RESUMO
The second meal phenomenon refers to the improvement in glucose tolerance seen following a second identical meal. We previously showed that 4 hours of morning (AM) hyperinsulinemia, but not hyperglycemia, enhanced hepatic glucose uptake (HGU) and glycogen storage during an afternoon (PM) hyperinsulinemic hyperglycemic clamp (HIHG). Our current aim was to determine if the duration or pattern of morning hyperinsulinemia is important for the PM response to a HIHG clamp. To determine this, we administered the same total amount of insulin either over 2h in the first half of the morning (Ins2h-A), over 2h in the 2nd half of the morning (Ins2h-B), or over the entire 4h (Ins4h) of the morning. In the 4h PM period, all three groups had 4x basal insulin, 2x basal glycemia, and portal glucose infusion to simulate a meal. During the PM clamp, there was a marked increase in the mean hepatic glucose uptake and hepatic glycogen synthesis in the Ins4h group compared to the Ins2h-A and Ins2h-B groups, despite matched hepatic glucose and insulin loads. Thus, the longer duration (Ins4h) of mild hyperinsulinemia in the morning seems to be the key to much greater liver glucose uptake during the PM clamp.
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The purpose of this study was to assess insulin-stimulated gene expression in canine skeletal muscle with a particular focus on NPPC, the gene that encodes C-type natriuretic peptide, a key hormonal regulator of cardiometabolic function. Four conscious canines underwent hyperinsulinemic, euglycemic clamp studies. Skeletal muscle biopsy and arterial plasma samples were collected under basal and insulin-stimulated conditions. Bulk RNA sequencing of muscle tissue was performed to identify differentially expressed genes between these 2 steady-state conditions. Our results showed that NPPC was the most highly expressed gene in skeletal muscle in response to insulin infusion, rising 4-fold between basal and insulin-stimulated conditions. In support of our RNA sequencing data, we found that raising the plasma insulin concentration 15-fold above basal elicited a 2-fold (P = 0.0001) increase in arterial plasma concentrations of N-terminal prohormone C-type natriuretic peptide. Our data suggest that insulin may play a role in stimulating secretion of C-type natriuretic peptide by skeletal muscle. In this context, C-type natriuretic peptide may act in a paracrine manner to facilitate muscle-vascular bed crosstalk and potentiate insulin-mediated vasodilation. This could serve to enhance insulin and glucose delivery, particularly in the postprandial absorptive state.
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Bromocriptine mesylate treatment was examined in dogs fed a high fat diet (HFD) for 8 wk. After 4 wk on HFD, daily bromocriptine (Bromo; n = 6) or vehicle (CTR; n = 5) injections were administered. Oral glucose tolerance tests were performed before beginning HFD (OGTT1), 4 wk after HFD began (Bromo only), and after 7.5 wk on HFD (OGTT3). After 8 wk on HFD, clamp studies were performed, with infusion of somatostatin and intraportal replacement of insulin (4× basal) and glucagon (basal). From 0 to 90 min (P1), glucose was infused via peripheral vein to double the hepatic glucose load; and from 90 to 180 min (P2), glucose was infused via the hepatic portal vein at 4 mg·kg-1·min-1, with the HGL maintained at 2× basal. Bromo decreased the OGTT glucose ΔAUC0-30 and ΔAUC0-120 by 62 and 27%, respectively, P < 0.05 for both) without significantly altering the insulin response. Bromo dogs exhibited enhanced net hepatic glucose uptake (NHGU) compared with CTR (~33 and 21% greater, P1 and P2, respectively, P < 0.05). Nonhepatic glucose uptake (non-HGU) was increased ~38% in Bromo in P2 (P < 0.05). Bromo vs. CTR had higher (P < 0.05) rates of glucose infusion (36 and 30%) and non-HGU (~40 and 27%) than CTR during P1 and P2, respectively. In Bromo vs. CTR, hepatic 18:0/16:0 and 16:1/16:0 ratios tended to be elevated in triglycerides and were higher (P < 0.05) in phospholipids, consistent with a beneficial effect of bromocriptine on liver fat accumulation. Thus, bromocriptine treatment improved glucose disposal in a glucose-intolerant model, enhancing both NHGU and non-HGU.
