Background and aims: Hyperglucagonemia is a characteristic feature of type 2 diabetes mellitus (T2DM). We examined the effect of chronic (48-72 h) physiologic increase (+50 mg/dl) in plasma glucose concentration on suppression of plasma glucagon concentration by insulin and by hyperglycemia in normal glucose tolerance (NGT) individuals. Materials and methods: Study One: 16 NGT subjects received OGTT and 3-step hyperinsulinemic (10, 20, 40 mU/ m(2)center dot min) euglycemic clamp before and after 48 hour glucose infusion to increase plasma glucose by similar to 50 mg/dl. Study Two: 20 NGT subjects received OGTT and 2-step hyperglycemic (+125 and + 300 mg/dl) clamp before and after 72 hour glucose infusion. Plasma insulin, C-peptide and glucagon concentrations were measured during OGTT, euglycemic hyperinsulinemic and hyperglycemic clamps. Ratio of plasma glucagon/insulin was used as an index of insulin-mediated suppression of glucagon secretion. Results: During all 3 insulin clamp steps (Study 1), plasma glucagon concentration was increased compared to baseline study, and plasma glucagon/insulin ratio was significantly reduced by 24 % (p < 0.05). The rate of insulin-stimulated glucose disposal was inversely correlated with plasma glucagon/insulin ratio (r = -0.44, p < 0.05) and with glucagon AUC (r = -0.48, p < 0.05). During the 2-step hyperglycemic clamp (Study 2) plasma glucagon was similar before and after 72 h of glucose infusion; however, glucagon/insulin ratio was significantly reduced (p < 0.05). Incremental area under plasma insulin curve during the first (r = -0.74, p < 0.001) and second (r = -0.85, p < 0.001) hyperglycemic clamp steps was strongly and inversely correlated with plasma glucagon/insulin ratio. Conclusion: Sustained (48-72 h) physiologic hyperglycemia (+50 mg/dl) caused whole body insulin resistance and impaired insulin-mediated suppression of glucagon secretion, suggesting a role for glucotoxicity in development of hyperglucagonemia in T2DM.

OBJECTIVE Sodium–glucose cotransporter 2 (SGLT2) inhibition causes an increase in endogenous glucose production (EGP). However, the mechanisms are unclear. We studied the effect of SGLT2 inhibitors on EGP in subjects with type 2 diabetes (T2D) and without diabetes (non-DM) in kidney transplant recipients with renal denervation. RESEARCH DESIGN AND METHODS Fourteen subjects who received a renal transplant (six with T2D [A1C 7.2 ± 0.1%] and eight non-DM [A1C 5.6 ± 0.1%) underwent measurement of EGP with [3-3H]glucose infusion following dapagliflozin (DAPA) 10 mg or placebo. Plasma glucose, insulin, C-peptide, glucagon, and titrated glucose-specific activity were measured. RESULTS Following placebo in T2D, fasting plasma glucose (FPG) (143 ± 14 to 124 ± 10 mg/dL; P = 0.02) and fasting plasma insulin (12 ± 2 to 10 ± 1.1 μU/mL; P < 0.05) decreased; plasma glucagon was unchanged, and EGP declined. After DAPA in T2D, FPG (143 ± 15 to 112 ± 9 mg/dL; P = 0.01) and fasting plasma insulin (14 ± 3 to 11 ± 2 μU/mL; P = 0.02) decreased, and plasma glucagon increased (all P < 0.05 vs. placebo). EGP was unchanged from baseline (2.21 ± 0.19 vs. 1.96 ± 0.14 mg/kg/min) in T2D (P < 0.001 vs. placebo). In non-DM following DAPA, FPG and fasting plasma insulin decreased, and plasma glucagon was unchanged. EGP was unchanged from baseline (1.85 ± 0.10 to 1.78 ± 0.10 mg/kg/min) after DAPA, whereas EGP declined significantly with placebo. When the increase in EGP production following DAPA versus placebo was plotted against the difference in urinary glucose excretion (UGE) for all patients, a strong correlation (r = 0.824; P < 0.001) was observed. CONCLUSIONS Renal denervation in patients who received a kidney transplant failed to block the DAPA-mediated stimulation of EGP in both individuals with T2D and non-DM subjects. The DAPA-stimulated rise in EGP is strongly related to the increase in UGE, blunting the decline in FPG.

The aim of the current study was to evaluate the effect of sustained physiologic increase of ∼50 mg/dL in plasma glucose concentration on insulin secretion in normal glucose-tolerant (NGT) subjects. Twelve NGT subjects without family history of type 2 diabetes mellitus (T2DM; FH-) and 8 NGT with family history of T2DM (FH+) received an oral glucose tolerance test and two-step hyperglycemic clamp (100 and 300 mg/dL) followed by intravenous arginine bolus before and after 72-h glucose infusion. Fasting plasma glucose increased from 94 ± 2 to 142 ± 4 mg/dL for 72 h. First-phase insulin secretion (0-10 min) increased by 70%, while second-phase insulin secretion during the first (10-80 min) and second (90-160 min) hyperglycemic clamp steps increased by 3.8-fold and 1.9-fold, respectively, following 72 h of physiologic hyperglycemia. Insulin sensitivity during hyperglycemic clamp declined by ∼30% and ∼55% (both P < 0.05), respectively, during the first and second hyperglycemic clamp steps. Insulin secretion/insulin resistance (disposition) index declined by 60% (second clamp step) and by 62% following arginine (both P < 0.005) following 72-h glucose infusion. The effect of 72-h glucose infusion on insulin secretion and insulin sensitivity was similar in subjects with and without FH of T2DM. Following 72 h of physiologic hyperglycemia, metabolic clearance rate of insulin was markedly reduced (P < 0.01). These results demonstrate that sustained physiologic hyperglycemia for 72 h 1) increases absolute insulin secretion but impairs β-cell function, 2) causes insulin resistance, and 3) reduces metabolic clearance rate of insulin.

