Combined intraportal infusion of acetylcholine and adrenergic blockers augments net hepatic glucose uptake

The relationships between acetylcholine-induced chest pain, objective measures of coronary vascular function and symptom status

Background

Acetylcholine-induced chest pain is routinely measured during the assessment of microvascular function.

Aims

The aim was to determine the relationships between acetylcholine-induced chest pain and both symptom burden and objective measures of vascular function.

Methods

In patients with angina but no obstructive coronary artery disease, invasive studies determined the presence or absence of chest pain during both acetylcholine and adenosine infusion. Thermodilution-derived coronary blood flow (CBF) and index of microvascular resistance (IMR) was determined at rest and during both acetylcholine and adenosine infusion. Patients with epicardial spasm (>90%) were excluded; vasoconstriction between 20% and 90% was considered endothelial dysfunction.

Results

Eighty-seven patients met the inclusion criteria. Of these 52 patients (60%) experienced chest pain during acetylcholine while 35 (40%) did not. Those with acetylcholine-induced chest pain demonstrated: (1) Increased CBF at rest (1.6 ± 0.7 vs. 1.2 ± 0.4, p = 0.004) (2) Decreased IMR with acetylcholine (acetylcholine-IMR = 29.7 ± 16.3 vs. 40.4 ± 17.1, p = 0.004), (3) Equivalent IMR following adenosine (Adenosine-IMR: 21.1 ± 10.7 vs. 21.8 ± 8.2, p = 0.76), (4) Increased adenosine-induced chest pain (40/52 = 77% vs. 7/35 = 20%, p < 0.0001), (5) Increased chest pain during exercise testing (30/46 = 63% vs. 4/29 = 12%, p < 0.00001) with no differences in exercise duration or electrocardiographic changes, and (6) Increased prevalence of epicardial endothelial dysfunction (33/52 = 63% vs. 14/35 = 40%, p = 0.03).

Conclusions

After excluding epicardial spasm, acetylcholine-induced chest pain is associated with increased pain during exercise and adenosine infusion, increased coronary blood flow at rest, decreased microvascular resistance in response to acetylcholine and increased prevalence of epicardial endothelial dysfunction. These findings raise questions about the mechanisms underlying acetylcholine-induced chest pain.

Lipid rafts of mouse liver contain nonextended and extended acetylcholinesterase variants along with M3 muscarinic receptors

The observation of acetylcholinesterase (AChE) type H (AChE_H), which is the predominant AChE variant in visceral organs and immune cells, in lipid rafts of muscle supports functional reasons for the raft targeting of glypiated AChE_H The search for these reasons revealed that liver AChE activity is mostly confined to rafts and that the liver is able to make N-extended AChE variants and target them to rafts. These results prompted us to test whether AChE and muscarinic receptors existed in the same raft. Isolation of flotillin-2-rich raft fractions by their buoyancy in sucrose gradients, followed by immunoadsorption and matrix-assisted laser desorption ionization-time of flight-mass spectrometry application, gave the following results: 1) most hepatic AChE activity emanates from AChE-H mRNA, and its product, glypiated AChE_H, accumulates in rafts; 2) N-extended N-AChE readthrough variant, nonglypiated N-AChE_H, and N-AChE tailed variant were all identified in liver rafts; and 3) M3 AChRs were observed in rafts, and coprecipitation of raft-confined N-AChE and M3 receptors by using anti-M3 antibodies showed that enzyme and receptor reside in the same raft unit. A raft domain that harbors tightly packed muscarinic receptor and AChE may represent a molecular device that, by means of which, the intensity and duration of cholinergic inputs are regulated.-Montenegro, M. F., Cabezas-Herrera, J., Campoy, F. J., Muñoz-Delgado, E., Vidal, C. J. Lipid rafts of mouse liver contain nonextended and extended acetylcholinesterase variants along with M3 muscarinic receptors.

Acetylcholine promotes Ca2+ and NO-oscillations in adipocytes implicating Ca2+→NO→cGMP→cADP-ribose→Ca2+ positive feedback loop--modulatory effects of norepinephrine and atrial natriuretic peptide

PURPOSE

This study investigated possible mechanisms of autoregulation of Ca(2+) signalling pathways in adipocytes responsible for Ca(2+) and NO oscillations and switching phenomena promoted by acetylcholine (ACh), norepinephrine (NE) and atrial natriuretic peptide (ANP).

