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      Liver blood dynamics after bariatric surgery: the effects of mixed-meal test and incretin infusions

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          Abstract

          Aims/hypothesis

          The mechanisms for improved glycemic control after bariatric surgery in subjects with type 2 diabetes (T2D) are not fully known. We hypothesized that dynamic hepatic blood responses to a mixed-meal are changed after bariatric surgery in parallel with an improvement in glucose tolerance.

          Methods

          A total of ten morbidly obese subjects with T2D were recruited to receive a mixed-meal and a glucose-dependent insulinotropic polypeptide (GIP) infusion before and early after (within a median of less than three months) bariatric surgery, and hepatic blood flow and volume (HBV) were measured repeatedly with combined positron emission tomography/MRI. Ten lean non-diabetic individuals served as controls.

          Results

          Bariatric surgery leads to a significant decrease in weight, accompanied with an improved β-cell function and glucagon-like peptide 1 (GLP-1) secretion, and a reduction in liver volume. Blood flow in portal vein (PV) was increased by 1.65-fold ( P = 0.026) in response to a mixed-meal in subjects after surgery, while HBV decreased in all groups ( P < 0.001). When the effect of GIP infusion was tested separately, no change in hepatic arterial and PV flow was observed, but HBV decreased as seen during the mixed-meal test.

          Conclusions/interpretation

          Early after bariatric surgery, PV flow response to a mixed-meal is augmented, improving digestion and nutrient absorption. GIP influences the post-prandial reduction in HBV thereby diverting blood to the extrahepatic sites.

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          Most cited references26

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          Cardioprotective and vasodilatory actions of glucagon-like peptide 1 receptor are mediated through both glucagon-like peptide 1 receptor-dependent and -independent pathways.

          The glucagon-like peptide 1 receptor (GLP-1R) is believed to mediate glucoregulatory and cardiovascular effects of the incretin hormone GLP-1(7-36) (GLP-1), which is rapidly degraded by dipeptidyl peptidase-4 (DPP-4) to GLP-1(9-36), a truncated metabolite generally thought to be inactive. Novel drugs for the treatment of diabetes include analogues of GLP-1 and inhibitors of DPP-4; however, the cardiovascular effects of distinct GLP-1 peptides have received limited attention. Here, we show that endothelium and cardiac and vascular myocytes express a functional GLP-1R as GLP-1 administration increased glucose uptake, cAMP and cGMP release, left ventricular developed pressure, and coronary flow in isolated mouse hearts. GLP-1 also increased functional recovery and cardiomyocyte viability after ischemia-reperfusion injury of isolated hearts and dilated preconstricted arteries from wild-type mice. Unexpectedly, many of these actions of GLP-1 were preserved in Glp1r(-/-) mice. Furthermore, GLP-1(9-36) administration during reperfusion reduced ischemic damage after ischemia-reperfusion and increased cGMP release, vasodilatation, and coronary flow in wild-type and Glp1r(-/-) mice, with modest effects on glucose uptake. Studies using a DPP-4-resistant GLP-1R agonist and inhibitors of DPP-4 and nitric oxide synthase showed that the effects of GLP-1(7-36) were partly mediated by GLP-1(9-36) through a nitric oxide synthase-requiring mechanism that is independent of the known GLP-1R. These data describe cardioprotective actions of GLP-1(7-36) mediated through the known GLP-1R and novel cardiac and vascular actions of GLP-1(7-36) and its metabolite GLP-1(9-36) independent of the known GLP-1R. Our data suggest that the extent to which GLP-1 is metabolized to GLP-1(9-36) may have functional implications in the cardiovascular system.
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            Fat accumulation in the liver is associated with defects in insulin suppression of glucose production and serum free fatty acids independent of obesity in normal men.

            We determined whether interindividual variation in hepatic insulin sensitivity could be attributed to variation in liver fat content (LFAT) independent of obesity. We recruited 30 healthy nondiabetic men whose LFAT (determined by proton spectroscopy); intraabdominal, sc, and total (determined by magnetic resonance imaging) fat; and insulin sensitivity of endogenous glucose rate of production (R(a)) and suppression of serum FFA [euglycemic insulin clamp combined with [3-(3)H]glucose (0-300 min); insulin infusion rate, 0.3 mU/kg.min, 120-300 min] were measured. The men were divided into groups of low (mean +/- SD, 1.7 +/- 0.2%) and high (10.5 +/- 2.0%) LFAT based on their median fat content. The low and high LFAT groups were comparable with respect to age (44 +/- 2 vs. 42 +/- 2 yr), body mass index (25 +/- 1 vs. 26 +/- 1 kg/m(2) ), waist to hip ratio (0.953 +/- 0.013 vs. 0.953 +/- 0.013), maximal oxygen uptake (35.6 +/- 1.5 vs. 33.5 +/- 1.5 ml/kg.min), and intraabdominal, sc, and total fat. The high compared with the low LFAT group had several features of insulin resistance, including fasting hyperinsulinemia (7.3 +/- 0.6 vs. 5.3 +/- 0.6 mU/liter; P < 0.02, high vs. low LFAT) hypertriglyceridemia (1.4 +/- 0.2 vs. 0.9 +/- 0.1 mmol/liter; P < 0.02), a low high density lipoprotein (HDL) cholesterol concentration (1.4 +/- 0.1 vs. 1.6 +/- 0.1 mmol/liter; P < 0.05), and a higher ambulatory 24-h systolic blood pressure (130 +/- 3 vs. 122 +/- 3 mm Hg; P < 0.05). Basal glucose R(a) and serum FFA were comparable between the groups, whereas insulin suppression of glucose R(a) [51 +/- 8 vs. 20 +/- 12 mg/m(2).min during 240-300 min (P < 0.05) or -55 +/- 7 vs. -85 +/- 12% below basal (P < 0.05, high vs. low LFAT)] and of serum FFA (299 +/- 33 vs. 212 +/- 13 micromol/liter; 240-300 min; P < 0.02) were impaired in the high compared with the low LFAT group. Insulin stimulation of glucose Rd were comparable in the men with high LFAT (141 +/- 12 mg/m(2).min) and those with low LFAT (156 +/- 14 mg/m(2).min; P = NS). Fat accumulation in the liver is, independent of body mass index and intraabdominal and overall obesity, characterized by several features of insulin resistance in normal weight and moderately overweight subjects.
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              A model-based method for assessing insulin sensitivity from the oral glucose tolerance test.

