Enhanced interleukin-6 in human adipose tissue vein after sprint exercise: Results from a pilot study.

BACKGROUND: Low-volume sprint exercise is likely to reduce body fat. Interleukin (IL-6) may mediate this by increasing adipose tissue (AT) lipolysis. Therefore, the exchange of AT IL-6 and glycerol, a marker of lipolysis, was examined in 10 healthy subjects performing three 30-s all-out sprints. METHODS: Blood samples were obtained from brachial artery (a) and a superficial subcutaneous vein (v) on the anterior abdominal wall up to 9 min after the last sprint and analysed for IL-6 and glycerol. RESULTS: Arterial IL-6 increased 2-fold from rest to last sprint. AT venous IL-6 increased 15-fold from 0.4 ± 0.4 at rest to 7.0 ± 4 pg × mL-1 (p < 0.0001) and AT v-a difference increased 45-fold from 0.12 ± 0.3 to 6.0 ± 5 pg x mL-1 (p < 0.0001) 9 min after last sprint. Arterial glycerol increased 2.5-fold from rest to 9 min postsprint 1 (p < 0.0001) and was maintained during the exercise period. AT venous and v-a difference of glycerol increased 2-fold from rest to 9 min postsprint 1 (p < 0.0001 and p = 0.01, respectively), decreased until 18 min postsprint 2 (p < 0.001 and p < 0.0001), and then increased again until 9 min after last sprint (both p < 0.01). CONCLUSIONS: The concurrent increase in venous IL-6 and glycerol in AT after last sprint is consistent with an IL-6 induced lipolysis in AT. Glycerol data also indicated an initial increase in lipolysis after sprint 1 that was unrelated to IL-6. Increased IL-6 in adipose tissue may, therefore, complement other sprint exercise-induced lipolytic agents.

Age- and sex-specific changes in visceral fat mass throughout the life-span.

OBJECTIVE: Visceral fat mass (VFM) is a risk factor for cardiovascular diseases, type 2 diabetes mellitus, and malignancy; however, normative data are limited. The aim of this study was to provide reference data for VFM from a large, apparently healthy Caucasian adult population. METHODS: Volunteers aged 20 to 93 years from the Copenhagen City Heart Study had a standardized whole-body dual-energy x-ray absorptiometry scan performed using the iDXA (GE Lunar). Total and regional fat mass was measured. VFM was quantified using the CoreScan application. RESULTS: A total of 1277 participants were included (708 women, mean [SD], age: 56 [19] years, height: 1.66 [0.07] m, BMI: 24.64 [4.31] kg/m2 ; and 569 men, age: 57 [18] years, height: 1.80 [0.07] m, BMI: 25.99 [3.86] kg/m2 ). Increased VFM was positively correlated with age in both sexes. Men had significantly higher VFM in mass (g) after normalization to body size (m2 ) and total fat mass (p < 0.001). VFM increased more in women with high values of the android/gynoid ratio. CONCLUSIONS: Normative data of VFM from a large, healthy Danish cohort aged 20 to 93 years are presented. VFM increased with age in both sexes, but men had significantly higher VFM compared with women with the same BMI, body fat percentage, and fat mass index.

Postprandial muscle protein synthesis rate is unaffected by 20-day habituation to a high protein intake: a randomized controlled, crossover trial.

