Renal Glucose Production Research Articles

Effect of Dapagliflozin on Renal and Hepatic Glucose Kinetics in T2D and NGT Subjects.

Acute and chronic SGLT-2 inhibition increase endogenous glucose production (EGP). However, the organ - liver versus kidney - responsible for the increase in EGP has not been identified. 20 T2DM and 12 NGT subjects received [3-3H]-glucose infusion (to measure total EGP) in combination with arterial and renal vein catheterization and PAH infusion for determination of renal blood flow. Total EGP, net renal arteriovenous balance, and renal glucose production were measured before and 4 hours after dapagliflozin and placebo administration. Following DAPA, EGP increased in both T2D and NGT from baseline to 240 minutes, while there was a significant time-related decrease after placebo in T2D. Renal glucose production at baseline was <5% of basal EGP in both groups and did not change significantly following DAPA in either NGT and T2D. Renal glucose uptake (sum of tissue glucose uptake plus glucosuria) increased in both T2D and NGT following DAPA (P<0.05 vs placebo). The increase in RGU was entirely explained by the increase in glucosuria. Single dose of dapagliflozin significantly increased EGP, which primarily is explained by an increase in hepatic glucose production, establishing the existence of a novel renal-hepatic axis.

Metabolic Fluxes in the Renal Cortex Are Dysregulated InVivo in Response to High-Fat Diet.

Diabetes and obesity are risk factors for kidney disease. While renal glucose production increases in diabetes, recent data suggest that gluconeogenic and oxidative capacity decline in kidney disease. Thus, metabolic dysregulation caused by diet-induced insulin resistance may sensitize the kidney for a loss in function. Here we examined how diet-induced insulin resistance disrupts mitochondrial metabolic fluxes in the renal cortex in vivo. C57Bl/6J mice were rendered insulin resistant through high-fat (HF) feeding; anaplerotic, cataplerotic, and oxidative metabolic fluxes in the cortex were quantified through 13C-isotope tracing during a hyperinsulinemic-euglycemic clamp. As expected, HF-fed mice exhibited increased body weight, gluconeogenesis, and systemic insulin resistance compared to chow-fed mice. Relative to the citric acid cycle, HF-feeding increased metabolic flux through pyruvate carboxylation (anaplerosis) and phosphoenolpyruvate carboxykinase (cataplerosis) while decreasing flux through the pyruvate dehydrogenase complex in the cortex. Furthermore, the relative flux from non-pyruvate sources of acetyl-CoA profoundly increased in the cortex of HF-fed mice, correlating with a marker of oxidative stress. The data demonstrate that HF-feeding spares pyruvate from dehydrogenation at the expense of increasing cataplerosis, which may underpin renal gluconeogenesis during insulin resistance; the results also support the hypothesis that dysregulated oxidative metabolism in the kidney contributes to metabolic disease.

THU123 Knockout Of Renal Glut2 Gene Activates The Hypothalamic-pituitary-adrenal Axis To Increase Glucose Production In Mice