Assuntos
Glicemia/efeitos dos fármacos , Bromocriptina/farmacologia , Dieta Hiperlipídica , Agonistas de Dopamina/farmacologia , Intolerância à Glucose/metabolismo , Fígado/efeitos dos fármacos , Animais , Glicemia/metabolismo , Cães , Ácidos Graxos não Esterificados/metabolismo , Glucagon/efeitos dos fármacos , Glucagon/metabolismo , Glucose/metabolismo , Técnica Clamp de Glucose , Teste de Tolerância a Glucose , Glicogênio/metabolismo , Veias Hepáticas , Insulina/metabolismo , Ácido Láctico/metabolismo , Fígado/metabolismo , Veia Porta , SomatostatinaRESUMO
AIMS: We previously quantified the hypoglycaemia-sparing effect of portal vs peripheral human insulin delivery. The current investigation aimed to determine whether a bioequivalent peripheral vein infusion of a hepatopreferential insulin analog, insulin-406, could similarly protect against hypoglycaemia. MATERIALS AND METHODS: Dogs received human insulin infusions into either the hepatic portal vein (PoHI, n = 7) or a peripheral vein (PeHI, n = 7) for 180 minutes at four-fold the basal secretion rate (6.6 pmol/kg/min) in a previous study. Insulin-406 (Pe406, n = 7) was peripherally infused at 6.0 pmol/kg/min, a rate determined to decrease plasma glucose by the same amount as with PoHI infusion during the first 60 minutes. Glucagon was fixed at basal concentrations, mimicking the diminished α-cell response seen in type 1 diabetes. RESULTS: Glucose dropped quickly with PeHI infusion, reaching 41 ± 3 mg/dL at 60 minutes, but more slowly with PoHI and Pe406 infusion (67 ± 2 and 72 ± 4 mg/dL, respectively; P < 0.01 vs PeHI for both). The hypoglycaemic nadir (c. 40 mg/dL) occurred at 60 minutes with PeHI infusion vs 120 minutes with PoHI and Pe406 infusion. ΔAUCepinephrine during the 180-minute insulin infusion period was two-fold higher with PeHI infusion compared with PoHI and Pe406 infusion. Glucose production (mg/kg/min) was least suppressed with PeHI infusion (Δ = 0.79 ± 0.33) and equally suppressed with PoHI and Pe406 infusion (Δ = 1.16 ± 0.21 and 1.18 ± 0.17, respectively; P = NS). Peak glucose utilization (mg/kg/min) was highest with PeHI infusion (4.94 ± 0.17) and less with PoHI and Pe406 infusion (3.58 ± 0.58 and 3.26 ± 0.08, respectively; P < 0.05 vs Pe for both). CONCLUSIONS: Peripheral infusion of hepatopreferential insulin can achieve a metabolic profile that closely mimics portal insulin delivery, which reduces the risk of hypoglycaemia compared with peripheral insulin infusion.
Assuntos
Hipoglicemiantes , Insulina Regular Humana , Insulina , Veia Porta/metabolismo , Animais , Glicemia/análise , Glicemia/metabolismo , Diabetes Mellitus Tipo 1 , Cães , Gluconeogênese , Humanos , Hipoglicemia/metabolismo , Hipoglicemiantes/administração & dosagem , Hipoglicemiantes/farmacologia , Infusões Intravenosas , Insulina/administração & dosagem , Insulina/análogos & derivados , Insulina/sangue , Insulina/farmacologia , Insulina Regular Humana/administração & dosagem , Insulina Regular Humana/farmacologia , Fígado/metabolismo , MasculinoRESUMO
Although insulin resistance consistently occurs with type 1 diabetes, its predominant driver is uncertain. We therefore determined the relative contributions of hyperglycemia and iatrogenic hyperinsulinemia to insulin resistance using hyperinsulinemic-euglycemic clamps in three participant groups (n = 10/group) with differing insulinemia and glycemia: healthy control subjects (euinsulinemia and euglycemia), glucokinase-maturity-onset diabetes of the young (GCK-MODY; euinsulinemia and hyperglycemia), and type 1 diabetes (hyperinsulinemia and hyperglycemia matching GCK-MODY). We assessed the contribution of hyperglycemia by comparing insulin sensitivity in control and GCK-MODY and the contribution of hyperinsulinemia by comparing GCK-MODY and type 1 diabetes. Hemoglobin A1c was normal in control subjects and similarly elevated for type 1 diabetes and GCK-MODY. Basal insulin levels in control subjects and GCK-MODY were nearly equal but were 2.5-fold higher in type 1 diabetes. Low-dose insulin infusion suppressed endogenous glucose production similarly in all groups and suppressed nonesterified fatty acids similarly between control subjects and GCK-MODY, but to a lesser extent for type 1 diabetes. High-dose insulin infusion stimulated glucose disposal similarly in control subjects and GCK-MODY but was 29% and 22% less effective in type 1 diabetes, respectively. Multivariable linear regression showed that insulinemia-but not glycemia-was significantly associated with muscle insulin sensitivity. These data suggest that iatrogenic hyperinsulinemia predominates in driving insulin resistance in type 1 diabetes.
Assuntos
Diabetes Mellitus Tipo 2/sangue , Diabetes Mellitus Tipo 2/fisiopatologia , Hiperglicemia/fisiopatologia , Hiperinsulinismo/fisiopatologia , Resistência à Insulina/fisiologia , Adolescente , Adulto , Feminino , Humanos , Hiperglicemia/sangue , Hiperinsulinismo/sangue , Masculino , Pessoa de Meia-Idade , Modelos Teóricos , Adulto JovemRESUMO
It is unknown whether activation of hepato-portal vein (PV) glucose sensors plays a role in incretin hormone amplification of oral glucose-stimulated insulin secretion (GSIS). In previous studies, PV glucose infusion increased GSIS through unknown mechanisms, perhaps neural stimulation of pancreatic ß-cells and/or stimulation of gut incretin hormone release. Thus, there could be a difference in the incretin effect when comparing GSIS with portal rather than leg vein (LV) glucose infusion. Plasma insulin and incretin hormones were studied in six overnight-fasted dogs. An oral glucose tolerance test (OGTT) was administered, and then 1 and 2 wk later the arterial plasma glucose profile from the OGTT was mimicked by infusing glucose into either the PV or a LV. The arterial glucose levels were nearly identical between groups (AUCs within 1% of each other). Oral glucose administration increased arterial GLP-1 and GIP levels by more than sixfold, whereas they were not elevated by PV or LV glucose infusion. Oral glucose delivery was associated with only a small incretin effect (arterial insulin and C-peptide were 21 ± 23 and 24 ± 17% greater, respectively, during the 1st hour with oral compared with PV glucose and 14 ± 37 and 13 ± 35% greater, respectively, in oral versus LV; PV versus LV responses were not significantly different from each other). Thus, following an OGTT incretin hormone release did not depend on activation of PV glucose sensors, and the insulin response was not greater with PV compared with LV glucose infusion in the dog. The small incretin effect points to species peculiarities, which is perhaps related to diet.