              Available insulin sensitivity (IS) methods based on the oral glucose tolerance test (OGTT) are empirical. We used a glucose-insulin model to derive an OGTT-based IS (oral glucose insulin sensitivity [OGIS]) index, which predicts glucose clearance in a glucose clamp. We validated OGIS against clamp data. OGIS requires glucose and insulin concentrations from a 75-g OGTT at 0, 2, and 3 h (3-h OGTT) or at 0, 1.5, and 2 h (2-h OGTT). The formula includes six constants optimized to match the clamp results. For this purpose, 15 lean nondiabetic subjects (BMI 25 kg/m2), and 38 subjects with type 2 diabetes randomly underwent an OGTT and a 120 mU x min(-1) x m(-2) insulin infusion euglycemic clamp. Glucose clearance (Cl CLAMP), calculated as the ratio of glucose infusion to concentration during the last hour of the clamp, was compared with OGIS. OGIS was also tested on an independent group of 13 subjects with impaired glucose tolerance (IGT). OGIS and Cl CLAMP were correlated in the whole group (R = 0.77, P < 0.0001), in the subgroups (lean: R = 0.59; obese: R = 0.73; type 2 diabetes: R = 0.49; P < 0.02), and in the independent IGT group (R = 0.65, P < 0.02). Reproducibility of OGIS and Cl CLAMP were similar (coefficients of variation: OGIS 7.1%, Cl CLAMP 6.4%). OGIS was as effective as Cl CLAMP in discriminating between groups (for OGIS, lean vs. obese: 440 +/- 16 vs. 362 +/- 11 ml x min(-1) x m(-2), p < 0.001; lean vs. type 2 diabetes: 440 +/- 16 vs. 239 +/- 7, P < 0.0001; obese vs. type 2 diabetes: 362 +/- 11 vs. 239 +/- 7, P < 0.0001; results were similar for Cl CLAMP). The relationships between IS and BMI, fasting plasma insulin, and insulin secretion (calculated from the OGTT insulin concentration) were examined. OGIS yielded results similar to Cl CLAMP and fully consistent with established physiological principles. The performance of the index for the 3-h and 2-h OGTT was similar. OGIS is an index of IS in good agreement with the clamp. Because of its simplicity (only three blood samples required), this method has potential use for clinical investigation including large-scale epidemiological studies.

                Author and article information

                Journal
                Endocr Connect
                Endocr Connect
                EC
                Endocrine Connections
                Bioscientifica Ltd (Bristol )
                2049-3614
                July 2018
                25 June 2018
                : 7
                : 7
                : 888-896
                Affiliations
                [1 ]Turku PET Centre University of Turku, Turku, Finland
                [2 ]Department of Gastroenterology Turku University Hospital, Turku, Finland
                [3 ]Division of Digestive Surgery and Urology Turku University Hospital, Turku, Finland
                [4 ]Faculty of Medicine Kagawa University, Kagawa, Japan
                [5 ]Department of Biostatistics University of Turku, Turku, Finland
                [6 ]Institute of Neuroscience National Research Council, Padua, Italy
                [7 ]Department of Clinical Sciences Lund University Diabetes Centre, Malmö, Sweden
                [8 ]Department of Radiology University of Turku and Turku University Hospital, Turku, Finland
                [9 ]Department of Endocrinology Turku University Hospital, Turku, Finland
                Author notes
                Correspondence should be addressed to P Nuutila: pirjo.nuutila@ 123456utu.fi

                *(H Honka and J Koffert contributed equally to this work)

                Article
                EC180234
                10.1530/EC-18-0234
                6063878
                29941634
                8f33650d-140e-4ae0-9aa0-029ad514bc49
                © 2018 The authors

                This work is licensed under a Creative Commons Attribution 4.0 International License.

                History
                : 19 June 2018
                : 25 June 2018
                Categories
                Research

                portal vein blood flow,hepatic blood volume,glucose-dependent insulinotropic polypeptide,bariatric surgery,positron emission tomography

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