PURPOSE: During the last decade more researchers have argued in favor of an increased protein intake for older adults. However, there is a lack of knowledge on the long-term effects of conforming to such a high protein intake with regards to the basal and postprandial muscle protein turnover. The purpose of this study was to compare the postprandial synthesis response in muscle proteins, and the abundance of directly incorporated food-derived amino acids following habituation to high vs. recommended level of protein intake. METHODS: In a double blinded crossover intervention 11 older male participants (66.6 ± 1.7 years of age) were habituated for 20 days to a recommended protein (RP) intake (1.1 g protein/kg lean body mass (LBM)/day) and a high protein (HP) intake (> 2.1 g protein/kg LBM/day). Following each habituation period, intrinsically labelled proteins were ingested as part of a mixed meal to determine the incorporation of meal protein-derived amino acids into myofibrillar proteins. Furthermore, the myofibrillar fractional synthesis rate (FSR) and amino acid kinetics across the leg were determined using gold standard stable isotope tracer methodologies. RT qPCR was used to assess the expression of markers related to muscle proteinsynthesis and breakdown. RESULTS: No impact of habituation was observed on skeletal muscle amino acid or protein kinetics. However, the shunting of amino acids directly from artery to vein was on average 2.9 [Formula: see text]mol/min higher following habituation to HP compared to RP. CONCLUSIONS: In older males, habituation to a higher than the currently recommended protein intake did not demonstrate any adaptions in the muscle protein turnover or markers hereof when subjected to an intake of an identical mixed meal. CLINICAL TRIAL REGISTRY: Journal number NCT02587156, Clinicaltrials.org. Date of registration: October 27th, 2015.

The Renal Extraction and the Natriuretic Action of GLP-1 in Humans Depend on Interaction With the GLP-1 Receptor.

PURPOSE: The natriuretic effect of glucagon-like peptide-1 (GLP-1) in humans is independent of changes in renal plasma flow (RPF) and glomerular filtration rate (GFR) but may involve suppression of angiotensin II (ANG II) and a significant (~45%) renal extraction of GLP-1. The current study was designed to investigate the consequences for the renal extraction and the natriuretic effect of blocking GLP-1 receptors with the specific GLP-1 receptor antagonist, Exendin 9-39 (Ex 9-39). METHODS: Under fixed sodium intake for 4 days before each study day, 6 healthy male participants were recruited from our recent study where GLP-1 or vehicle was infused (1). In the present new experiments, participants were examined during a 3-hour infusion of GLP-1 (1.5 pmol/kg/min) together with a 3.5-hour infusion of Ex 9-39 (900 pmol/kg/min). Timed urine collections were conducted throughout the experiments. Renal extraction of GLP-1 as well as RPF and GFR were measured via Fick's principle after catheterization of a renal vein. Arterial plasma renin, ANG II, and aldosterone concentrations were measured. RESULTS: Co-infusion of Ex 9-39 significantly reduced renal extraction of GLP-1 to ~25% compared with GLP-1 infusion alone (~45%). Urinary sodium excretions remained at baseline levels during co-infusion of Ex 9-39 as well as vehicle. By contrast, GLP-1 infusion alone resulted in a 2-fold increase in natriuresis. Ex 9-39 abolished the GLP-1-induced decrease in arterial ANG II concentrations. RPF and GFR remained unchanged during all experiments. CONCLUSIONS: Renal extraction of GLP-1 and its effect on natriuresis are both dependent on GLP-1 receptor activation in healthy humans.

Increased oral sodium chloride intake in humans amplifies selectively postprandial GLP-1 but not GIP, CCK, and gastrin in plasma.

Human studies have demonstrated that physiologically relevant changes in circulating glucagon-like peptide-1 (GLP-1) elicit a rapid increase in renal sodium excretion when combined with expansion of the extracellular fluid volume. Other studies support the involvement of various gastrointestinal hormones, e.g., gastrin and cholecystokinin (CCK) in a gut-kidney axis, responsible for a rapid-acting feed-forward natriuretic mechanism. This study was designed to investigate the hypothesis that the postprandial GLP-1 plasma concentration is sensitive to the sodium content in the meal. Under fixed sodium intake for 4 days prior to each experimental day, 10 lean healthy male participants were examined twice in random order after a 12-hr fasting period. Arterial blood samples were collected at 10-20-min intervals for 140 min after 75 grams of oral glucose + 6 grams of oral sodium chloride (NaCl) load versus 75 grams of glucose alone. Twenty-four-hour baseline urinary sodium excretions were similar between study days. Arterial GLP-1 levels increased during both oral glucose loads and were significantly higher at the 40-80 min period during glucose + NaCl compared to glucose alone. The postprandial arterial responses of CCK, gastrin, and glucose-dependent insulinotropic polypeptide as well as glucose, insulin, and C-peptide did not differ between the two study days. Arterial renin, aldosterone, and natriuretic peptides levels did not change within subjects or between study days. Angiotensin II levels were significantly lower at the time GLP-1 was higher (60-80 min) during glucose + NaCl. Sodium intake in addition to a glucose load selectively amplifies the postprandial GLP-1 plasma concentration. Thus, GLP-1 may be part of an acute feed-forward mechanism for natriuresis.