Assuntos
Glucose/farmacologia , Incretinas/metabolismo , Veia Porta/metabolismo , Animais , Glicemia/análise , Peptídeo C/sangue , Cães , Feminino , Polipeptídeo Inibidor Gástrico/sangue , Peptídeo 1 Semelhante ao Glucagon/sangue , Glucose/administração & dosagem , Teste de Tolerância a Glucose , Membro Posterior/irrigação sanguínea , Infusões Intravenosas , Insulina/sangue , Insulina/metabolismo , Masculino , Veia Porta/química , Fluxo Sanguíneo Regional , VeiasRESUMO
We observed that a 4-h morning (AM) duodenal infusion of glucose versus saline doubled hepatic glucose uptake (HGU) and storage during a hyperinsulinemic-hyperglycemic (HIHG) clamp that afternoon (PM). To separate the effects of AM hyperglycemia versus AM hyperinsulinemia on the PM response, we used hepatic balance and tracer ([3-3H]glucose) techniques in conscious dogs. From 0 to 240 min, dogs underwent a euinsulinemic-hyperglycemic (GLC; n = 7) or hyperinsulinemic-euglycemic (INS; n = 8) clamp. Tracer equilibration and basal sampling occurred from 240 to 360 min, followed by an HIHG clamp (360-600 min; four times basal insulin, two times basal glycemia) with portal glucose infusion (4 mg â kg-1 â min-1). In the HIHG clamp, HGU (5.8 ± 0.9 vs. 3.3 ± 0.3 mg â kg-1 â min-1) and net glycogen storage (6.0 ± 0.8 vs. 2.9 ± 0.5 mg â kg-1 â min-1) were approximately twofold greater in INS than in GLC. PM hepatic glycogen content (1.9 ± 0.2 vs. 1.3 ± 0.2 g/kg body weight) and glycogen synthase (GS) activity were also greater in INS versus GLC, whereas glycogen phosphorylase (GP) activity was reduced. Thus AM hyperinsulinemia, but not AM hyperglycemia, enhanced the HGU response to a PM HIHG clamp by augmenting GS and reducing GP activity. AM hyperinsulinemia can prime the liver to extract and store glucose more effectively during subsequent same-day meals, potentially providing a tool to improve glucose control.
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Ritmo Circadiano/fisiologia , Glucose/metabolismo , Hiperinsulinismo/metabolismo , Glicogênio Hepático/metabolismo , Animais , Metabolismo dos Carboidratos , Cães , Feminino , Glicogênio/metabolismo , Hiperinsulinismo/sangue , Insulina/sangue , Fígado/metabolismo , Masculino , Fatores de TempoRESUMO
We evaluated the hepatic and nonhepatic responses to glucose-responsive insulin (GRI). Eight dogs received GRI or regular human insulin (HI) in random order. A primed, continuous intravenous infusion of [3-3H]glucose began at -120 min. Basal sampling (-30 to 0 min) was followed by two study periods (150 min each), clamp period 1 (P1) and clamp period 2 (P2). At 0 min, somatostatin and GRI (36 ± 3 pmol/kg/min) or HI (1.8 pmol/kg/min) were infused intravenously; basal glucagon was replaced intraportally. Glucose was infused intravenously to clamp plasma glucose at 80 mg/dL (P1) and 240 mg/dL (P2). Whole-body insulin clearance and insulin concentrations were not different in P1 versus P2 with HI, but whole-body insulin clearance was 23% higher and arterial insulin 16% lower in P1 versus P2 with GRI. Net hepatic glucose output was similar between treatments in P1. In P2, both treatments induced net hepatic glucose uptake (HGU) (HI mean ± SEM 2.1 ± 0.5 vs. 3.3 ± 0.4 GRI mg/kg/min). Nonhepatic glucose uptake in P1 and P2, respectively, differed between treatments (2.6 ± 0.3 and 7.4 ± 0.6 mg/kg/min with HI vs. 2.0 ± 0.2 and 8.1 ± 0.8 mg/kg/min with GRI). Thus, glycemia affected GRI but not HI clearance, with resultant differential effects on HGU and nonHGU. GRI holds promise for decreasing hypoglycemia risk while enhancing glucose uptake under hyperglycemic conditions.
