructose groups, respectively. Average NHGU ([micro]mol*[kg.sup.-l] *[min.sup.-1]) and fractional glucose extraction (%) during last 3 h of the test period were higher in the fructose group (30.6 [+ or -] 3.3 and 14.5 [+ or -] 1.4) than in the control group (15.0 [+ or -] 4.4 and 5.9 [+ or -] 1.8). Glucose 6-phosphate and glycogen content ([micro]mol glucose/g) in the liver and glucose incorporation into hepatic glycogen ([micro]mol glucose/g) were higher in the fructose (218 [+ or -] 2, 283 [+ or -] 25, and 109 [+ or -] 26, respectively) than in the control group (80 [+ or -] 8,220 [+ or -] 31, and 41 [+ or -] 5, respectively). In conclusion, small amounts of fructose can markedly reduce hyperglycemia during intraportal glucose infusion by increasing NHGU even when insulin secretion is compromised. diabetes mellitus; hyperglycemia; hyperinsulinemia

Moore, Mary Courtney, Catherine A. DiCostanzo, Dominique Dardevet, Margaret Lautz, Ben Farmer, Doss W. Neal, and Alan D. Cherrington. Portal infusion of a selective serotonin reuptake inhibitor enhances hepatic glucose disposal in conscious dogs. Am J Physiol Endocrinol Metab 287: E1057-E1063, 2004. First published August 17, 2004; doi:10.1152/ajpendo.00313.2004.--Intraportal delivery of serotonin enhanced net hepatic glucose uptake (NHGU) during a hyperinsulinemic hyperglycemic clamp, but serotonin elevated catecholamines and can cause gastrointestinal distress. We hypothesized that the selective serotonin reuptake inhibitor (SSRI) fluvoxamine would enhance NHGU without side effects. Arteriovenous difference and tracer ([[3.sup.-3]H]glucose) techniques were used in conscious 42-h-fasted dogs. Experiments consisted of equilibration (-120 to -30 min), basal (-30 to 0 min), and experimental (EXP; 0-270 min) periods. During EXP, somatostatin, fourfold basal intraportal insulin, basal intraportal glucagon, and peripheral glucose (to double the hepatic glucose load) were infused. Saline (SAL) was infused intraportally during 0-90 min (P1), and fluvoxamine was infused intraportally at 0.5, 1, and 2 [micro]g x [kg.sup.-1] x [min.sup.-1] from 90 to 150 (P2), 150 to 210 (P3), and 210 to 270 (P4) min, respectively, in the FLUV group (n = 8). The SAL group (n = 9) received intraportal saline during 0-270 min. NHGU in SAL was 13.9 [+ or -] 1.7 and 17.0 [+ or -] 2.0 [micro]mol x [kg.sup.-1] x [min.sup.-1] in P3-P4, respectively, while NHGU in FLUV averaged 19.7 [+ or -] 2.8 and 26.6 [+ or -] 3.0 [micro]mol x [kg.sup.-1] x [min.sup.-1] (P < 0.05 vs. SAL). Net hepatic carbon retention was greater (P < 0.05) in FLUV than in SAL (17.6 [+ or -] 2.6 vs. 13.9 [+ or -] 2.7 and 23.8 [+ or -] 3.0 vs. 14.4 [+ or -] 3.3 [micro]mol x [kg.sup.-1] x [min.sup.-1] in P3-P4, respectively), and final hepatic glycogen concentrations were 50% greater in FLUV (P < 0.005). Nonhepatic glucose uptake was greater in SAL than in FLUV at 270 min (P < 0.05). Catecholamine concentrations remained basal, and the animals evidenced no distress. Thus fluvoxamine enhanced NHGU and hepatic carbon storage without raising circulating serotonin concentrations or causing stress, suggesting that hepatic-targeted SSRIs might be effective in reducing postprandial hyperglycemia in individuals with diabetes or impaired glucose tolerance. glycemia; liver; portal vein; hepatic glucose uptake; nonhepatic glucose uptake