METHODS

Fluorescent microscopy was used to detect changes in Ca(2+) and NO in cultures of rodent white adipocytes. Agonists and inhibitors were applied to characterize the involvement of various enzymes and Ca(2+)-channels in Ca(2+) signalling pathways.

RESULTS

ACh activating M3-muscarinic receptors and Gβγ protein dependent phosphatidylinositol 3 kinase induces Ca(2+) and NO oscillations in adipocytes. At low concentrations of ACh which are insufficient to induce oscillations, NE or α1, α2-adrenergic agonists act by amplifying the effect of ACh to promote Ca(2+) oscillations or switching phenomena. SNAP, 8-Br-cAMP, NAD and ANP may also produce similar set of dynamic regimes. These regimes arise from activation of the ryanodine receptor (RyR) with the implication of a long positive feedback loop (PFL): Ca(2+)→NO→cGMP→cADPR→Ca(2+), which determines periodic or steady operation of a short PFL based on Ca(2+)-induced Ca(2+) release via RyR by generating cADPR, a coagonist of Ca(2+) at the RyR. Interplay between these two loops may be responsible for the observed effects. Several other PFLs, based on activation of endothelial nitric oxide synthase or of protein kinase B by Ca(2+)-dependent kinases, may reinforce functioning of main PFL and enhance reliability. All observed regimes are independent of operation of the phospholipase C/Ca(2+)-signalling axis, which may be switched off due to negative feedback arising from phosphorylation of the inositol-3-phosphate receptor by protein kinase G.

CONCLUSIONS

This study presents a kinetic model of Ca(2+)-signalling system operating in adipocytes and integrating signals from various agonists, which describes it as multivariable multi feedback network with a family of nested positive feedback.

A cyclic guanosine monophosphate-dependent pathway can regulate net hepatic glucose uptake in vivo

We previously showed that hepatic nitric oxide regulates net hepatic glucose uptake (NHGU), an effect that can be eliminated by inhibiting hepatic soluble guanylate cyclase (sGC), suggesting that the sGC pathway is involved in the regulation of NHGU. The aim of the current study was to determine whether hepatic cyclic guanosine monophosphate (cGMP) reduces NHGU. Studies were performed on conscious dogs with transhepatic catheters. A hyperglycemic-hyperinsulinemic clamp was established in the presence of portal vein glucose infusion. 8-Br-cGMP (50 µg/kg/min) was delivered intraportally, and either the glucose load to the liver (CGMP/GLC; n = 5) or the glucose concentration entering the liver (CGMP/GCC; n = 5) was clamped at 2× basal. In the control group, saline was given intraportally (SAL; n = 10), and the hepatic glucose concentration and load were doubled. 8-Br-cGMP increased portal blood flow, necessitating the two approaches to glucose clamping in the cGMP groups. NHGU (mg/kg/min) was 5.8 ± 0.5, 2.7 ± 0.5, and 4.8 ± 0.3, whereas the fractional extraction of glucose was 11.0 ± 1, 5.5 ± 1, and 8.5 ± 1% during the last hour of the study in SAL, CGMP/GLC, and CGMP/GCC, respectively. The reduction of NHGU in response to 8-Br-cGMP was associated with increased AMP-activated protein kinase phosphorylation. These data indicate that changes in liver cGMP can regulate NHGU under postprandial conditions.

Atypical antipsychotics and the neural regulation of food intake and peripheral metabolism

The atypical antipsychotics (AAPs) are associated with weight gain and an increased incidence of metabolic disease including type 2 diabetes mellitus. Epidemiological, cross-sectional and prospective studies suggest that two of the AAPs, olanzapine and clozapine, cause the most dramatic weight gain and metabolic impairments including increased fasting glucose, insulin and triglycerides. Relative to the other AAPs, both olanzapine and clozapine exhibit a particularly high antagonistic affinity for histamine and muscarinic receptors which have been hypothesized as mediators of the reported increase in weight and glucose abnormalities. In this article, we review the current evidence for the AAP associated weight gain and abnormal glucose metabolism. We postulate that the effects of the AAPs on food intake and peripheral metabolism are initially independently regulated but with increasing body adiposity, the early AAP-induced impairments in peripheral metabolism will be exacerbated, thereby establishing a vicious cycle such that the effects of the AAP are magnified by the known pathophysiological consequences of obesity. Furthermore, we examine how inhibition of the histaminergic pathway may mediate increases in food intake and the potential role of the vagus nerve in the reported peripheral metabolic effects.