Assuntos
Avaliação Pré-Clínica de Medicamentos , Drogas em Investigação/efeitos adversos , Metabolismo Energético/efeitos dos fármacos , Hipoglicemiantes/efeitos adversos , Insulina Regular Humana/análogos & derivados , Fígado/efeitos dos fármacos , Absorção Fisiológica/efeitos dos fármacos , Animais , Glicemia/análise , Glicemia/metabolismo , Cães , Relação Dose-Resposta a Droga , Drogas em Investigação/administração & dosagem , Drogas em Investigação/farmacocinética , Gluconeogênese/efeitos dos fármacos , Técnica Clamp de Glucose , Glicosilação , Humanos , Hiperglicemia/metabolismo , Hiperglicemia/prevenção & controle , Hipoglicemia/induzido quimicamente , Hipoglicemia/metabolismo , Hipoglicemia/prevenção & controle , Hipoglicemiantes/administração & dosagem , Hipoglicemiantes/sangue , Hipoglicemiantes/farmacocinética , Infusões Intravenosas , Insulina Regular Humana/administração & dosagem , Insulina Regular Humana/efeitos adversos , Insulina Regular Humana/farmacocinética , Fígado/metabolismo , Masculino , Taxa de Depuração Metabólica , Distribuição Aleatória , Somatostatina/administração & dosagem , Somatostatina/efeitos adversosRESUMO
The contribution of hormone-independent counterregulatory signals in defense of insulin-induced hypoglycemia was determined in adrenalectomized, overnight-fasted conscious dogs receiving hepatic portal vein insulin infusions at a rate 20-fold basal. Either euglycemia was maintained (group 1) or hypoglycemia (≈45 mg/dl) was allowed to occur. There were three hypoglycemic groups: one in which hepatic autoregulation against hypoglycemia occurred in the absence of sympathetic nervous system input (group 2), one in which autoregulation occurred in the presence of norepinephrine (NE) signaling to fat and muscle (group 3), and one in which autoregulation occurred in the presence of NE signaling to fat, muscle, and liver (group 4). Average net hepatic glucose balance (NHGB) during the last hour for groups 1-4 was -0.7 ± 0.1, 0.3 ± 0.1 (P < 0.01 vs. group 1), 0.7 ± 0.1 (P = 0.01 vs. group 2), and 0.8 ± 0.1 (P = 0.7 vs. group 3) mg·kg-1·min-1, respectively. Hypoglycemia per se (group 2) increased NHGB by causing an inhibition of net hepatic glycogen synthesis. NE signaling to fat and muscle (group 3) increased NHGB further by mobilizing gluconeogenic precursors resulting in a rise in gluconeogenesis. Lowering glucose per se decreased nonhepatic glucose uptake by 8.9 mg·kg-1·min-1, and the addition of increased neural efferent signaling to muscle and fat blocked glucose uptake further by 3.2 mg·kg-1·min-1 The addition of increased neural efferent input to liver did not affect NHGB or nonhepatic glucose uptake significantly. In conclusion, even in the absence of increases in counterregulatory hormones, the body can defend itself against hypoglycemia using glucose autoregulation and increased neural efferent signaling, both of which stimulate hepatic glucose production and limit glucose utilization.
Assuntos
Glicemia/efeitos dos fármacos , Hipoglicemia/metabolismo , Hipoglicemiantes/farmacologia , Insulina/farmacologia , Fígado/efeitos dos fármacos , Tecido Adiposo/metabolismo , Adrenalectomia , Animais , Glicemia/metabolismo , Cães , Gluconeogênese/efeitos dos fármacos , Glucose/metabolismo , Técnica Clamp de Glucose , Homeostase , Hipoglicemia/induzido quimicamente , Infusões Intravenosas , Fígado/metabolismo , Glicogênio Hepático/metabolismo , Músculo Esquelético/metabolismo , Norepinefrina/metabolismo , Veia Porta , Sistema Nervoso SimpáticoRESUMO
We used hepatic balance and tracer ([3H]glucose) techniques to examine the impact of "breakfast" on hepatic glucose metabolism later in the same day. From 0-240 min, 2 groups of conscious dogs (n = 9 dogs/group) received a duodenal infusion of glucose (GLC) or saline (SAL), then were fasted from 240-360 min. Three dogs from each group were euthanized and tissue collected at 360 min. From 360-600 min, the remaining dogs underwent a hyperinsulinemic (4× basal) hyperglycemic clamp (arterial blood glucose 146 ± 2 mg/dL) with portal GLC infusion. The total GLC infusion rate was 14% greater in dogs infused with GLC than in those receiving SAL (AUC360-600min 2,979 ± 296 vs. 2,597 ± 277 mg/kg, respectively). The rates of hepatic glucose uptake (5.8 ± 0.8 vs. 3.2 ± 0.3 mg â kg-1 â min-1) and glycogen storage (4.7 ± 0.6 vs. 2.9 ± 0.3 mg â kg-1 â min-1) during the clamp were markedly greater in dogs receiving GLC compared with those receiving SAL. Hepatic glycogen content was â¼50% greater, glycogen synthase activity was â¼50% greater, glycogen phosphorylase activity was â¼50% lower, and the amount of phosphorylated glycogen synthase was 34% lower, indicating activation of the enzyme, in dogs receiving GLC compared with those receiving SAL. Thus, morning GLC primed the liver to extract and store more glucose in the presence of hyperinsulinemic hyperglycemia later in the same day, indicating that breakfast enhances the liver's role in glucose disposal in subsequent same-day meals.