Abstract Disclosure: T.S. Faniyan: None. J. Robles: None. X. Zhang: None. S. Bathina: None. P.S. Brookes: None. R.J. Perry: None. K.H. Chhabra: None. We recently reported the contribution of renal GLUT2 (glucose transporter 2) to systemic glucose homeostasis using a mouse model in which we can knockout renal Glut2 gene at a desired time. Renal Glut2 knockout mice have improved glucose tolerance and are protected from high-fat diet or streptozocin-induced diabetes because they excrete excess blood glucose in urine. Interestingly, despite the profound loss of glucose in urine, renal Glut2 knockout mice have normal fasting blood glucose levels. These findings indicate that an increase in endogenous glucose production may be compensating for the loss of glucose in urine. To determine the mechanisms responsible for evoking the increase in endogenous glucose production, we focused on studying the hypothalamic-pituitary-adrenal (HPA) axis because of its established role in elevating blood glucose levels. We used ELISA to measure circulating adrenocorticotrophic hormone (ACTH) and corticosterone, which are major hormones of the HPA axis. Moreover, we used fluorescence in situ hybridization to assess the expression of hypothalamic corticotropin releasing hormone gene (Crh). We also performed in vitro metabolomics analysis of the mouse liver using mass spectrometry. Finally, we measured glucose production from pyruvate in vivo in the liver and kidney using mass isotopomer distribution analysis. Renal Glut2 knockout mice had increased (p&amp;lt;0.05) levels of hypothalamic Crh (100 ±13 vs 142 ±9 %, control vs experimental), circulating ACTH (120 ±8 vs 213 ±12 pg/ml), and corticosterone (30.4 ±5.5 vs 115 ±15.2 ng/ml). In addition, we found that metabolites such as hepatic glucose-6-phosphate (19.2 ±1.5 vs 15 ±1 arbitrary unit, control vs experimental), glucose-1-phosphate (20 ±1.5 vs 15.5 ±1), and fructose-6-phosphate (16 ±1.2 vs 12.4 ±0.8) were decreased in renal Glut2 knockout mice. We further observed that glucose production was increased in both the liver (15.1 ±0.4 vs 18.4 ±0.5 mg/kg/min) and kidney (1.7 ±0.2 vs 2.6 ±0.3 mg/kg/min) in renal Glut2 knockout mice. Our results demonstrate that loss of renal Glut2 causes hyperactivation of the HPA axis coupled with decrease in hepatic glucose metabolism and increase in hepatic as well as renal glucose production. These findings may explain how the renal Glut2 knockout mice prevent hypoglycemia despite massive glycosuria. Altogether, our study identifies a novel crosstalk between the kidneys, hypothalamus, and adrenal glands to regulate systemic glucose homeostasis. This information may be useful in either optimizing the efficacy of drugs that enhance glycosuria to treat diabetes or addressing the side effects of such drugs on the HPA axis. Presentation: Thursday, June 15, 2023

Dental rehabilitation in a young patient with glycogen storage disease type 1B

A young woman, known to have glycogen storage disease type 1B (GSD1B) presents with severe periodontitis. GDS1B causes decreased hepatic and renal glucose production and in many cases neutropenia and neutrophil dysfunction leading to recurrent infections. It was decided to treat the patient by extraction of the most affected teeth and retention of the remaining teeth through periodontal treatment, both with antibiotic prophylaxis. After a follow-up period of 1.5 years, during which there was no visible improvement, it was decided to do a full dental extraction and fabricate complete dentures. Due to subsequent bone resorption in both jaws, the dentures were not functional. After consulting the internist and the oral and maxillofacial surgeon, the decision was then made to place dental implants in both the upper and lower jaw for implant-supported prosthetics. After successful treatment and an osseointegration period, the prosthetics were placed. 1 year after placement, there is a stable implantological situation, without pockets or apparent bone loss. The start of SGLT2 medication may have played a significant role in this.

55-LB: Effect of Dapagliflozin on Renal and Hepatic Glucose Kinetics in T2DM and NGT Subjects

We previously have shown that both acute and chronic SGLT-2 inhibition increases endogenous glucose production (EGP) . However, the organ - liver versus kidney - responsible for the increase in EGP has not been identified. We assessed the effect of a single dose of Dapagliflozin or Placebo on renal glucose production in 13 T2DM (age=57.5±1.8 yrs, BMI = 30±1.4 kg/m2) and 9 NGT (age 42±2 3 yrs, BMI = 30±1.1 kg/m2) subjects. Renal glucose production was measured using arteriovenous balance technique across the kidney combined with [3-3H] glucose infusion and PAH infusion (for determination of renal blood flow) before and 4 hours after administration of Dapagliflozin (10 mg) and Placebo; thus, each subject served as their own control. EGP increased following DAPA in both T2DM (2.00±0.11 to 2.43±0.15, P&amp;lt;0.05) and NGT (1.72±0.11 to 2.1±0.16, p&amp;lt;0.05) , while it decreased after placebo in T2DM (2.02±0.12 vs. 1.15±0.06) and NGT (2.10±0.2 vs. 2.05±0.1) (both p&amp;lt;0.01, DAPA vs. placebo) . The fractional renal extraction of glucose (0.02± 0.004 vs. 2.99 ± 1.0, p=0.001 in T2DM, and 0.02± 0.004 vs. 1.62± 1.4 in NGT, p=NS) and renal glucose uptake (0.067 ± 0.02 vs. 0.347 ± 0.06 in T2DM and 0.08 ± 0.02 vs. 0.27 ± 0.08 mg/kg.min in NGT) were higher following DAPA vs. placebo (p&amp;lt;0.05) and were entirely explained by the increase in glucosuria. There was a small, non-significant increase (0.065 &amp; 0.032 mg/kg.min, respectively) in renal glucose production (RGP) following dapagliflozin in T2DM and NGT compared to the 0.45 mg/kg.min increase in total body EGP. Conclusion: A single dose of Dapagliflozin significantly increases EGP which primarily is explained by an increase in hepatic glucose production. Disclosure X. Chen: None. C. Solis-herrera: Speaker’s Bureau; Novo Nordisk. D. Tripathy: None. A. A. Hansis-diarte: None. R. Chilton: Advisory Panel; AstraZeneca, Boehringer Ingelheim International GmbH, Nova Biomedical. E. Cersosimo: Research Support; AstraZeneca. R. A. Defronzo: Advisory Panel; AstraZeneca, Boehringer Ingelheim International GmbH, Intarcia Therapeutics, Inc., Novo Nordisk, Research Support; AstraZeneca, Boehringer Ingelheim International GmbH, Merck &amp; Co., Inc., Speaker’s Bureau; AstraZeneca. Funding Astra Zeneca