Impact of habituated dietary protein intake on fasting and postprandial whole-body protein turnover and splanchnic amino acid metabolism in elderly men: a randomized, controlled, crossover trial.

BACKGROUND: Efficacy of protein absorption and subsequent amino acid utilization may be reduced in the elderly. Higher protein intakes have been suggested to counteract this. OBJECTIVES: We aimed to elucidate how habituated amounts of protein intake affect the fasted state of, and the stimulatory effect of a protein-rich meal on, protein absorption, whole-body protein turnover, and splanchnic amino acid metabolism. METHODS: Twelve men (65-70 y) were included in a double-blinded crossover intervention study, consisting of a 20-d habituation period to a protein intake at the RDA or a high amount [1.1 g · kg lean body mass (LBM)-1 · d-1 or >2.1 g · kg LBM-1 · d-1, respectively], each followed by an experimental trial with a primed, constant infusion of D8-phenylalanine and D2-tyrosine. Arterial and hepatic venous blood samples were obtained after an overnight fast and repeatedly 4 h after a standardized meal including intrinsically labeled whey protein concentrate and calcium-caseinate proteins. Blood was analyzed for amino acid concentrations and phenylalanine and tyrosine tracer enrichments from which whole-body and splanchnic amino acid and protein kinetics were calculated. RESULTS: High (compared with the recommended amount of) protein intake resulted in a higher fasting whole-body protein turnover with a resultant mean ± SEM 0.03 ± 0.01 µmol · kg LBM-1 · min-1 lower net balance (P < 0.05), which was not rescued by the intake of a protein-dense meal. The mean ± SEM plasma protein fractional synthesis rate was 0.13 ± 0.06%/h lower (P < 0.05) after habituation to high protein. Furthermore, higher fasting and postprandial amino acid removal were observed after habituation to high protein, yielding higher urea excretion and increased phenylalanine oxidation rates (P < 0.01). CONCLUSIONS: Three weeks of habituation to high protein intake (>2.1 g protein · kg LBM-1 · d-1) led to a significantly higher net protein loss in the fasted state. This was not compensated for in the 4-h postprandial period after intake of a meal high in protein.This trial was registered at clinicaltrials.gov as NCT02587156.

Lymphatic drainage affects lipolytic activity of femoral adipose tissue in women.

It has been shown that many molecules released by adipose tissue (AT) into interstitial fluid can reach the bloodstream preferentially via lymphatic system. Worsened lymphatic drainage may alter interstitial fluid (ISF) composition and thus affect microenvironment of adipocytes. Nevertheless, the effect of lymphatic drainage on AT functions remains unknown. Therefore, we analyzed the lipolytic activity of femoral AT in two groups of premenopausal women similar in adiposity but differing in the efficiency of lymphatic drainage of lower body as assessed by lymphoscintigraphy. Levels of lipolytic markers were assessed in plasma and ISF collected by skin blister technique in femoral area. In addition, microdialysis was used to monitor lipolysis of AT in vivo. Our results indicate that worsened lymphatic drainage is associated with lower in vivo lipolytic index and reduced lipolytic responsiveness of femoral AT to adrenergic stimuli. Thus, efficiency of lymphatic drainage appears to play a role in the regulation of AT metabolism. Accordingly, worsened lymphatic drainage could contribute to the resistance of lower body AT to intentional weigh loss.

The Copenhagen Sarcopenia Study: lean mass, strength, power, and physical function in a Danish cohort aged 20-93 years.