Recently, novel non-glycemic effects of glucagon have been described. Although short-term glucagon infusion is well known to elevate plasma glucose levels, long-term effect of increased plasma glucagon on glucose and lipid metabolism is unclear. The aim of the present study was to evaluate the effect of 12-hour glucagon infusion on hepatic glucose production and lipid metabolism in healthy NGT individuals. 8 NGT subjects (5M/3F, age=35± 5 years, BMI = 24 ± 1 kg/m2, HbA1c 5.2± 0.1%) received an 2-hour (75gram) OGTT. On a different day subjects received a 12-hour (6PM to 6 AM) glucagon infusion (3ng/kg/minutes) with the measurement of hepatic glucose production (HGP) with 3-3H-glucose on the following morning from 6-10 AM. HGP in glucagon infused subjects was compared to values in 20 age/gender/weight matched NGT subjects studied after an overnight fast from 6-10 AM. Plasma glucose, insulin, C-peptide, glucagon, and FFA concentrations were obtained every 15 minutes during OGTT. Plasma glucagon concentrations increased from 40 ± 4 to 120 ± 34 pg/ml at 6 AM. Plasma glucose increased 2 hours after the start of infusion from 95 ± 6 to 111 ± 6 mg/dl (p<0.005); after 12 hours of glucagon infusion the plasma glucose concentration declined to the mean baseline levels. After 12-hour glucagon infusion (6 AM), plasma insulin and C-peptide were not significantly changed. Basal hepatic glucose production was significantly higher following prolonged (12-hour) glucagon infusion compared to NGT control subjects following 12-hour overnight fast (3.1 ± 0.1 vs. 2.2 ± 0.2 mg/kg/minutes, p<0.05). Plasma FFA concentrations did not change following 12-hour glucagon infusion (0.629±0.1 vs. 0.670±0.2mml/l, p=ns). Thus 12-hour glucagon infusion led to higher basal rate of HGP, but unchanged plasma FFA levels. These results demonstrate that prolonged physiologic hyperglucagonemia results in a transient elevation of plasma glucose concentration but sustained increase in hepatic glucose production. Disclosure X. Chen: None. A. Merovci: None. E. Case: None. R.A. DeFronzo: Advisory Panel; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Elcelyx Therapeutics, Inc., Intarcia Therapeutics, Inc., Janssen Pharmaceuticals, Inc., Novo Nordisk Inc. Research Support; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Janssen Pharmaceuticals, Inc., Merck & Co., Inc. Speaker's Bureau; Self; AstraZeneca, Novo Nordisk Inc. D. Tripathy: None.

Hyperglycemia adversely affects skeletal muscle and hepatic insulin sensitivity (glucotoxicity). However, the effect of prolonged hyperglycemia on glucose and insulin-mediated suppression of glucagon is not known. The aim of the present study was to evaluate effect of a chronic (72 hours) physiologic increase (+45 mg/dl) in plasma glucose concentration on the suppression of plasma glucagon concentration in healthy NGT individuals: 12 without family history of T2DM (FH-) (9M/3F, age = 50± 4 years, BMI = 27 ± 1 kg/m2) and 8 with FH of T2DM (FH+) (4M/4F, age = 48±2, BMI = 26±1 kg/m2). Subjects received an OGTT and 2-step hyperglycemic (+125 and +300 mg/dl) clamp (duration of each step = 80 minutes) before and after 72-hour glucose infusion. Plasma insulin and C-peptide concentrations were obtained every 2-5 minutes during each hyperglycemic clamp step and plasma glucagon concentrations were measured every 10 minutes. The ratio of insulin/glucagon was measured and used as an index of insulin-medicated suppression of plasma glucagon. FPG concentration increased from 97±4 to 140±4 mg/dl during the 72-hour glucose infusion. Following chronic glucose infusion, plasma insulin levels were significantly higher during the basal state and during each hyperglycemic clamp step (by 59% and 78%) during the 0-80 and 80-160 min time periods, respectively. There was no difference in plasma glucagon levels following chronic glucose infusion. However, the plasma insulin/glucagon ratio was significantly higher during the fasting state (by 76%) and during the first (by 128%) and second (by 178%) hyperglycemic clamp steps. There was no difference in the effect of chronic glucose infusion on glucagon secretion between FH+ and FH-subjects. These results demonstrate that sustained physiologic hyperglycemia for 72 hours (i.e., glucotoxicity) impairs insulin-mediated suppression of glucagon, and could contribute to fasting and post-prandial hyperglycemia in T2DM patients. Disclosure A. Merovci: None. X. Chen: None. R.A. DeFronzo: Advisory Panel; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Elcelyx Therapeutics, Inc., Intarcia Therapeutics, Inc., Janssen Pharmaceuticals, Inc., Novo Nordisk Inc. Research Support; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Janssen Pharmaceuticals, Inc., Merck & Co., Inc. Speaker's Bureau; Self; AstraZeneca, Novo Nordisk Inc. D. Tripathy: None. Funding National Institutes of Health