Decreased Renal Gluconeogenesis Is a Hallmark of Chronic Kidney Disease.

CKD is associated with alterations of tubular function. Renal gluconeogenesis is responsible for 40% of systemic gluconeogenesis during fasting, but how and why CKD affects this process and the repercussions of such regulation are unknown. We used data on the renal gluconeogenic pathway from more than 200 renal biopsies performed on CKD patients and from 43 kidney allograft patients, and studied three mouse models, of proteinuric CKD (POD-ATTAC), of ischemic CKD, and of unilateral urinary tract obstruction. We analyzed a cohort of patients who benefitted from renal catheterization and a retrospective cohort of patients hospitalized in the intensive care unit. Renal biopsies of CKD and kidney allograft patients revealed a stage-dependent decrease in the renal gluconeogenic pathway. Two animal models of CKD and one model of kidney fibrosis confirm gluconeogenic downregulation in injured proximal tubule cells. This shift resulted in an alteration of renal glucose production and lactate clearance during an exogenous lactate load. The isolated perfused kidney technique in animal models and renal venous catheterization in CKD patients confirmed decreased renal glucose production and lactate clearance. In CKD patients hospitalized in the intensive care unit, systemic alterations of glucose and lactate levels were more prevalent and associated with increased mortality and a worse renal prognosis at follow-up. Decreased expression of the gluconeogenesis pathway and its regulators predicted faster histologic progression of kidney disease in kidney allograft biopsies. Renal gluconeogenic function is impaired in CKD. Altered renal gluconeogenesis leads to systemic metabolic changes with a decrease in glucose and increase in lactate level, and is associated with a worse renal prognosis.

Multitissue 2H/13C flux analysis reveals reciprocal upregulation of renal gluconeogenesis in hepatic PEPCK-C-knockout mice.

The liver is the major source of glucose production during fasting under normal physiological conditions. However, the kidney may also contribute to maintaining glucose homeostasis in certain circumstances. To test the ability of the kidney to compensate for impaired hepatic glucose production in vivo, we developed a stable isotope approach to simultaneously quantify gluconeogenic and oxidative metabolic fluxes in the liver and kidney. Hepatic gluconeogenesis from phosphoenolpyruvate was disrupted via liver-specific knockout of cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C; KO). 2H/13C isotopes were infused in fasted KO and WT littermate mice, and fluxes were estimated from isotopic measurements of tissue and plasma metabolites using a multicompartment metabolic model. Hepatic gluconeogenesis and glucose production were reduced in KO mice, yet whole-body glucose production and arterial glucose were unaffected. Glucose homeostasis was maintained by a compensatory rise in renal glucose production and gluconeogenesis. Renal oxidative metabolic fluxes of KO mice increased to sustain the energetic and metabolic demands of elevated gluconeogenesis. These results show the reciprocity of the liver and kidney in maintaining glucose homeostasis by coordinated regulation of gluconeogenic flux through PEPCK-C. Combining stable isotopes with mathematical modeling provides a versatile platform to assess multitissue metabolism in various genetic, pathophysiological, physiological, and pharmacological settings.