BACKGROUND: Despite no international consensus on the diagnostic criteria for sarcopenia, low lean mass, muscle strength, and physical function are important risk factors for disability, frailty, and mortality in older individuals, as well as in a wide range of patients with muscle loss. Here, we provide a population-based reference material of total and regional lean body mass, muscle strength/power parameters, and physical function in a healthy cohort of Danish men and women across the lifespan. METHODS: Volunteers aged 20-93 years from the Copenhagen City Heart Study were invited to establish a Danish reference material (Copenhagen Sarcopenia Study) on lean mass characteristics [appendicular lean mass (ALM), iDXA, GE Lunar], muscle function [handgrip strength (HGS), Jamar dynamometer and leg extension power (LEP), Nottingham Power Rig], and physical function [30 s sit-to-stand test (STS), 10-m maximal and habitual gait speed (GS)]. RESULTS: A total of 1305 participants [729 women (age: 56.4 ± 18.9 years, height: 1.66 ± 0.01 m, body mass index: 24.6 ± 4.3 kg/m2 and 576 men, age: 57.0 ± 17.5 years, height: 1.80 ± 0.07 m, body mass index: 26.0 ± 3.9 kg/m2 ] completed all measurements and were included in the present analysis. Lean mass characteristics (TLM, ALM, and ALM/h2 ) decreased with increasing age in both men and women (P < 0.001). Men demonstrated larger absolute and relative total ALM and higher HGS and LEP compared with women at all age intervals (P < 0.001). HGS and LEP decreased progressively with age in both men and women (P < 0.01); 30 s STS performance, habitual GS, and maximal GS decreased at an accellerated rate of decline with increasing age in both men and women (P < 0.001). Habitual GS was reduced in men and women aged ≥70 years, while maximal GS was reduced from the age of ≥60 years compared with young adults (P < 0.001). Regardless of sex, 30 s STS was reduced from the age of ≥50 years compared with the young reference group (P < 0.001) CONCLUSIONS: While the power-based measurements (LEP and 30 s STS) started to decline already at age +50 years, less power-based parameters (GS and HGS) and lean mass characteristics (TLM, ALM, and ALM/h2 ) remained unaltered until after the age of +70 years. Notably, the cut-off thresholds derived in the present study differed from earlier reference data, which underlines the importance of obtaining updated and local reference materials.

An acoustic myography functional assessment of cerebral palsy subjects compared to healthy controls during physical exercise.

Individuals with cerebral palsy (CP) participate in reduced levels of physical activity and spend an increased amount of time in a sedentary state compared with healthy control subjects. Whether this in part can be explained by impaired muscle function is still unclear. The aim of the present study was to elucidate differences in muscle fibre recruitment during treadmill exercise between CP subjects and healthy age-, sex- and BMI-matched controls. This is a case-control study. Acoustic myography (AMG), a method recording fibre use and efficiency from contracting muscles, was applied during a period of treadmill exercise. The recorded AMG parameters revealed that the CP subjects had a significantly lower initial S-score (spatial summation) than the controls (P < 0.01). However, the T-score (temporal summation) and the E-score (efficiency) showed no significant differences between individuals with CP and the healthy control subjects. The present findings indicate that CP subjects use a higher degree of spatial summation (more fibres recruited) to keep up the same speed during treadmill exercise when compared to healthy matched control subjects. Our results suggest that individuals with CP have a tendency to recruit far more muscle fibres during bouts of exercise than healthy individuals. This may partly explain why CP subjects experience premature fatigue.

GIP-induced vasodilation in human adipose tissue involves capillary recruitment.