Vagal cooling and concomitant portal norepinephrine infusion do not reduce net hepatic glucose uptake in conscious dogs. Am J Physiol Regul Integr Comp Physiol 287: R742-R748, 2004. First published May 27, 2004; 10.1152/ ajpregu.00041.2004.--We examined the role of efferent neural signaling in regulation of net hepatic glucose uptake (NHGU) in two groups of conscious dogs with hollow perfusable coils around their vagus nerves, using tracer and arteriovenous difference techniques. Somatostatin, intraportal insulin and glucagon at fourfold basal and basal rates, and intraportal glucose at 3.8 mg*[kg.sup.-1]*[min.sup.-1] were infused continuously. From 0 to 90 min [period 1 (P1], the coils were perfused with a 37[degrees]C solution. During period 2 [P2; 90-150 min in group 1 (n = 3); 90-180 min in group 2 (n = 6)], the coils were perfused with -15[degrees]C solution to eliminate vagal signaling, and the coils were subsequently perfused with 37[degrees]C solution during period 3 (P3). In addition, group 2 received an intraportal infusion of norepinephrine at 16 ng*[kg.sup.-1]*[min.sup.-1] during P2. The effectiveness of vagal suppression was demonstrated by the increase in heart rate during P2 (111 [+ or -] 17, 167 [+ or -] 16, and 105 [+ or -] 13 beats/min in group 1 and 71 [+ or -] 6, 200 [+ or -] 11, and 76 [+ or -] 6 beats/min in group 2 during P1-P3, respectively) and by prolapse of the third eyelid during P2. Arterial plasma glucose, insulin, and glucagon concentrations; hepatic blood flow; and hepatic glucose load did not change significantly during P1-P3. NHGU during P1-P3 was 2.7 [+ or -] 0.4, 4.1 [+ or -] 0.6, and 4.0 [+ or -] 1.2 mg*[kg.sup.-1]*[min.sup.-1] in group 1 and 5.0 [+ or -] 0.9, 5.6 [+ or -] 0.7, and 6.1 [+ or -] 0.9 mg*[kg.sup.-1]*[min.sup.-1] in group 2 (not significant among periods). Interruption of vagal signaling with or without intraportal infusion of norepinephrine to augment sympathetic tone did not suppress NHGU during portal glucose delivery, suggesting the portal signal stimulates NHGU independently of vagal efferent flow. vagus nerve: efferent neural transmission

We recently compared the regulation of glucose-6-phosphatase (G-6-Pase) catalytic subunit and glucose 6-phosphate (G-6-P) transporter gene expression by insulin in conscious dogs in vivo (Hornbuckle LA, Edgerton DS, Ayala JE, Svitek CA, Neal DW, Cardin S, Cherrington AD, and O'Brien RM. Am J Physiol Endocrinol Metab 281: E713-E725, 2001). In pancreatic-clamped, euglycemic conscious dogs, a 5-h period of hypoinsulinemia led to a marked increase in hepatic G-6-Pase catalytic subunit mRNA; however, G-6-P transporter mRNA was unchanged. Here, we demonstrate, again using pancreatic-clamped, conscious dogs, that glucagon is a candidate for the factor responsible for this selective induction. Thus glucagon stimulated G-6-Pase catalytic subunit but not G-6-P transporter gene expression in vivo. Furthermore, cAMP stimulated endogenous G-6-Pase catalytic subunit gene expression in HepG2 cells but had no effect on G-6-P transporter gene expression. The cAMP response element (CRE) that mediates this induction was identified through transient transfection of HepG2 cells with G-6-Pase catalytic subunit-chloramphenicol acetyltransferase fusion genes. Gel retardation assays demonstrate that this CRE hinds several transcription factors including CRE-binding protein and CCAAT enhancer-binding protein. insulin; fatty acids; gene transcription; cyclic adenosine monophosphate; glucose-6-phosphatase; glucose 6-phosphate