207-LB: Simultaneous 2H/13C Assessment of Liver and Kidney Metabolic Fluxes Reveals Reciprocal Upregulation of Renal Gluconeogenesis in Hepatic PEPCK-C Knockout Mice

The liver is the major source of glucose production during fasting under normal physiological conditions. However, the kidney may also contribute to maintaining glucose homeostasis in certain circumstances. To test the ability of the kidney to compensate for impaired hepatic glucose production in vivo, we developed a novel stable isotope approach to simultaneously quantify hepatic and renal gluconeogenic and oxidative metabolic fluxes. Hepatic gluconeogenesis from phosphoenolpyruvate was disrupted via liver-specific knockout of cytosolic PEPCK (KO). Experiments were performed in fasted (~18hr) KO and wild-type (WT) littermate mice (n≥4, per group) fitted with jugular vein and carotid artery catheters. A multi-compartment metabolic model was used to assess fluxes using the isotopic enrichment of plasma and tissue metabolites from mice infused with 2H/13C isotopes. Hepatic gluconeogenesis and glucose production were reduced in KO mice, yet whole-body glucose production and arterial glucose were unaffected. Glucose homeostasis was maintained by a compensatory rise in renal glucose production and gluconeogenesis of 17 and 30-fold, respectively. This was consistent with a ~2-fold rise in PEPCK-C and mitochondrial PEPCK protein expression in the kidneys. Renal oxidative metabolic fluxes of KO mice increased to sustain the energetic and metabolic demands of elevated gluconeogenesis. These results show the reciprocity of the liver and kidney in maintaining glucose homeostasis by regulating gluconeogenic flux through PEPCK-C. This reciprocity creates a layer of redundancy that protects glucose homeostasis in the event that hepatic glucose production is impaired. Combining stable isotopes with mathematical modeling provides a versatile platform to assess multi-tissue metabolism in various genetic, (patho)physiological, and pharmacological settings. Disclosure M. Rahim: None. C. M. Hasenour: Employee; Self; Eli Lilly and Company. T. Bednarski: None. C. C. Hughey: None. D. Wasserman: None. J. Young: Consultant; Self; Pfizer Inc., Stock/Shareholder; Self; Metalytics. Funding National Institutes of Health (R01DK106348, U01CA235508, T32DK101003, U24DK059637)

Sodium-glucose co-transporter 2 inhibitors: mechanisms of renal action. Implications for diabetes and heart failure

The liver is not the exclusive site of glucose production in humans in the post-absorption state. Experimental data showed that the kidney is able of carrying out gluconeogenesis. Renal glucose production accounts for 20% of systemic glucose production. Evidence indicates that the kidney is able to reabsorb glucose from the glomerular filtrate through the sodium-glucose co-transporters (SGLT) 1 and 2 placed under the Bowman's capsule, in the thick portion of the proximal convoluted tubule, preserving this essential energy substrate for the organism. The maximal renal glucose reabsorption capacity (TmG), as well as the threshold for the spillover of glucose in the urine, are higher in diabetics than normal subjects and contribute to the hyperglycemic state in the absence of glycosuria. The administration of SGLT2 inhibitors in diabetics improves the excretion of sodium and glucose, reducing the threshold of glycosuria and TmG. This also restores the sodium concentration in the filtrate that reaches the macula densa (juxtaglomerular apparatus), which signals the appropriate perfusion of the kidney, defusing the secretion of renin and the activation of the neurohormonal axis that leads to the production of angiotensin II.Large clinical trials conducted with SGLT2 inhibitors in subjects with type 2 diabetes mellitus have demonstrated the great ability of this new class of drugs to achieve cardiac and renal benefits. All studies have shown SGLT2 inhibitors reduce the risk of hospitalizations for heart failure and the progression of kidney damage. A part of the favorable mechanisms is mediated by the natriuretic effect that is associated with the glycosuric effect, which reduces the activation of the renin-angiotensin-aldosterone system together with glomerular hyperfiltration.The aim of this review is to expand the knowledge among general cardiologists on the role of SGLT2 and SGLT1 in renal glucose homeostasis in healthy and diabetic subjects in the light of a potent class of drugs counteracting heart failure.

Glucose Metabolism in the Kidney: Neurohormonal Activation and Heart Failure Development.

