Influence of uremia and hemodialysis on the turnover and metabolic effects of glucagon

Glucagon Clearance Is Decreased in Chronic Kidney Disease but Preserved in Liver Cirrhosis

It is not completely clear which organs are responsible for glucagon elimination in humans, and disturbances in the elimination of glucagon could contribute to the hyperglucagonemia observed in chronic liver disease and chronic kidney disease (CKD). Here, we evaluated kinetics and metabolic effects of exogenous glucagon in individuals with stage 4 CKD (n = 16), individuals with Child-Pugh A-C cirrhosis (n = 16), and matched control individuals (n = 16), before, during, and after a 60-min glucagon infusion (4 ng/kg/min). Individuals with CKD exhibited a significantly lower mean metabolic clearance rate of glucagon (14.0 [95% CI 12.2;15.7] mL/kg/min) compared with both individuals with cirrhosis (19.7 [18.1;21.3] mL/kg/min, P < 0.001) and control individuals (20.4 [18.1;22.7] mL/kg/min, P < 0.001). Glucagon half-life was significantly prolonged in the CKD group (7.5 [6.9;8.2] min) compared with individuals with cirrhosis (5.7 [5.2;6.3] min, P = 0.002) and control individuals (5.7 [5.2;6.3] min, P < 0.001). No difference in the effects of exogenous glucagon on plasma glucose, amino acids, or triglycerides was observed between groups. In conclusion, CKD, but not liver cirrhosis, leads to a significant reduction in glucagon clearance, supporting the kidneys as a primary site for human glucagon elimination.

ARTICLE HIGHLIGHTS

The Effect of Nutrition and Exercise on Body Composition, Exercise Capacity, and Physical Functioning in Advanced CKD Patients

Patients with stages 4 and 5 chronic kidney disease (CKD), and particularly chronic dialysis patients, commonly are found to have substantially reduced daily physical activity in comparison to age- and sex-matched normal adults. This reduction in physical activity is associated with a major decrease in physical exercise capacity and physical performance. The CKD patients are often physically deconditioned, and protein energy wasting (PEW) and frailty are commonly present. These disorders are of major concern because physical dysfunction, muscle atrophy, and reduced muscle strength are associated with poor quality of life and increased morbidity and mortality in CKD and chronic dialysis patients. Many randomized controlled clinical trials indicate that when CKD and chronic dialysis are provided nutritional supplements or undergo exercise training their skeletal muscle mass and exercise capacity often increase. It is not known whether the rise in skeletal muscle mass and exercise capacity associated with nutritional support or exercise training will reduce morbidity or mortality rates. A limitation of these clinical trials is that the sample sizes of the different treatment groups were small. The aim of this review is to discuss the effects of nutrition and exercise on body composition, exercise capacity, and physical functioning in advanced CKD patients.

13C15N: glucagon-based novel isotope dilution mass spectrometry method for measurement of glucagon metabolism in humans

Background

Glucagon serves as an important regulatory hormone for regulating blood glucose concentration with tight feedback control exerted by insulin and glucose. There are critical gaps in our understanding of glucagon kinetics, pancreatic α cell function and intra-islet feedback network that are disrupted in type 1 diabetes. This is important for translational research applications of evolving dual-hormone (insulin + glucagon) closed-loop artificial pancreas algorithms and their usage in type 1 diabetes. Thus, it is important to accurately measure glucagon kinetics in vivo and to develop robust models of glucose-insulin-glucagon interplay that could inform next generation of artificial pancreas algorithms.

Methods

Here, we describe the administration of novel ¹³C¹⁵N heavy isotope-containing glucagon tracers—FF glucagon [(Phe 6 ¹³C₉,¹⁵N; Phe 22 ¹³C₉,¹⁵N)] and FFLA glucagon [(Phe 6 ¹³C₉,¹⁵N; Phe 22 ¹³C₉,¹⁵N; Leu 14 ¹³C₆,¹⁵N; Ala 19 ¹³C₃)] followed by anti-glucagon antibody-based enrichment and LC–MS/MS based-targeted assays using high-resolution mass spectrometry to determine levels of infused glucagon in plasma samples. The optimized assay results were applied for measurement of glucagon turnover in subjects with and without type 1 diabetes infused with isotopically labeled glucagon tracers.

Results

The limit of quantitation was found to be 1.56 pg/ml using stable isotope-labeled glucagon as an internal standard. Intra and inter-assay variability was < 6% and < 16%, respectively, for FF glucagon while it was < 5% and < 23%, respectively, for FFLA glucagon. Further, we carried out a novel isotope dilution technique using glucagon tracers for studying glucagon kinetics in type 1 diabetes.

Conclusions

The methods described in this study for simultaneous detection and quantitation of glucagon tracers have clinical utility for investigating glucagon kinetics in vivo in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-022-09344-2.