Glucose-dependent insulinotropic polypeptide (GIP) in combination with hyperinsulinemia increase blood flow and triglyceride clearance in subcutaneous abdominal adipose tissue in lean humans. The present experiments were performed to determine whether the increase involves capillary recruitment. Eight lean healthy volunteers were studied before and after 1 h infusion of GIP or saline during a hyperglycemic-hyperinsulinemic clamp, raising plasma glucose and insulin to postprandial levels. Subcutaneous abdominal adipose tissue blood flow (ATBF) was measured by the 133Xenon clearance technique, and microvascular blood volume was determined by contrast-enhanced ultrasound imaging. During infusion of saline and the clamp, both ATBF (2.7 ± 0.5 mL/min 100 g/tissue) and microvascular blood volume remained unchanged throughout the experiments. During GIP infusion and the clamp, ATBF increased ~fourfold to 11.4 ± 1.9 mL/min 100 g/tissue, P < 0.001. Likewise, the contrast-enhanced ultrasound signal intensity, a measure of the microvascular blood volume, increased significantly 1 h after infusion of GIP and the clamp (P = 0.003), but not in the control experiments. In conclusion, the increase in ATBF during GIP infusion involves recruitment of capillaries in healthy lean subjects, which probably increases the interaction of circulating lipoproteins with lipoprotein lipase, thus promoting adipose tissue lipid uptake.

Extracellular Fluid Volume Expansion Uncovers a Natriuretic Action of GLP-1: A Functional GLP-1-Renal Axis in Man.

PURPOSE: We have previously demonstrated that glucagon-like peptide-1 (GLP-1) does not affect renal hemodynamics or function under baseline conditions in healthy participants and in patients with type 2 diabetes mellitus. However, it is possible that GLP-1 promotes natriuresis under conditions with addition of salt and water to the extracellular fluid. The current study was designed to investigate a possible GLP-1-renal axis, inducing natriuresis in healthy, volume-loaded participants. METHODS: Under fixed sodium intake, eight healthy men were examined twice in random order during a 3-hour infusion of either GLP-1 (1.5 pmol/kg/min) or vehicle together with an intravenous infusion of 0.9% NaCl. Timed urine collections were conducted throughout the experiments. Renal plasma flow (RPF), glomerular filtration rate (GFR), and uptake and release of hormones and ions were measured via Fick's principle. RESULTS: During GLP-1 infusion, urinary sodium and osmolar excretions increased significantly compared with vehicle. Plasma renin levels decreased similarly on both days, whereas angiotensin II (ANG II) levels decreased significantly only during GLP-1 infusion. RPF and GFR remained unchanged on both days. CONCLUSIONS: In volume-loaded participants, GLP-1 induces natriuresis, probably brought about via a tubular mechanism secondary to suppression of ANG II, independent of renal hemodynamics, supporting the existence of a GLP-1-renal axis.

Markers of Local Inflammation and Bone Resorption in the Acute Diabetic Charcot Foot.

OBJECTIVE: Due to the localized nature of Charcot foot, systemically altered levels of inflammation markers can be difficult to measure. The aim of this study was to investigate whether it is possible to detect an arteriovenous (A-V) flux in any locally produced inflammatory biomarkers from an acute Charcot foot by comparing local and systemic measurements. METHODS: We included patients with acute diabetic Charcot foot. Blood was sampled from the vena saphena magna on the distal part of the crus bilaterally as well as from the arteria radialis. To minimize the A-V shunting effect, the feet were externally cooled with ice water prior to resampling. RESULTS: Both before and after cooling, the A-V flux of interleukin-6 (IL-6) between the Charcot feet and the arterial level was significantly higher than the flux between the healthy feet and the arterial level (Δvaluebefore: 7.25 versus 0.41 pg/mL, resp., p = 0.008; Δvalueafter: 10.04 versus 1.68 pg/mL, resp., p = 0.032). There were no differences in the fluxes for other markers of inflammation. CONCLUSION: We have found an increased A-V flux of IL-6 in the acute diabetic Charcot foot compared to the healthy foot in the same patients.

Microvascularization is not a limiting factor for exercise in adults with cerebral palsy.