Portal infusion of glucose in the mouse at a rate equivalent to basal endogenous glucose production causes hypoglycemia, whereas peripheral infusion at the same rate causes significant hyperglycemia. We used tracer and arteriovenous difference techniques in conscious 42-h-fasted dogs to determine their response to the same treatments. The studies consisted of three periods: equilibration (100 min), basal (40 min), and experimental (180 min), during which glucose was infused at 13.7 [micro]mol* [kg.sup.-1]*[min.sup.-1] into a peripheral vein (PE, n = 5) or the hepatic portal (PO, n = 5) vein. Arterial blood glucose increased ~0.8 mmol/l in both groups. Arterial and hepatic sinusoidal insulin concentrations were not significantly different between groups. PE exhibited an increase in nonhepatic glucose uptake (non-HGU; [DELTA]8.6 [+ or -] 1.2 [micro]mol*[kg.sup.-1]*[min.sup.-1]) within 30 min, whereas PO showed a slight suppression ([DELTA]-3.7 [+ or -] 3.1 [micro]mol*[kg.sup.-1]*[min.sup.-1]). PO shifted from net hepatic glucose output (NHGO) to uptake (NHGU; 2.5 [+ or -] 2.8 [micro]mol*[kg.sup.-1]*[min.sup.-1]) within 30 min, but PE still exhibited NHGO (6.0 [+ or -] 1.9 [micro]mol*[kg.sup.-1]*[min.sup.-1]) at that time and did not initiate NHGU until after 90 min. Glucose rates of appearance and disappearance did not differ between groups. The response to the two infusion routes was markedly different. Peripheral infusion caused a rapid enhancement of non-HGU, whereas portal delivery quickly activated NHGU. As a result, both groups maintained near-euglycemia. The dog glucoregulates more rigorously than the mouse in response to both portal and peripheral glucose delivery. hypoglycemia; hyperglycemia; portal vein; glucosensor

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 ([HAL.sub.po]) received intraportal glucose (3.8 mg*[kg.sup.-1]*[min.sup.-1]) and seven ([HAL.sub.pe]) 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 [HAL.sub.pe.] During period 2, the arterial plasma insulin concentrations (24 [+ or -] 3, 20 [+ or -] 1, and 24 [+ or -] 2 [micro]U/ml) and hepatic glucose loads (39.1 [+ or -] 2.5, 43.8 [+ or -] 2.9, and 37.7 [+ or -] 3.7 mg*[kg.sup.- 1]*[min.sup.-1]) were not different in [HAL.sub.pe], [HAL.sub.po], and control, respectively. [HAL.sub.po] exhibited greater (P < 0.05) NHGU than [HAL.sub.pe] and control (3.1 [+ or -] 0.3, 2.0 [+ or -] 0.4, and 2.0 [+ or -] 0.1 mg*[kg.sup.-1]*[min.sup.-1], respectively). Net hepatic carbon retention was approximately twofold greater (P < 0.05) in [HAL.sub.po] than in [HAL.sub.pe ]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. liver glucose uptake; portal vein

Arteriovenous difference and tracer ([3-[sup.3]H]glucose) techniques were used in 42-h-fasted conscious dogs to identify any insulin-like effects of intraportally administered glucagonlike peptide 1-(7-36)amide (GLP-1). Each study consisted of an equilibration, a basal, and three 90-min test periods (P1, P2, and P3) during which somatostatin, intraportal insulin (3-fold basal) and glucagon (basal), and peripheral glucose were infused. Saline was infused intraportally in P1. During P2 and P3, GLP-1 was infused intraportally at 0.9 and 5.1 pmol*[kg.sup.-1]* [min.sup.-1] in eight dogs, at 10 and 20 pmol*[kg.sup.-1]*[min.sup.-1] in seven dogs, and at 0 pmol*[kg.sup.-1]*[min.sup.-1] in eight dogs (control group). Net hepatic glucose uptake was significantly enhanced during GLP-1 infusion at 20 pmol*[kg.sup.-1]*[min.sup.-1] [21.8 vs. 13.4 [micro]mol* [kg.sup.-1]*[min.sup.-1] (control), P < 0.05]. Glucose utilization was significantly increased during infusion at 10 and 20 pmol*[kg.sup.-1] [min.sup.-1] [87.3 [+ or -] 8.3 and 105.3 [+ or -] 12.8, respectively, vs. 62.2 [+ or -] 5.3 and 74.7 [+ or -] 7.4 [micro]mol*[kg.sup.-1]*[min.sup.-1] (control), P < 0.05]. The glucose infusion rate required to maintain hyperglycemia was increased (P < 0.05) during infusion of GLP-1 at 5.1, 10, and 20 pmol*[kg.sup.-1]*[min.sup.-1] (22, 36, and 32%, respectively, greater than control). Nonhepatic glucose uptake increased significantly during delivery of GLP-1 at 5.1 and 10 pmol*[kg.sup.-1]*[min.sup.-1] (25 and 46% greater than control) and tended (P = 0.1) to increase during GLP-1 infusion at 20 pmol*[kg.sup.-1]*[min.sup.-1] (24% greater than control). Intraportal infusion of GLP-1 at high physiological and pharmacological rates increased glucose disposal primarily in nonhepatic tissues. incretin; net hepatic glucose uptake; muscle glucose uptake; blood glucose