Assuntos
Glicemia/metabolismo , Desjejum , Glicogênio Hepático/metabolismo , Fígado/metabolismo , Animais , Western Blotting , Cães , Duodeno , Jejum/metabolismo , Feminino , Glucoquinase/efeitos dos fármacos , Glucoquinase/metabolismo , Glucose/metabolismo , Glucose/farmacologia , Técnica Clamp de Glucose , Glicogênio/metabolismo , Glicogênio Fosforilase/efeitos dos fármacos , Glicogênio Fosforilase/genética , Glicogênio Sintase/efeitos dos fármacos , Glicogênio Sintase/metabolismo , Fígado/efeitos dos fármacos , Masculino , Fosfoproteínas/efeitos dos fármacos , Fosfoproteínas/metabolismo , Reação em Cadeia da Polimerase em Tempo Real , Edulcorantes/farmacologiaRESUMO
Insulin resistance occurs during various stages of the estrus cycle in dogs. To quantify the effects of proestrus-estrus (PE) and determine whether PE affects liver insulin sensitivity, 11 female mongrel dogs were implanted with sampling and intraportal infusion catheters. Five of the dogs (PE group) entered proestrus after surgery; those remaining in anestrus were controls. The dogs were fasted overnight, [3-(3)H]glucose and somatostatin were infused through peripheral veins, and glucagon was infused intraportally. Insulin was infused intraportally, with the rate adjusted to maintain arterial plasma glucose at basal levels (PE, 294±25 µU/kg/min; control, 223±21 µU/kg/min). Subsequently the insulin infusion rate was increased by 0.2 mU/kg/min for 120 min (P1) and then to 1.5 mU/kg/min for the last 120 min (P2); glucose was infused peripherally as needed to maintain euglycemia. Insulin concentrations did not differ between groups at any time; they increased 3 µU/mL over baseline during P1 and to 3 times baseline during P2. The glucose infusion rate in PE dogs during P2 was 63% of that in control dogs. Net hepatic glucose output and the endogenous glucose production rate declined 40% to 50% from baseline in both groups during P1; during P2, both groups exhibited a low rate of net hepatic glucose uptake with full suppression of endogenous glucose production. The glucose disappearance rate during P1 and P2 was 35% greater in control than PE dogs. Therefore, PE in canines is associated with loss of nonhepatic (primarily muscle) but not hepatic insulin sensitivity.
Assuntos
Cães/metabolismo , Estro/metabolismo , Insulina/metabolismo , Fígado/metabolismo , Proestro/metabolismo , Animais , Resistência à InsulinaRESUMO
Hypoglycemia limits optimal glycemic control in type 1 diabetes mellitus (T1DM), making novel strategies to mitigate it desirable. We hypothesized that portal (Po) vein insulin delivery would lessen hypoglycemia. In the conscious dog, insulin was infused into the hepatic Po vein or a peripheral (Pe) vein at a rate four times of basal. In protocol 1, a full counterregulatory response was allowed, whereas in protocol 2, glucagon was fixed at basal, mimicking the diminished α-cell response to hypoglycemia seen in T1DM. In protocol 1, glucose fell faster with Pe insulin than with Po insulin, reaching 56 ± 3 vs. 70 ± 6 mg/dL (P = 0.04) at 60 min. The change in area under the curve (ΔAUC) for glucagon was similar between Pe and Po, but the peak occurred earlier in Pe. The ΔAUC for epinephrine was greater with Pe than with Po (67 ± 17 vs. 36 ± 14 ng/mL/180 min). In protocol 2, glucose also fell more rapidly than in protocol 1 and fell faster in Pe than in Po, reaching 41 ± 3 vs. 67 ± 2 mg/dL (P < 0.01) by 60 min. Without a rise in glucagon, the epinephrine responses were much larger (ΔAUC of 204 ± 22 for Pe vs. 96 ± 29 ng/mL/180 min for Po). In summary, Pe insulin delivery exacerbates hypoglycemia, particularly in the presence of a diminished glucagon response. Po vein insulin delivery, or strategies that mimic it (i.e., liver-preferential insulin analogs), should therefore lessen hypoglycemia.
Assuntos
Diabetes Mellitus Tipo 1/tratamento farmacológico , Hipoglicemia/induzido quimicamente , Insulina/administração & dosagem , Insulina/efeitos adversos , Administração Intravenosa , Animais , Glicemia/metabolismo , Cães , Glucagon/farmacologia , Glucose/metabolismo , Humanos , Insulina/uso terapêutico , Masculino , Veia Porta , Somatostatina/farmacologiaRESUMO
Dogs consuming a hypercaloric high-fat and -fructose diet (52 and 17% of total energy, respectively) or a diet high in either fructose or fat for 4 wk exhibited blunted net hepatic glucose uptake (NHGU) and glycogen deposition in response to hyperinsulinemia, hyperglycemia, and portal glucose delivery. The effect of a hypercaloric diet containing neither fructose nor excessive fat has not been examined. Dogs with an initial weight of ≈25 kg consumed a chow and meat diet (31% protein, 44% carbohydrate, and 26% fat) in weight-maintaining (CTR; n = 6) or excessive (Hkcal; n = 7) amounts for 4 wk (cumulative weight gain 0.0 ± 0.3 and 1.5 ± 0.5 kg, respectively, P < 0.05). They then underwent clamp studies with infusions of somatostatin and intraportal insulin (4× basal) and glucagon (basal). The hepatic glucose load was doubled with peripheral (Pe) glucose infusion for 90 min (P1) and intraportal glucose at 4 mg·kg(-1)·min(-1) plus Pe glucose for the final 90 min (P2). NHGU was blunted (P < 0.05) in Hkcal during both periods (mg·kg(-1)·min(-1); P1: 1.7 ± 0.2 vs. 0.3 ± 0.4; P2: 3.6 ± 0.3 vs. 2.3 ± 0.4, CTR vs. Hkcal, respectively). Terminal hepatic glucokinase catalytic activity was reduced nearly 50% in Hkcal vs. CTR (P < 0.05), although glucokinase protein did not differ between groups. In Hkcal vs. CTR, liver glycogen was reduced 27% (P < 0.05), with a 91% increase in glycogen phosphorylase activity (P < 0.05) but no significant difference in glycogen synthase activity. Thus, Hkcal impaired NHGU and glycogen synthesis compared with CTR, indicating that excessive energy intake, even if the diet is balanced and nutritious, negatively impacts hepatic glucose metabolism.