The liver is not the exclusive site of glucose production in humans in the postabsorptive state. Robust data support that the kidney is capable of gluconeogenesis and studies have demonstrated that renal glucose production can increase systemic glucose production. The kidney has a role in maintaining glucose body balance, not only as an organ for gluconeogenesis but by using glucose as a metabolic substrate. The kidneys reabsorb filtered glucose through the sodium‐glucose cotransporters sodium‐glucose cotransporter (SGLT) 1 and SGLT2, which are localized on the brush border membrane of the early proximal tubule with immune detection of their expression in the tubularized Bowman capsule. In patients with diabetes mellitus, the renal maximum glucose reabsorptive capacity, and the threshold for glucose passage into the urine, are higher and contribute to the hyperglycemic state. The administration of SGLT2 inhibitors to patients with diabetes mellitus enhances sodium and glucose excretion, leading to a reduction of the glycosuria threshold and tubular maximal transport of glucose. The net effects of SGLT2 inhibition are to drive a reduction in plasma glucose levels, improving insulin secretion and sensitivity. The benefit of SGLT2 inhibitors goes beyond glycemic control, since inhibition of renal glucose reabsorption affects blood pressure and improves the hemodynamic profile and the tubule glomerular feedback. This action acts to rebalance the dense macula response by restoring adenosine production and restraining renin‐angiotensin‐aldosterone activation. By improving renal and cardiovascular function, we explain the impressive reduction in adverse outcomes associated with heart failure supporting the current clinical perspective.

Insulin enhances renal glucose excretion: relation to insulin sensitivity and sodium-glucose cotransport

IntroductionInsulin regulates renal glucose production and utilization; both these fluxes are increased in type 2 diabetes (T2D). Whether insulin also controls urinary glucose excretion is not known.MethodsWe applied the pancreatic...

The role of kidney in the inter-organ coordination of endogenous glucose production during fasting

ObjectiveThe respective contributions to endogenous glucose production (EGP) of the liver, kidney and intestine vary during fasting. We previously reported that the deficiency in either hepatic or intestinal gluconeogenesis modulates the repartition of EGP via glucagon secretion (humoral factor) and gut–brain–liver axis (neural factor), respectively. Considering renal gluconeogenesis reportedly accounted for approximately 50% of EGP during fasting, we examined whether a reduction in renal gluconeogenesis could promote alterations in the repartition of EGP in this situation. MethodsWe studied mice whose glucose-6-phosphatase (G6Pase) catalytic subunit (G6PC) is specifically knocked down in the kidneys (K-G6pc-/- mice) during fasting. We also examined the additional effects of intestinal G6pc deletion, renal denervation and vitamin D administration on the altered glucose metabolism in K-G6pc-/- mice. ResultsCompared with WT mice, K-G6pc-/- mice exhibited (1) lower glycemia, (2) enhanced intestinal but not hepatic G6Pase activity, (3) enhanced hepatic glucokinase (GK encoded by Gck) activity, (4) increased hepatic glucose-6-phosphate and (5) hepatic glycogen spared from exhaustion during fasting. Increased hepatic Gck expression in the post-absorptive state could be dependent on the enhancement of insulin signal (AKT phosphorylation) in K-G6pc-/- mice. In contrast, the increase in hepatic GK activity was not observed in mice with both kidney- and intestine-knockout (KI-G6pc-/- mice). Hepatic Gck gene expression and hepatic AKT phosphorylation were reduced in KI-G6pc-/- mice. Renal denervation by capsaicin did not induce any effect on glucose metabolism in K-G6pc-/- mice. Plasma level of 1,25 (OH)2 D3, an active form of vitamin D, was decreased in K-G6pc-/- mice. Interestingly, the administration of 1,25 (OH)2 D3 prevented the enhancement of intestinal gluconeogenesis and hepatic GK activity and blocked the accumulation of hepatic glycogen otherwise observed in K-G6pc-/- mice during fasting. ConclusionsA diminution in renal gluconeogenesis that is accompanied by a decrease in blood vitamin D promotes a novel repartition of EGP among glucose producing organs during fasting, featured by increased intestinal gluconeogenesis that leads to sparing glycogen stores in the liver. Our data suggest a possible involvement of a crosstalk between the kidneys and intestine (via the vitamin D system) and the intestine and liver (via a neural gut-brain axis), which might take place in the situations of deficient renal glucose production, such as chronic kidney disease.

(-)-Epicatechin and the Colonic 2,3-Dihydroxybenzoic Acid Metabolite Regulate Glucose Uptake, Glucose Production, and Improve Insulin Signaling in Renal NRK-52E Cells.