To determine the effects of an increase in lipolysis on the glycogenolytic effect of epinephrine (EPI), the catecholamine was infused portally into 18-h-fasted conscious dogs maintained on a pancreatic clamp in the presence [portal (Po)-EPI+FFA, n = 6] and absence (Po-EPI+SAL, n = 6) of peripheral Intralipid infusion. Control groups with high glucose (70% increase) and free fatty acid (FFA; 200% increase; HG+FFA, n = 6) and high glucose alone (HG+SAL, n = 6) were also included. Hepatic sinusoidal EPI levels were elevated ([DELTA]568 [+ or -] 77 and [DELTA]527 [+ or -] 37 pg/ml, respectively) in Po-EPI+SAL and EPI+FFA but remained basal in HG+FFA and HG+SAL. Arterial plasma FFA increased from 613 [+ or -] 73 to 1,633 [+ or -] 101 and 746 [+ or -] 112 to 1,898 [+ or -] 237 [micro]mol/l in Po-EPI+FFA and HG+FFA but did not change in EPI+SAL or HG+SAL. Net hepatic glycogenolysis increased from 1.5 [+ or -] 0.3 to 3.1 [+ or -] 0.4 mg * [kg.sup.-1] * [min.sup.-1] (P < 0.05) by 30 min in response to portal EPI but did not rise (1.8 [+ or -] 0.2 to 2.1 [+ or -] 0.3 mg * [kg.sup.-1] * [min.sup.-1]) in response to Po-EPI+FFA. Net hepatic glycogenolysis decreased from 1.7 [+ or -] 0.2 to 0.9 [+ or -] 0.2 and 1.6 [+ or -] 0.2 to 0.7 [+ or -] 0.2 mg * [kg.sup.-1] * [min.sup.-1] by 30 min in HG+FFA and HG+SAL. Hepatic gluconeogenic flux to glucose 6-phosphate increased from 0.6 [+ or -] 0.1 to 1.2 [+ or -] 0.1 mg * [kg.sup.-1] * [min.sup.-1] (P < 0.05; by 3 h) and 0.7 [+ or -] 0.1 to 1.6 [+ or -] 0.1 mg * [kg.sup.-1] * [min.sup.-1] (P < 0.05; at 90 min) in HG+FFA and Po-EPI+FFA. The gluconeogenic parameters remained unchanged in the Po-EPI+SAL and HG+SAL groups. In conclusion, increased FFA markedly changed the mechanism by which EPI stimulated hepatic glucose production, suggesting that its overall lipolytic effect may be important in determining its effect on the liver. gluconeogenesis; glycogenolysis

We determined if blocking transmission in the fibers of the vagus nerves would affect basal hepatic glucose metabolism in the 18-h-fasted conscious dog. A pancreatic clamp (somatostatin, basal portal insulin, and glucagon) was employed. A 40-rain control period was followed by a 90-min test period. In one group, stainless steel cooling coils (Sham, n = 5) were perfused with a 37[degrees]C solution, while in the other (Cool, n = 6), the coils were perfused with -20[degrees]C solution. Vagal blockade was verified by heart rate change (80 [+ or -] 9 to 84 [+ or -] 14 beats/rain in Sham; 98 [ or -] + 12 to 193 [+ or -] 22 beats/min in Cool). The arterial glucose level was kept euglycemic by glucose infusion. No change in tracer-determined glucose production occurred in Sham, whereas in Cool it dropped significantly (2.4 [+ or -] 0.4 to 1.9 [+ or -] 0.4 mg*[kg.sup.-1]* [min.sup.-1]). Net hepatic glucose output did not change in Sham but decreased from 1.9 [+ or -] 0.3 to 1.3 [+ or -] 0.3 mg*[kg.sup.-1* [min.sup.-1] in the Cool group. Hepatic gluconeogenesis did not change in either group. These data suggest that vagal blockade acutely modulates hepatic glucose production by inhibiting glycogenolysis. vagal cooling; liver nerves; parasympathetic blockade; gluconeogenesis; glycogenolysis