Assuntos
Glucose/farmacocinética , Hiperfagia/metabolismo , Fígado/metabolismo , Animais , Glicemia/metabolismo , Peptídeo C/sangue , Doença Crônica , Cães , Ingestão de Alimentos , Técnica Clamp de Glucose , Insulina/metabolismo , Masculino , Aumento de PesoRESUMO
In dogs consuming a high-fat and -fructose diet (52 and 17% of total energy, respectively) for 4 wk, hepatic glucose uptake (HGU) in response to hyperinsulinemia, hyperglycemia, and portal glucose delivery is markedly blunted with reduction in glucokinase (GK) protein and glycogen synthase (GS) activity. The present study compared the impact of selective increases in dietary fat and fructose on liver glucose metabolism. Dogs consumed weight-maintaining chow (CTR) or hypercaloric high-fat (HFA) or high-fructose (HFR) diets diet for 4 wk before undergoing clamp studies with infusion of somatostatin and intraportal insulin (3-4 times basal) and glucagon (basal). The hepatic glucose load (HGL) was doubled during the clamp using peripheral vein (Pe) glucose infusion in the first 90 min (P1) and portal vein (4 mg·kg(-1)·min(-1)) plus Pe glucose infusion during the final 90 min (P2). During P2, HGU was 2.8 ± 0.2, 1.0 ± 0.2, and 0.8 ± 0.2 mg·kg(-1)·min(-1) in CTR, HFA, and HFR, respectively (P < 0.05 for HFA and HFR vs. CTR). Compared with CTR, hepatic GK protein and catalytic activity were reduced (P < 0.05) 35 and 56%, respectively, in HFA, and 53 and 74%, respectively, in HFR. Liver glycogen concentrations were 20 and 38% lower in HFA and HFR than CTR (P < 0.05). Hepatic Akt phosphorylation was decreased (P < 0.05) in HFA (21%) but not HFR. Thus, HFR impaired hepatic GK and glycogen more than HFA, whereas HFA reduced insulin signaling more than HFR. HFA and HFR effects were not additive, suggesting that they act via the same mechanism or their effects converge at a saturable step.
Assuntos
Dieta Hiperlipídica , Gorduras na Dieta/farmacologia , Frutose/farmacologia , Glucose/metabolismo , Fígado/efeitos dos fármacos , Fígado/metabolismo , Animais , Glicemia/metabolismo , Dieta Hiperlipídica/veterinária , Carboidratos da Dieta/farmacologia , Cães , Glucoquinase/metabolismo , Glicerol/metabolismo , Ácido Láctico/metabolismo , Masculino , Triglicerídeos/metabolismoRESUMO
The impact of the novel basal insulin LY2605541 (LY) on hepatic and nonhepatic glucose uptake (non-HGU) was evaluated. Conscious dogs underwent euglycemic clamps with tracer and hepatic balance measurements. Clamp period infusions were peripheral venous regular insulin (0.1 nmol â kg(-1) â h(-1) [control], n = 6) or LY (bolus [nmol/kg], continuous [nmol â kg(-1) â h(-1)]: 0.5, 0.5 [n = 6]; 0.375, 0.375 [n = 5]; 0.25, 0.25 [n = 4]), somatostatin, and glucose, as well as intraportal glucagon (basal). During the clamp, the dogs switched from net hepatic glucose output to uptake (rates reached 2.1 ± 1.2, 0.9 ± 2.1, 8.6 ± 2.3, and 6.0 ± 1.1 µmol â kg(-1) â min(-1) within 5 h in control, LY0.25, LY0.375, and LY0.5, respectively). Non-HGU in LY increased less than in control; the ratio of change from basal in non-HGU to change in net hepatic glucose balance, calculated when glucose infusion rates (GIRs) were ~20 µmol â kg(-1) â min(-1) in all groups, was higher in control (1.17 ± 0.38) versus LY0.25 (0.39 ± 0.33), LY0.375 (-0.01 ± 0.13), and LY0.5 (-0.09 ± 0.07). Likewise, the change from baseline in glucose Rd-to-Ra ratio was greatest in control (1.4 ± 0.3 vs. 0.6 ± 0.4, 0.5 ± 0.2, and 0.6 ± 0.2 in LY0.25, LY0.375, and LY0.5, respectively). In contrast to exogenously administered human insulin, LY demonstrated preferential hepatic effects, similar to endogenously secreted insulin. Therefore, the analog might reduce complications associated with current insulin therapy.