(-)-Epicatechin (EC) and main colonic phenolic acids derived from flavonoid intake, such as 2,3-dihydroxybenzoic acid (DHBA), 3,4-dihydroxyphenylacetic acid (DHPAA), 3-hydroxyphenylpropionic acid (HPPA), and vanillic acid (VA), have been suggested to exert beneficial effects in diabetes, although the mechanism for their actions remains unknown. In this study, the modulation of glucose homeostasis and insulin signaling by the mentioned compounds on renal proximal tubular NRK-52E cells is investigated. Levels of the glucose transporters SGLT-2 and GLUT-2, as well as glucose uptake, glucose production, and key proteins of the insulin pathways, namely insulin receptor (IR), insulin receptor substrate-1 (IRS-1), and PI3K/AKT pathway are analyzed. EC (5-20 μm) and DHBA (20 μm) reduced both renal glucose uptake and production. Interestingly, EC and DHBA did not modify the levels of SGLT-2 and GLUT-2, and modulated the expression of phosphoenolpyruvate carboxykinase via AKT leading to a diminished glucose production. EC and DHBA also enhanced the tyrosine phosphorylation and total IR and IRS-1 levels, and activated the PI3K/AKT pathway in NRK-52E cells. EC and DHBA regulate the renal glucose homeostasis by modulating both glucose uptake and production, and strengthen the insulin signaling by activating key proteins of that pathway in NRK-52E cells.

Endogenous Nutritive Support after Traumatic Brain Injury: Peripheral Lactate Production for Glucose Supply via Gluconeogenesis.

We evaluated the hypothesis that nutritive needs of injured brains are supported by large and coordinated increases in lactate shuttling throughout the body. To that end, we used dual isotope tracer ([6,6-2H2]glucose, i.e., D2-glucose, and [3-13C]lactate) techniques involving central venous tracer infusion along with cerebral (arterial [art] and jugular bulb [JB]) blood sampling. Patients with traumatic brain injury (TBI) who had nonpenetrating head injuries (n=12, all male) were entered into the study after consent of patients' legal representatives. Written and informed consent was obtained from healthy controls (n=6, including one female). As in previous investigations, the cerebral metabolic rate (CMR) for glucose was suppressed after TBI. Near normal arterial glucose and lactate levels in patients studied 5.7±2.2 days (range of days 2–10) post-injury, however, belied a 71% increase in systemic lactate production, compared with control, that was largely cleared by greater (hepatic+renal) glucose production. After TBI, gluconeogenesis from lactate clearance accounted for 67.1% of glucose rate of appearance (Ra), which was compared with 15.2% in healthy controls. We conclude that elevations in blood glucose concentration after TBI result from a massive mobilization of lactate from corporeal glycogen reserves. This previously unrecognized mobilization of lactate subserves hepatic and renal gluconeogenesis. As such, a lactate shuttle mechanism indirectly makes substrate available for the body and its essential organs, including the brain, after trauma. In addition, when elevations in arterial lactate concentration occur after TBI, lactate shuttling may provide substrate directly to vital organs of the body, including the injured brain.

Absence of intestinal gluconeogenesis in rats and dogs

We investigated the potential for intestinal gluconeogenesis in vivo by determining the arterio-venous balances of concentration and isotopic enrichment (IE) of [6,6-2H2]glucose across various organs. The gas chromatography-mass spectrometry data were integrated using a recently developed method that amplifies the apparent IE while improving the precision of the measurements. In 48 hr-fasted rats receiving a constant infusion of [6,6-2H2]glucose, we could not detect a difference in glucose IE across the intestine (n = 7, 4 pairs of samples per rat). To test whether deep hypoglycemia would induce intestinal glucose production, we studied acutely hepatectomized 48 hr-fasted dogs. When the liver was clamped, we injected a 1.1 mmol bolus of [6,6-2H2]glucose. Over the next 2 hr, arterial glucose concentration and IE decreased from ~ 5 mM to ~ 0.5 mM and from ~ 1.25% to ~ 0.25%, respectively (the later resulted from some glucose production in the kidney, demonstrated by a small detectable difference in glucose IE between arterial and renal vein plasma). However, the renal glucose production did not prevent deep hypoglycemia. In addition, there was no detectable difference in glucose IE or concentration between arterial and portal vein plasma (n = 5 dogs, 8 to 12 pairs of samples per dog). We conclude that there is no detectable intestinal gluconeogenesis in dogs and rats in vivo. Supported by NIH Roadmap grant 5 R33 DK070291.