The role of the autonomic nervous liver innervation in the control of energy metabolism

Despite a longstanding research interest ever since the early work by Claude Bernard, the functional significance of autonomic liver innervation, either sympathetic or parasympathetic, is still ill defined. This scarcity of information not only holds for the brain control of hepatic metabolism, but also for the metabolic sensing function of the liver and the way in which this metabolic information from the liver affects the brain. Clinical information from the bedside suggests that successful human liver transplantation (implying a complete autonomic liver denervation) causes no life threatening metabolic derangements, at least in the absence of severe metabolic challenges such as hypoglycemia. However, from the benchside, data are accumulating that interference with the neuronal brain-liver connection does cause pronounced changes in liver metabolism. This review provides an extensive overview on how metabolic information is sensed by the liver, and how this information is processed via neuronal pathways to the brain. With this information the brain controls liver metabolism and that of other organs and tissues. We will pay special attention to the hypothalamic pathways involved in these liver-brain-liver circuits. At this stage, we still do not know the final destination and processing of the metabolic information that is transferred from the liver to the brain. On the other hand, in recent years, there has been a considerable increase in the understanding which brain areas are involved in the control of liver metabolism via its autonomic innervation. However, in view of the ever rising prevalence of type 2 diabetes, this potentially highly relevant knowledge is still by far too limited. Thus the autonomic innervation of the liver and its role in the control of metabolism needs our continued and devoted attention.

Hepatic muscarinic acetylcholine receptors are not critically involved in maintaining glucose homeostasis in mice

OBJECTIVE

An increase in the rate of hepatic glucose production is the major determinant of fasting hyperglycemia in type 2 diabetes. A better understanding of the signaling pathways and molecules that regulate hepatic glucose metabolism is therefore of great clinical importance. Recent studies suggest that an increase in vagal outflow to the liver leads to decreased hepatic glucose production and reduced blood glucose levels. Since acetylcholine (ACh) is the major neurotransmitter of the vagus nerve and exerts its parasympathetic actions via activation of muscarinic ACh receptors (mAChRs), we examined the potential metabolic relevance of hepatocyte mAChRs.

RESEARCH DESIGN AND METHODS

We initially demonstrated that the M(3) mAChR is the only mAChR subtype expressed by mouse liver/hepatocytes. To assess the physiological role of this receptor subtype in regulating hepatic glucose fluxes and glucose homeostasis in vivo, we used gene targeting and transgenic techniques to generate mutant mice lacking or overexpressing M(3) receptors in hepatocytes only.

RESULTS

Strikingly, detailed in vivo phenotyping studies failed to reveal any significant metabolic differences between the M(3) receptor mutant mice and their control littermates, independent of whether the mice were fed regular or a high-fat diet. Moreover, the expression levels of genes for various key transcription factors, signaling molecules, and enzymes regulating hepatic glucose fluxes were not significantly altered in the M(3) receptor mutant mice.

CONCLUSIONS

This rather surprising finding suggests that the pronounced metabolic effects mediated by activation of hepatic vagal nerves are mediated by noncholinergic signaling pathways.

Hepatic portal venous delivery of a nitric oxide synthase inhibitor enhances net hepatic glucose uptake

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(G)-nitro-L-arginine methyl ester (L-NAME), a nonspecific NOS inhibitor; n = 11] intraportally at 0.3 mg x kg(-1) x min(-1) for 90 min (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 mug x kg(-1) x min(-1) while six received saline (LN/SIN-1 and LN/SAL, respectively). Net hepatic fractional glucose extraction (NHFE) in control dogs was 0.034 +/- 0.016, 0.039 +/- 0.015, and 0.056 +/- 0.019 during P1, P2, and P3, respectively. NHFE in LN was 0.045 +/- 0.009 and 0.111 +/- 0.007 during P1 and P2, respectively (P < 0.05 vs. control during P2), and 0.087 +/- 0.009 and 0.122 +/- 0.016 (P < 0.05) during P3 in LN/SIN-1 and LN/SAL, respectively. During P2, arterial glucose was 204 +/- 5 vs. 138 +/- 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 +/- 0.008, 0.093 +/- 0.023, and 0.122 +/- 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 NHFE, an effect partially reversed by SIN-1.