Assuntos
Glucose/metabolismo , Hipoglicemiantes/farmacologia , Insulina Lispro/farmacologia , Insulinas/farmacologia , Fígado/efeitos dos fármacos , Fígado/metabolismo , Polietilenoglicóis/farmacologia , Animais , Glicemia/metabolismo , Cães , Humanos , Ácido LácticoRESUMO
The impact of the GLP-1 receptor agonist lixisenatide on postprandial glucose disposition was examined in conscious dogs to identify mechanisms for its improvement of meal tolerance in humans and examine the tissue disposition of meal-derived carbohydrate. Catheterization for measurement of hepatic balance occurred ≈16 days before study. After being fasted overnight, dogs received a subcutaneous injection of 1.5 µg/kg lixisenatide or vehicle (saline, control; n = 6/group). Thirty minutes later, they received an oral meal feeding (93.4 kJ; 19% protein, 71% glucose polymers, and 10% lipid). Acetaminophen was included in the meal in four control and five lixisenatide dogs for assessment of gastric emptying. Observations continued for 510 min; absorption was incomplete in lixisenatide at that point. The plasma acetaminophen area under the curve (AUC) in lixisenatide was 65% of that in control (P < 0.05). Absorption of the meal began within 15 min in control but was delayed until ≈30-45 min in lixisenatide. Lixisenatide reduced (P < 0.05) the postprandial arterial glucose AUC ≈54% and insulin AUC ≈44%. Net hepatic glucose uptake did not differ significantly between groups. Nonhepatic glucose uptake tended to be reduced by lixisenatide (6,151 ± 4,321 and 10,541 ± 1,854 µmol·kg(-1)·510 min(-1) in lixisenatide and control, respectively; P = 0.09), but adjusted (for glucose and insulin concentrations) values did not differ (18.9 ± 3.8 and 19.6 ± 7.9 l·kg(-1)·pmol(-1)·l(-1), lixisenatide and control, respectively; P = 0.94). Thus, lixisenatide delays gastric emptying, allowing more efficient disposal of the carbohydrate in the feeding without increasing liver glucose disposal. Lixisenatide could prove to be a valuable adjunct in treatment of postprandial hyperglycemia in impaired glucose tolerance or type 2 diabetes.
Assuntos
Glucose/metabolismo , Hipoglicemiantes/farmacologia , Fígado/efeitos dos fármacos , Fígado/metabolismo , Peptídeos/farmacologia , Período Pós-Prandial/efeitos dos fármacos , Acetaminofen/administração & dosagem , Animais , Estado de Consciência , Cães , Feminino , Esvaziamento Gástrico/efeitos dos fármacos , Glucagon/sangue , Receptor do Peptídeo Semelhante ao Glucagon 1 , Insulina/sangue , Masculino , Receptores de Glucagon/agonistasRESUMO
The importance of hypothalamic insulin action to the regulation of hepatic glucose metabolism in the presence of a normal liver/brain insulin ratio (3:1) is unknown. Thus, we assessed the role of central insulin action in the response of the liver to normal physiologic hyperinsulinemia over 4 h. Using a pancreatic clamp, hepatic portal vein insulin delivery was increased three- or eightfold in the conscious dog. Insulin action was studied in the presence or absence of intracerebroventricularly mediated blockade of hypothalamic insulin action. Euglycemia was maintained, and glucagon was clamped at basal. Both the molecular and metabolic aspects of insulin action were assessed. Blockade of hypothalamic insulin signaling did not alter the insulin-mediated suppression of hepatic gluconeogenic gene transcription but blunted the induction of glucokinase gene transcription and completely blocked the inhibition of glycogen synthase kinase-3ß gene transcription. Thus, central and peripheral insulin action combined to control some, but not other, hepatic enzyme programs. Nevertheless, inhibition of hypothalamic insulin action did not alter the effects of the hormone on hepatic glucose flux (production or uptake). These data indicate that brain insulin action is not a determinant of the rapid (<4 h) inhibition of hepatic glucose metabolism caused by normal physiologic hyperinsulinemia in this large animal model.
Assuntos
Encéfalo/fisiologia , Glucose/metabolismo , Insulina/fisiologia , Fígado/metabolismo , Animais , Cães , Feminino , Glucoquinase/fisiologia , Quinase 3 da Glicogênio Sintase/metabolismo , Glicogênio Sintase Quinase 3 beta , Glicogenólise , Hipotálamo/fisiologia , Masculino , Fosforilação , Fator de Transcrição STAT3/metabolismoRESUMO
The cellular events mediating the pleiotropic actions of portal vein glucose (PoG) delivery on hepatic glucose disposition have not been clearly defined. Likewise, the molecular defects associated with postprandial hyperglycemia and impaired hepatic glucose uptake (HGU) following consumption of a high-fat, high-fructose diet (HFFD) are unknown. Our goal was to identify hepatocellular changes elicited by hyperinsulinemia, hyperglycemia, and PoG signaling in normal chow-fed (CTR) and HFFD-fed dogs. In CTR dogs, we demonstrated that PoG infusion in the presence of hyperinsulinemia and hyperglycemia triggered an increase in the activity of hepatic glucokinase (GK) and glycogen synthase (GS), which occurred in association with further augmentation in HGU and glycogen synthesis (GSYN) in vivo. In contrast, 4 weeks of HFFD feeding markedly reduced GK protein content and impaired the activation of GS in association with diminished HGU and GSYN in vivo. Furthermore, the enzymatic changes associated with PoG sensing in chow-fed animals were abolished in HFFD-fed animals, consistent with loss of the stimulatory effects of PoG delivery. These data reveal new insight into the molecular physiology of the portal glucose signaling mechanism under normal conditions and to the pathophysiology of aberrant postprandial hepatic glucose disposition evident under a diet-induced glucose-intolerant condition.