Renal amino acid, fat and glucose metabolism in type 1 diabetic and non-diabetic humans: effects of acute insulin withdrawal

The aim of this study was to test the hypothesis that type 1 diabetes alters renal amino acid, glucose and fatty acid metabolism. We studied five C-peptide-negative, type 1 diabetic subjects during insulin replacement (glucose 5.6 mmol/l) and insulin deprivation (glucose 15.5 mmol/l) and compared them with six non-diabetic subjects. Leucine, phenylalanine, tyrosine, glucose and palmitate tracers were infused after an overnight fast and samples were obtained from the renal vein, femoral vein and femoral artery. Insulin deprivation significantly increased whole-body fluxes (20-25%) of phenylalanine, tyrosine and leucine, and leucine oxidation (50%). Kidney contributed 5-10% to the whole-body leucine and phenylalanine flux. A net uptake of phenylalanine, conversion of phenylalanine to tyrosine (5 micromol/min) and net release of tyrosine (approximately 5 micromol/min) occurred across the kidney. Whole-body (three-fold) and leg (two-fold) leucine transamination increased but amino acid metabolism in the kidney did not alter with diabetes or insulin deprivation. Insulin deprivation doubled endogenous glucose production, renal glucose production was unaltered by insulin deprivation and diabetes (ranging between 100 and 140 micromol/min). Renal palmitate exchange was unaltered by insulin deprivation. In conclusion, kidney post-absorptively accounts for 5-10% of whole-body protein turnover, 15-20% of leucine transamination and 10-15% of endogenous glucose production, and actively converts phenylalanine to tyrosine. During insulin deprivation, leg becomes a major site for leucine transamination but insulin deprivation does not affect renal phenylalanine, leucine, palmitate or glucose metabolism. Despite its key metabolic role, insulin deprivation in type 1 diabetic patients does not alter many of these metabolic functions.

Effects of hyperglycemia, glucagon, and epinephrine on renal glucose release in the conscious dog

The role of renal glucose production after an overnight fast and in response to different hormonal conditions has been debated. The aim of this study was to determine whether hyperglycemia, glucagon, or epinephrine can affect renal glucose production. In 18-hour fasted conscious dogs a pancreatic clamp initially fixed insulin and glucagon at basal levels, following which 1 of 4 protocols was instituted. In G+E glucagon (1.5 ng · kg −1 · min −1; portally) and epinephrine (50 ng · kg −1 · min −1; peripherally) were increased, in G glucagon was increased alone, in E epinephrine was increased alone, and in C neither were increased. In G, E, and C, glucose was infused to match the hyperglycemia in G+E (∼250 mg/dL). The average net renal glucose output during the last 2 hours was not different from the basal values in any group. Furthermore, the changes in unidirectional renal glucose production were not significantly different among groups. Therefore, after an overnight fast in the conscious dog, the kidneys do not significantly contribute to overall glucose production or respond to glucagon or epinephrine.

Bench-to-bedside review: glucose production from the kidney.

Data obtained from net organ balance studies of glucose production lead to the classic view according to which glucose homeostasis is mainly ensured by the liver, and renal glucose production only plays a significant role during acidosis and prolonged starvation. Renal glucose release and uptake, as well as the participation of gluconeogenic substrates in renal gluconeogenesis, were recently re-evaluated using systemic and renal arteriovenous balance of substrates in combination with deuterated glucose dilution. Data obtained using these methods lead one to reconsider the magnitude of renal glucose production as well as its role in various physiological and pathological circumstances. These findings now conduce one to consider that renal gluconeogenesis substantially participates in postabsorptive glucose production, and that its role in glucose homeostasis is of first importance.

Renal substrate metabolism and gluconeogenesis during hypoglycemia in humans.