Effects of free fatty acids on hepatic glycogenolysis and gluconeogenesis in conscious dogs. Am J Physiol Endocrinol Metab 282:E402-E411, 2002. First published October 10, 2001; 10.1152/ajpendo.00136. 2001.--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 + HG) or absence (FFA + 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 + HG groups. It did not change in the EuG and FFA + EuG groups. Arterial plasma FFA increased by ~140% in the FFA + EuG and FFA + HG groups but did not change significantly either in the EuG or HG groups. Arterial glycerol levels increased by ~150% in both groups. Overall (3-h) net hepatic glycogenolysis was 196 [+ or -] 26 mg/kg in the EuG group. It decreased by 96 [+ or -] 20, 82 [+ or -] 16, and 177 [+ or -] 22 mg/kg in the HG, FFA + EuG, and FFA + HG groups, respectively. Overall (3-h) hepatic gluconeogenic flux was 128 [+ or -] 22 mg/kg in the EuG group, but it was suppressed by 30 [+ or -] 9 mg/kg in response to hyperglycemia. It was increased by 59 [+ or -] 12 and 56 [+ or -] 10 mg/kg in the FFA + EuG and FFA + 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

Effect of hepatic denervation on peripheral insulin sensitivity in conscious dogs. Am J Physiol Endocrinol Metab 282: E286-E296, 2002; 10.1152/ajpendo.00201. 2001.--We tested the hypothesis that the loss of hepatic nerves decreases peripheral insulin sensitivity. Surgical hepatic denervation (DN) was performed in 22 dogs ~16 days before study; 7 dogs (Sham-Sal) had a sham procedure. A euglycemic hyperinsulinemic (1 mU * [kg.sup.-1] * [min.sup.-1]; arterial insulin 35 [+ or -] 1 [micro]U/ml in all dogs) clamp was performed in conscious dogs. From 0 to 90 min of the clamp, all dogs received the same treatment; then the DN dogs were divided into three groups. From 90 to 180 min, DN-PeA (n = 7) and DN-PoA (n = 7) groups received acetylcholine 2.5 [micro]g * [kg.sup.-1] * [min.sup.-1] via peripheral or portal vein, respectively, and DN-Sal (n = 8) received no acetylcholine. During 150-180 min, the Sham-Sal, DN-Sal, DN-PeA, and DN-PoA groups exhibited glucose infusion rates of 12.4 [+ or -] 0.8, 9.3 [+ or -] 0.8 (P < 0.05 vs. Sham-Sal), 9.1 [+ or -] 0.1 (P < 0.05 vs. Sham-Sal), and 12.7 [+ or -] 1.6 mg * [kg.sup.-1] * [min.sup.-1]; nonhepatic glucose uptakes of 11.5 [+ or -] 0.9, 8.9 [+ or -] 0.7 (P < 0.05 vs. Sham-Sal), 8.6 [+ or -] 0.9 (P < 0.05 vs. Sham-Sal), and 11.9 [+ or -] 1.7 mg * [kg.sup.-1] * [min.sup.-1]; net hindlimb glucose uptakes of 18.4 [+ or -] 2.1, 13.7 [+ or -] 1.1 (P < 0.05 vs. Sham-Sal), 17.5 [+ or -] 1.9, and 16.7 [+ or -] 3.2 mg/min; and glucose utilization rates of 14.4 [+ or -] 1.4, 10.4 [+ or -] 0.8 (P < 0.05 vs. Sham-Sal), 9.8 [+ or -] 0.9 (P < 0.05 vs. Sham-Sal), and 13.6 [+ or -] 1.8 mg * [kg.sup.-1] * [min.sup.-1], respectively. DN caused peripheral insulin resistance, and intraportal but not peripheral acetylcholine restored insulin sensitivity. hepatic nerves; acetylcholine