Assuntos
Dieta Hiperlipídica/efeitos adversos , Frutose/efeitos adversos , Glucose/metabolismo , Fígado/metabolismo , Veia Porta/fisiologia , Animais , Cães , Frutose/administração & dosagem , Glucoquinase/análise , Glucoquinase/metabolismo , Glucose/administração & dosagem , Intolerância à Glucose/etiologia , Glicogênio Sintase/metabolismo , Hiperglicemia/etiologia , Hiperglicemia/metabolismo , Hiperinsulinismo/etiologia , Fígado/enzimologia , Glicogênio Hepático/biossíntese , Masculino , Transdução de Sinais/fisiologiaRESUMO
Net hepatic glucose uptake (NHGU) is an important contributor to postprandial glycemic control. We hypothesized that NHGU is reduced during normal pregnancy and in a pregnant diet-induced model of impaired glucose intolerance/gestational diabetes mellitus (IGT/GDM). Dogs (n = 7 per group) that were nonpregnant (N), normal pregnant (P), or pregnant with IGT/GDM (pregnant dogs fed a high-fat and -fructose diet [P-HFF]) underwent a hyperinsulinemic-hyperglycemic clamp with intraportal glucose infusion. Clamp period insulin, glucagon, and glucose concentrations and hepatic glucose loads did not differ among groups. The N dogs reached near-maximal NHGU rates within 30 min; mean ± SEM NHGU was 105 ± 9 µmol·100 g liver⻹·min⻹. The P and P-HFF dogs reached maximal NHGU in 90-120 min; their NHGU was blunted (68 ± 9 and 16 ± 17 µmol·100 g liver⻹·min⻹, respectively). Hepatic glycogen synthesis was reduced 20% in P versus N and 40% in P-HFF versus P dogs. This was associated with a reduction (>70%) in glycogen synthase activity in P-HFF versus P and increased glycogen phosphorylase (GP) activity in both P (1.7-fold greater than N) and P-HFF (1.8-fold greater than P) dogs. Thus, NHGU under conditions mimicking the postprandial state is delayed and suppressed in normal pregnancy, with concomitant reduction in glycogen storage. NHGU is further blunted in IGT/GDM. This likely contributes to postprandial hyperglycemia during pregnancy, with potential adverse outcomes for the fetus and mother.
Assuntos
Diabetes Gestacional/metabolismo , Modelos Animais de Doenças , Regulação para Baixo , Intolerância à Glucose/metabolismo , Resistência à Insulina , Glicogênio Hepático , Fígado/metabolismo , Animais , Diabetes Gestacional/sangue , Diabetes Gestacional/fisiopatologia , Dieta Hiperlipídica/efeitos adversos , Cães , Feminino , Frutose/efeitos adversos , Glucoquinase/metabolismo , Glucose/metabolismo , Intolerância à Glucose/sangue , Intolerância à Glucose/fisiopatologia , Glicogênio Fosforilase Hepática/metabolismo , Glicogênio Sintase/metabolismo , Hiperglicemia/etiologia , Fígado/enzimologia , Fenômenos Fisiológicos da Nutrição Materna , Período Pós-Prandial , GravidezRESUMO
Studies were carried out on conscious female non-pregnant (NP) and pregnant (P; third-trimester) dogs (n 16; eight animals per group) to define the role of the liver in mixed meal disposition with arteriovenous difference and tracer techniques. Hepatic and hindlimb substrate disposal was assessed for 390 min during and after an intragastric mixed meal infusion labelled with [¹4C]glucose. The P dogs exhibited postprandial hyperglycaemia compared with NP dogs (area under the curve (AUC; change from basal over 390 min) of arterial plasma glucose: 86 680 (sem 12 140) and 187 990 (sem 33 990) mg/l in NP and P dogs, respectively; P < 0·05). Plasma insulin concentrations did not differ significantly between the groups (AUC: 88 230 (sem 16 314) and 69 750 (sem 19 512) pmol/l in NP and P dogs, respectively). Net hepatic glucose uptake totalled 3691 (sem 508) v. 5081 (sem 1145) mg/100 g liver in NP and P dogs, respectively (P = 0·38). The AUC of glucose oxidation by the gut and hindlimb were not different in NP and P dogs, but hepatic glucose oxidation (84 (sem 13) v. 206 (sem 30) mg/100 g liver) and glycogen synthesis (0·4 (sem 0·5) v. 26 (sem 0·7) g/100 g liver) were greater in P dogs (P < 0·05). The proportion of hepatic glycogen deposited via the direct pathway did not differ between the groups. Hindlimb glucose uptake and skeletal muscle glycogen synthesis was similar between the groups, although final glycogen concentrations were higher in NP dogs (9·6 (sem 0·6) v. 70 (sem 0·6) mg/g muscle; P < 0·05). Thus, hepatic glucose oxidation and glycogen storage were augmented in late pregnancy. Enhanced hepatic glycogen storage following a meal probably facilitates the maintenance of an adequate glucose supply to maternal and fetal tissues during the post-absorptive period.