To examine the potential contribution of precursor substrates to renal gluconeogenesis during hypoglycemia, 14 healthy subjects had arterialized hand vein and renal vein (under fluoroscopy) catheterized after an overnight fast. Net renal balance of lactate, glycerol, alanine, and glutamine was determined simultaneously with systemic and renal glucose kinetics using arteriovenous concentration differences and 6-[2H2]glucose tracer dilution. Renal plasma flow was measured by para-aminohippurate clearance and was converted to blood flow using the mathematical value (1-hematocrit). Arterial and renal vein samples were obtained in the postabsorptive state and during a 180-min hyperinsulinemic period during either euglycemia or hypoglycemia. Insulin increased from 49 +/- 14 to 130 +/- 25 pmol/l (hypoglycemia) and to 102 +/- 10 pmol/l (euglycemia). Arterial blood glucose decreased from 4.5 +/-0.2 to 3.0 +/- 0.1 mmol/l during hypoglycemia but did not change during euglycemia (4.3 +/- 0.2 mmol/l). After 150 min, endogenous glucose production reached a plateau value that was higher during hypoglycemia (10.3 +/0.6 micromol x kg(-1) x min(-1)) than during euglycemia (5.73 +/-0.6 micromol x kg(-1) x min(-1), P < 0.001). Hypoglycemia was associated with a rise in renal glucose production (RGP) from 3.0 +/- 0.7 to 5.4 +/- 0.6 micromol x kg(-1) x min(-1) (P < 0.05), although glucose utilization remained the same (2.0 +/- 0.8 vs. 2.1 +/-0.6 micromol x kg(-1) x min(-1)). As a result, net renal glucose output increased from 1.0 +/- 0.3 to 3.3 +/- 0.40 micromol x kg(-1) x min(-1). Elevations in net renal uptake of lactate (2.4 +/- 0.5 to 3.5 +/- 0.7 vs. 2.8 +/- 0.4 micromol x kg(-1) x min(-1)), glycerol (0.6 +/- 0.3 to 1.3 +/- 0.5 vs. 0.4 +/- 0.2 micromol x kg(-1) x min(-1)), and glutamine (0.7 +/- 0.2 to 1.1 +/- 0.3 vs. 0.1 +/- 0.3 micromol x kg(-1) x min(-1)) during hypoglycemia versus euglycemia (P < 0.05) could account for nearly 60% of all glucose carbons released in the renal vein during hypoglycemia. Our data indicate that extraction of circulating gluconeogenic precursors by the kidney is enhanced and responsible for a substantial fraction of the compensatory rise in RGP during sustained hypoglycemia. Increased renal gluconeogenesis from circulating substrates represents an additional physiological mechanism by which the decrease in blood glucose concentration is attenuated in humans.

Regulation of splanchnic and renal substrate supply by insulin in humans

To determine the effects of peripheral insulin infusion on total, hepatic, and renal glucose production and on the percent contribution to glucose production of gluconeogenesis versus glycogenolysis, 10 healthy subjects had arterialized hand and hepatic vein catheterization after an overnight fast and the results were compared with data from 12 age- and weight-matched subjects with renal vein catheterization during a 180-minute infusion of either insulin (0.25 mU/kg x min) with dextrose, or saline. Endogenous, hepatic, and renal glucose production was measured with [6,6(-2)H2]glucose, regional lactate, alanine, and glycerol balance by arteriovenous difference; hepatic blood flow by indocyanine green clearance; and renal blood flow by p-aminohippurate clearance, before and every 30 minutes during each infusion period. Insulin increased from about 42 to 98 pmol/L and blood glucose remained constant in all studies (3.8 +/- 0.2 v4.4 +/- 0.1 micromol/ml, hepatic vrenal vein). In response to insulin infusion, endogenous, hepatic, and renal glucose production decreased immediately (30 minutes) and reached a lower plateau value (10.8 +/- 0.8 v6.4 +/- 0.7, 10.4 +/- 1.1 v7.8 +/- 1.0, and 2.8 +/- 0.6 v 1.5 +/- 0.6 micromol/kg x min, respectively) between 120 and 180 minutes (all P < .05). Net renal uptake of lactate (2.4 +/- 0.4 v0.9 +/- 0.6) decreased earlier (30 minutes) and returned to baseline between 120 and 180 minutes (2.4 +/- 0.5 micromol/kg x min), whereas net splanchnic uptake of lactate (5.7 +/- 0.7 v 0.7 +/- 0.6) and alanine (1.8 +/- 0.1 v 1.0 +/- 0.5 micromol/kg x min) decreased later (120 to 180 minutes). Net renal (0.3 +/- 0.1 v 0.1 +/- 0.1) and splanchnic (0.7 +/- 0.3 v 0.4 +/- 0.2 micromol/kg x min) glycerol uptake decreased 90 to 180 minutes after insulin and increased (P < .05) with saline infusion (0.4 +/- 0.1 v0.6 +/- 0.3 and 1.0 +/- 0.5 v1.8 +/- 0.4 micromol/kg x min, respectively). These data indicate that the rapid suppression of endogenous glucose production by insulin reflects primarily a decrease in hepatic glucose release, most likely due to inhibition of net glycogenolysis, combined with suppression of renal gluconeogenesis. Inhibition of hepatic gluconeogenesis presumably occurs later during hyperinsulinemia. We conclude that peripheral insulin, in addition to its inhibition of glycogen degradation, regulates endogenous glucose production, in part, by modifying the splanchnic and renal substrate supply.