Muscle contractures are a common complication in patients with central nervous system (CNS) lesions which limit range of movement and cause joint deformities. Furthermore, it has previously been shown that muscles with contractures have a reduced number of capillaries, indicating decreased tissue vascularization. The aim of the present study was to investigate the microvascular volume (MV) at rest and after acute exercise in the muscle tissue of individuals with cerebral palsy (CP) and healthy control individuals. Contrast-enhanced ultrasound (CEUS) was used before and after 30 min of walking or running on a treadmill in 10 healthy control participants and 10 individuals with CP to detect MV of their skeletal muscle tissue. A significant increase in the MV was observed after exercise both in the adult CP group (21-53 yr) and in the control group (21-52 yr) (1.8 ± 0.8 ΔdB to 3.1 ± 0.9 ΔdB or 42.9% and 1.5 ± 0.6 ΔdB to 2.5 ± 0.9 ΔdB or 39.0%, respectively). Furthermore, a difference in the resting MV was observed between the most severe cases of CP [gross motor function classification scale (GMFCS) 3 and 4] (2.3 ± 0.5 ΔdB) and the less severe cases (GMFCS 1 and 2) (1.5 ± 0.2 ΔdB). When the CP group was walking (3.4 km/h), the lactate levels, Borg score, and heart rate matched the level of controls when they were running (9.8 km/h). In conclusion, individuals with CP become exhausted at much lower exercise intensities than healthy individuals. This is not explained by impaired microvascularization, since the MV of the individuals with CP respond normally to increased O2 demand during acute exercise. NEW & NOTEWORTHY Cerebral palsy (CP) patients were less physically active compared with typically developed individuals. This may affect the microvascularization. We observed that the CP group became exhausted at much lower exercise intensities compared with healthy individuals. However, impaired microvascularization was not the reason for the decreased physical activity as the CP group responded normally to increased O2 demand during acute exercise. These results indicate that walking may be recommended as an intervention to train and maintain skeletal muscle tissue in individuals with CP.

Long-term effects on the progress of neuropathy after diabetic Charcot foot: an 8.5-year prospective case-control study.

OBJECTIVE: Charcot foot is a severe complication to diabetes mellitus, associated with diabetic neuropathy. Any long-term effects of a Charcot foot on the progress of neuropathy are still largely unexplored. The objective was to investigate whether a previous Charcot foot had any long-term effects on the progress of neuropathy. RESULTS: An 8.5-year follow-up case-control study of 49 individuals with diabetes mellitus, 24 of whom also had Charcot foot at baseline visit in 2005-2007. Neuropathy was assessed with a questionnaire, biothesiometry, heart rate variability and venous occlusion plethysmography. Of the 49 baseline participants, 22 were able to participate in the follow-up. Twelve had passed away in the meantime. Heart rate variability was unchanged in both groups; from 9.7 to 7.2 beats/min (p = 0.053) in the Charcot group, and 14.3 to 12.6 beats/min (p = 0.762) in the control group. Somato-sensoric neuropathy showed no difference between baseline and follow-up in the Charcot group (from 39.1 to 38.5 V) (p = 0.946), but a significantly worsened sensitivity in the control group (from 25.1 to 38.9 V) (p = 0.002). In conclusion, we found that any differences in somatic or cardial autonomic neuropathy present at baseline had disappeared at follow-up after 8.5 years.

Bone mineral density and markers of bone turnover and inflammation in diabetes patients with or without a Charcot foot: An 8.5-year prospective case-control study.

BACKGROUND AND AIMS: Charcot foot is a rare but severe complication to diabetes and peripheral neuropathy. It is still unclear if an acute Charcot foot has long-term effects on the bone metabolism. To investigate this, we conducted a follow-up study to examine if a previously acute Charcot foot has any long-term effects on bone mineral density (BMD) or local or systemic bone metabolism. METHODS: An 8.5-year follow-up case-control study of 44 individuals with diabetes mellitus, 24 of whom also had acute or chronic Charcot foot at the baseline visit in 2005-2007, who were followed up in 2015 with DXA scans and blood samples. RESULTS: 21 of the 44 baseline participants participated in the follow-up. There were no difference in the change in total hip BMD from baseline to follow-up in either the Charcot or the control group (p = 0.402 and 0.517), and no increased risk of osteoporosis in the previous Charcot feet either. From baseline to follow-up, there was a significant difference in the change in levels of fsRANK-L in the Charcot group, but not in the control group (p = 0.002 and 0.232, respectively). At follow-up, there were no differences in fsRANK-L between the groups. The fsRANK-L/OPG ratio also significantly decreased from baseline to follow-up in the Charcot group (3.4 versus 0.5) (p = 0.009), but not in the control group (1.3 versus 1.1) (p = 0.302). CONCLUSION: We found that diabetes patients with an acute Charcot foot have an elevated fsRANK-L/OPG ratio, and that the level decreased from baseline to follow-up to be comparable to the level in diabetes patients without previous or current Charcot foot. We found no permanent effect of an acute Charcot foot on hip or foot BMD.