The effect of vagal cooling on canine hepatic glucose metabolism in the presence of hyperglycemia of peripheral origin

We examined the role of vagus nerves in the transmission of the portal glucose signal in conscious dogs. At time 0, somatostatin infusion was started along with intraportal insulin and glucagon at 4-fold basal and basal rates, respectively. Glucose was infused via a peripheral vein to create hyperglycemia ( approximately 2 fold basal). At t = 90, hollow coils around the vagus nerves were perfused with -10 degrees C or 37 degrees C solution in the vagally cooled (COOL) and sham-cooled (SHAM) groups, respectively (n = 6 per group). Effectiveness of vagal blockade was demonstrated by increase in heart rate during perfusion in the COOL vs SHAM groups (183 +/- 3 vs 102 +/- 5 beats per minute, respectively) and by prolapse of the third eyelid in the COOL group. Arterial plasma insulin (22 +/- 2 and 24 +/- 3 micro U/mL) and glucagon (37 +/- 5 and 40 +/- 4 pg/mL) concentrations did not change significantly between the first experimental period and the coil perfusion period in either the SHAM or COOL group, respectively. The hepatic glucose load throughout the entire experiment was 46 +/- 1 and 50 +/- 2 mg . kg(-1) . min(-1) in the SHAM and COOL groups, respectively. Net hepatic glucose uptake (NHGU) did not differ in the SHAM and COOL groups before (2.2 +/- 0.5 and 2.9 +/- 0.8 mg . kg(-1) . min(-1), respectively) or during the cooling period (3.0 +/- 0.5 and 3.4 +/- 0.6 mg . kg(-1) . min(-1), respectively). Likewise, net hepatic glucose fractional extraction and nonhepatic glucose uptake and clearance were not different between groups during coil perfusion. Interruption of vagal signaling in the presence of hyperinsulinemia and hyperglycemia resulting from peripheral glucose infusion did not affect NHGU, further supporting our previous suggestion that vagal input to the liver is not a primary determinant of NHGU.

Role of the hepatic sympathetic nerves in the regulation of net hepatic glucose uptake and the mediation of the portal glucose signal

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.kg(-1).min(-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.kg(-1).min(-1)) in CON and DEN were 55+/-3 and 54+/-4 in the peripheral periods and 55+/-3 and 55+/-4 in P2, respectively. The arterial insulin and glucagon levels remained basal in both groups. NHGU (mg.kg(-1).min(-1)) in CON averaged 1.7+/-0.3 during PE and increased to 2.9+/-0.3 during P2. NHGU (mg.kg(-1).min(-1)) was greater in DEN than CON (P<0.05) during PE (2.9+/-0.4) and failed to increase significantly (3.2+/-0.2) during P2 (not significant vs. CON). Selective sympathetic denervation increased NHGU during hyperglycemia but significantly blunted the response to portal glucose delivery.

Vagal cooling and concomitant portal norepinephrine infusion do not reduce net hepatic glucose uptake in conscious dogs

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(-1).min(-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(-1).min(-1) during P2. The effectiveness of vagal suppression was demonstrated by the increase in heart rate during P2 (111 +/- 17, 167 +/- 16, and 105 +/- 13 beats/min in group 1 and 71 +/- 6, 200 +/- 11, and 76 +/- 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 +/- 0.4, 4.1 +/- 0.6, and 4.0 +/- 1.2 mg.kg(-1).min(-1) in group 1 and 5.0 +/- 0.9, 5.6 +/- 0.7, and 6.1 +/- 0.9 mg.kg(-1).min(-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.

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

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 approximately 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 microU/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.