These studies were conducted to determine the effect of route of gluconeogenic amino acid delivery on the hepatic uptake of the amino acids. After a sampling period with no experimental intervention (basal period), conscious dogs deprived of food for 42 h received somatostatin, intraportal infusions of insulin (3-fold basal) and glucagon (basal), and a peripheral infusion of glucose to increase the hepatic glucose load 1.5-fold basal for 240 min. A mixture of alanine, glutamate, glutamine, glycine, serine and threonine was infused intraportally at 7.6 (mu)mol * kg(super -1) * min(super -1) (PorAA group, n = 6) or peripherally at 8.1 (mu)mol * kg(super -1) * min(super -1) (PerAA, n = 6), to match the hepatic load of gluconeogenic amino acids in PorAA. During the infusion period, there were no differences in PerAA and PorAA, respectively, with regard to arterial plasma insulin (144 +/- 18 and 162 +/- 18 pmol/L), glucagon (51 +/- 8 and 47 +/- 11 ng/L), hepatic glucose load (199.8 +/- 22.2 and 210.9 +/- 16.6 (mu)mol * kg(super -1) * min(super -1), net hepatic glucose uptake (2.8 +/- 2.2 and 2.2 +/- 1.7 (mu)mol * kg(super -1) * min(super -1), hepatic load of amino acids (68 +/- 14 and 62 +/- 7 (mu)mol * kg(super -1) * min(super -1), or net hepatic glycogen synthesis (11.1 +/- 2.2 and 8.9 +/- 2.2 (mu)mol * kg(super -1) * min(super -1)). The net hepatic uptake of glutamine (2.1 +/- 0.4 vs. 0.8 +/- 0.3 (mu)mol * kg(super -1) * min(super -1)) and the net hepatic fractional extractions of glutamine (0.11 +/- 0.02 vs. 0.05 +/- 0.02) and serine (0.41 +/- 0.03 vs. 0.34 +/- 0.02) were greater in PorAA than in PerAA (P < 0.05). We speculate that one or more of the amino acids in the mixture causes enhancement of the net hepatic uptake and fractional extraction of glutamine, and perhaps other gluconeogenic amino acids, during intraportal amino acid delivery.

Net hepatic glucose uptake (NHGU) and the suppression of muscle glucose uptake caused by the portal signal under under hyperglycemic conditions have been studied under euglycemic conditions. Twenty 42-hour fasted dogs were examined during a basal and two 120-min euglycemic periods using arteriovenous balance techniques. Results indicate that the portal signal effectively activates the NHGU under hyperinsulinemic but not hyperglycemic conditions. Nonhepatic glucose uptake was suppressed minimally under euglycemic but not hyperglycemic conditions.

A study was conducted to analyze the time course of the decay of the effect of the portal signal on glucose uptake by the liver and nonhepatic tissues of dogs during the presence of hyperglycemia and hyperinsulinemia. Plasma glucose was assayed with the glucose oxidase technique. Results indicated that the effects of the portal signal on hepatic and peripheral glucose uptake are reversible even under hyperinsulinemic conditions.

A study was conducted to determine if the effects of insulin delivered directly to the liver sinusoid will be influenced by the route of delivery. Two routes are examined, namely via portal vein and hepatic artery. Results revealed that both means of infusion have the same effects Insulin infused through the hepatic artery and the portal vein caused the inhibition of glucose production, which effected a change in the liver glycogenolyisis.

Concomitant intraportal delivery of glucose and gluconeogenic amino acids (GNGAA) leads to reduced rates of net hepatic glucose uptake (NHGU), as against rates exhibited during intraportal delivery of glucose without amino acids or intraportal glucose delivery with peripheral amino acid infusion. These were found in a study of the differential effect of amino acid infusion route on NHGU in dogs. Specifically, the hypothesis that the reduction in NHGU occurring during concomitant intraportal delivery of glucose and GNGAA is specific to the intraportal route of amino acid delivery was tested.

Research was conducted to examine the hypothesis that hepatic glucose uptake (NHGU) rapidly decreases after removal of the portal signal in conscious dogs. The objective of the study was to investigate the decay of the effect of the portal signal on NHGU. A sample of five 42-h-fasted conscious mongrel dogs of either sex were used for the experiment. Results indicate that the portal signal induces a rapid shift of the liver into net glucose uptake.

Research was conducted to quantify net hepatic glucose uptake (NHGU) and hepatic glycogen synthesis during concomitant intraportal infusion of glucose and a mixture of gluconeogenic amino acids and to analyze glycogen synthesis in 42-h-fasted dogs. Results indicate that intraportal gluconeogenic amino acid infusion directed glucose carbon away from the liver. Also, there was equivalent net hepatic carbon uptake whether or not an infusion of amino acid was conducted.

Research was conducted to study the effects of a selective rise in liver sinusoidal norepinephrine on hepatic glucose production (HGP). Doppler flow probes were utilized to estimate total hepatic blood flow while total glucose production was expressed using compartment models. Results indicated that the increase in glucose production caused by the norepinephrine release would lead to an increase in hepatic glycogenolysis.