[Work-up of thyroid incidentalomas identified by 18F-fluorodeoxyglucose PET/CT].

Several reports have described dramatic increase over recent decades in the incidence of thyroid cancer, even as thyroid cancer-related mortality rates have not changed substantially. Nevertheless, in several retrospective studies the incidence of malignancy in focal 18F-fluorodeoxyglucose (FDG) thyroid uptake discovered on whole body 18F-FDG PET/CT, carried out for non-thyroid cancers, is 13-64%. Our aim was to design a practical algorithm for management of an increasing number of thyroid incidentalomas, identified by 18F-FDG PET/CT.

The Gluco- and Liporegulatory and Vasodilatory Effects of Glucose-Dependent Insulinotropic Polypeptide (GIP) Are Abolished by an Antagonist of the Human GIP Receptor.

A truncated form of human glucose-dependent insulinotropic polypeptide (GIP), GIP(3-30)NH2, was recently identified as an antagonist of the human GIP receptor. This study examined the ability of GIP(3-30)NH2 to antagonize the physiological actions of GIP in glucose metabolism, subcutaneous abdominal adipose tissue blood flow (ATBF), and lipid metabolism in humans. Eight lean subjects were studied by measuring arteriovenous concentrations of metabolites and ATBF on three different occasions during hyperglycemic-hyperinsulinemic clamps with concomitant infusions of GIP, GIP(3-30)NH2, or both GIP and GIP(3-30)NH2 During infusion of GIP(3-30)NH2 alone and in combination with GIP, insulin levels and the total glucose amount infused to maintain the clamp were lower than during GIP alone. In addition, ATBF remained constant during the antagonist and increased only slightly in combination with GIP, whereas it increased fivefold during GIP alone. Adipose tissue triacylglyceride (TAG) and glucose uptake decreased, and the free fatty acid/glycerol ratio increased during the antagonist alone and in combination with GIP. The changes in glucose infusion rates and plasma insulin levels demonstrate an inhibitory effect of the antagonist on the incretin effect of GIP. In addition, the antagonist inhibited GIP-induced increase in ATBF and decreased the adipose tissue TAG uptake, indicating that GIP also plays a crucial role in lipid metabolism.

A sandwich ELISA for measurement of the primary glucagon-like peptide-1 metabolite.

Glucagon-like peptide-1 (GLP-1) is an incretin hormone secreted from the gastrointestinal tract. It is best known for its glucose-dependent insulinotropic effects. GLP-1 is secreted in its intact (active) form (7-36NH2) but is rapidly degraded by the dipeptidyl peptidase 4 (DPP-4) enzyme, converting >90% to the primary metabolite (9-36NH2) before reaching the targets via the circulation. Although originally thought to be inactive or antagonistic, GLP-1 9-36NH2 may have independent actions, and it is therefore relevant to be able to measure it. Because reliable assays were not available, we developed a sandwich ELISA recognizing both GLP-1 9-36NH2 and nonamidated GLP-1 9-37. The ELISA was validated using analytical assay validation guidelines and by comparing it to a subtraction-based method, hitherto employed for estimation of GLP-1 9-36NH2 Its accuracy was evaluated from measurements of plasma obtained during intravenous infusions (1.5 pmol × kg-1 × min-1) of GLP-1 7-36NH2 in healthy subjects and patients with type 2 diabetes. Plasma levels of the endogenous GLP-1 metabolite increased during a meal challenge in patients with type 2 diabetes, and treatment with a DPP-4 inhibitor fully blocked its formation. Accurate measurements of the GLP-1 metabolite may contribute to understanding its physiology and role of GLP-1 in diabetes.