Effect of intraportal glucagon-like peptide-1 on glucose metabolism in conscious dogs

Arteriovenous difference and tracer ([3-(3)H]glucose) techniques were used in 42-h-fasted conscious dogs to identify any insulin-like effects of intraportally administered glucagon-like 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(-1). min(-1) in eight dogs, at 10 and 20 pmol. kg(-1). min(-1) in seven dogs, and at 0 pmol. kg(-1). min(-1) in eight dogs (control group). Net hepatic glucose uptake was significantly enhanced during GLP-1 infusion at 20 pmol. kg(-1). min(-1) [21.8 vs. 13.4 micromol. kg(-1). min(-1) (control), P < 0.05]. Glucose utilization was significantly increased during infusion at 10 and 20 pmol. kg(-1). min(-1) [87.3 +/- 8.3 and 105.3 +/- 12.8, respectively, vs. 62.2 +/- 5.3 and 74.7 +/- 7.4 micromol. kg(-1). min(-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(-1). min(-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(-1). min(-1) (25 and 46% greater than control) and tended (P = 0.1) to increase during GLP-1 infusion at 20 pmol. kg(-1). min(-1) (24% greater than control). Intraportal infusion of GLP-1 at high physiological and pharmacological rates increased glucose disposal primarily in nonhepatic tissues.

Acetylcholine affects rat liver metabolism via type 3 muscarinic receptors in hepatocytes

Although the role of acetylcholine (Ach) in hepatic glucose metabolism is well elucidated, it is still unclear if it influences gluconeogenesis, glycogenolysis and high-energy phosphate metabolism, and if it does what the mechanisms of this influence are. Therefore, using isolated perfused rat liver as a model, we have studied the effect of Ach on oxygen consumption, synthesis of glucose from lactate and pyruvate, glycogen formation, mitochondrial oxidative phosphorylation and ATP-synthesis. We have established that effects of Ach on oxygen consumption depend on its concentration. When used at a concentration of 10(-7) M, Ach exerts maximum stimulatory effect, while its infusion at 10(-6) M causes a decrease of oxygen consumption by the liver. Moreover, when used at a concentration of 10(-6) M or 10(-7) M, Ach increases rates of glucose production from the gluconeogenic substrates lactate and pyruvate, leading to enhanced glycogen content in perfused liver. It was also shown that Ach possesses a stimulating effect on alanine and aspartate aminotransferases. As detected by 31P NMR spectroscopy, continuous liver perfusion with pyruvate and lactate in the presence of Ach leads to a significant decrease of ATP level, implying enhanced energy requirements for gluconeogenesis under these conditions. Elimination of the described effects of Ach by atropine, the antagonist of muscarinic receptors, and identification of the type 3 muscarinic receptors (m3) in isolated hepatocytes as well as in whole liver, imply that Ach may exert its effect on liver metabolism through m3 receptors.

Free fatty acid-induced peripheral insulin resistance augments splanchnic glucose uptake in healthy humans

To investigate the effect of elevated plasma free fatty acid (FFA) concentrations on splanchnic glucose uptake (SGU), we measured SGU in nine healthy subjects (age, 44 +/- 4 yr; body mass index, 27.4 +/- 1.2 kg/m(2); fasting plasma glucose, 5.2 +/- 0.1 mmol/l) during an Intralipid-heparin (LIP) infusion and during a saline (Sal) infusion. SGU was estimated by the oral glucose load (OGL)-insulin clamp method: subjects received a 7-h euglycemic insulin (100 mU x m(-2) x min(-1)) clamp, and a 75-g OGL was ingested 3 h after the insulin clamp was started. After glucose ingestion, the steady-state glucose infusion rate (GIR) during the insulin clamp was decreased to maintain euglycemia. SGU was calculated by subtracting the integrated decrease in GIR during the period after glucose ingestion from the ingested glucose load. [3-(3)H]glucose was infused during the initial 3 h of the insulin clamp to determine rates of endogenous glucose production (EGP) and glucose disappearance (R(d)). During the 3-h euglycemic insulin clamp before glucose ingestion, R(d) was decreased (8.8 +/- 0.5 vs. 7.6 +/- 0.5 mg x kg(-1) x min(-1), P < 0.01), and suppression of EGP was impaired (0.2 +/- 0.04 vs. 0.07 +/- 0.03 mg x kg(-1) x min(-1), P < 0.01). During the 4-h period after glucose ingestion, SGU was significantly increased during the LIP vs. Sal infusion study (30 +/- 2 vs. 20 +/- 2%, P < 0.005). In conclusion, an elevation in plasma FFA concentration impairs whole body glucose R(d) and insulin-mediated suppression of EGP in healthy subjects but augments SGU.