The association of glucagon with disease severity and progression in patients with autosomal dominant polycystic kidney disease: an observational cohort study

Background

Mammalian target of rapamycin (mTOR) inhibitors and ketogenesis have been shown to ameliorate disease progression in experimental autosomal dominant polycystic kidney disease (ADPKD). Glucagon is known to lower mTOR activity and stimulate ketogenesis. We hypothesized that in ADPKD patients, higher endogenous glucagon is associated with less disease severity and progression.

Methods

Data were analysed from 664 Dutch ADPKD patients participating in the Developing Intervention Strategies to Halt Progression of ADPKD observational cohort, including patients >18 years of age with an estimated glomerular filtration rate (eGFR) ≥15 mL/min/1.73 m² and excluding patients with concomitant diseases or medication use that may impact the natural course of ADPKD. The association between glucagon and disease severity and progression was tested using multivariate linear regression and mixed modelling, respectively.

Results

The median glucagon concentration was 5.0 pmol/L [interquartile range (IQR) 3.4-7.2) and differed significantly between females and males [4.3 pmol/L (IQR 2.9-6.0) and 6.6 (4.5-9.5), P < 0.001, respectively]. Intrasubject stability of glucagon in 30 patients showed a strong correlation (Pearson's correlation coefficient 0.893; P < 0.001). Moreover, glucagon showed significant associations with known determinants (sex, body mass index and copeptin; all P < 0.01) and known downstream effects (glucose, haemoglobin A1c and cholesterol; all P < 0.05), suggesting that glucagon was measured reliably. Cross-sectionally, glucagon was associated with eGFR and height-adjusted total kidney volume, but in the opposite direction of our hypothesis, and these lost significance after adjustment for confounders. Glucagon was not associated with an annual decline in kidney function or growth in kidney volume.

Conclusions

These data do not provide evidence for a role of endogenous glucagon as a protective hormone in ADPKD. Intervention studies are needed to determine the relation between glucagon and ADPKD.

Glucagon Clearance is Preserved in Type 2 Diabetes

Hyperglucagonemia is a common observation in both obesity and type 2 diabetes, and the etiology is primarily thought to be hypersecretion of glucagon. We investigated whether altered elimination kinetics of glucagon could contribute to the hyperglucagonemia in type 2 diabetes and obesity. Individuals with type 2 diabetes and preserved kidney function (8 with and 8 without obesity) and matched control individuals (8 with and 8 without obesity) were recruited. Each participant underwent a 1-hour glucagon infusion (4 ng/kg/min), achieving steady-state plasma glucagon concentrations, followed by a 1-hour wash-out period. Plasma levels, the metabolic clearance rate (MCR), half-life (T½) and volume of distribution of glucagon were evaluated and a pharmacokinetic model was constructed. Glucagon MCR and volume of distribution were significantly higher in the type 2 diabetes group compared to the control group, while no significant differences between the groups were found in glucagon T½. Individuals with obesity had neither a significantly decreased MCR, T½, nor volume of distribution of glucagon. In our pharmacokinetic model, glucagon MCR associated positively with fasting plasma glucose and negatively with body weight. In conclusion, our results suggest that impaired glucagon clearance is not a fundamental part of the hyperglucagonemia observed in obesity and type 2 diabetes.

Yi-Qi-Jian-Pi-Xiao-Yu-Xie-Zhuo Formula Improves Muscle Atrophy via Modulating the IGF-1/PI3K/Akt Signaling Pathway in 5/6 Nephrectomized Rats

The Yi–Qi–Jian–Pi–Xiao–Yu–Xie–Zhuo (YQJPXYXZ) formula has been used for treating chronic kidney disease (CKD) for many years with good efficiency based on the cumulative empirical experience of previous practitioners. Impairment of the IGF-1/PI3K/Akt signaling pathway plays an important role in mediating muscle wasting. This study aimed to observe effects of the YQJPXYXZ formula on muscle atrophy in CKD rats and investigate its possible mechanism on regulation of the IGF-1/PI3K/Akt signaling pathway. The 5/6 nephrectomized rats were randomly allocated into 3 groups: the CKD group, the KT (compound α-ketoacid tablets) group, and the YQJPXYXZ group. Besides, sham-operated rats were included as the sham group. All rats were treated for 12 weeks. Results showed that administration of the YQJPXYXZ formula prevented body weight loss and muscle fiber size decrease. Moreover, the YQJPXYXZ formula increased the IGF-1 level of serum and skeletal muscle in CKD rats and enhanced the phosphorylation level of Akt. Furthermore, the YQJPXYXZ formula decreased the Atrogin1 and MuRF1 mRNA and MuRF1 proteins. In conclusion, our data demonstrated that the YQJPXYXZ formula improves muscle wasting in CKD rats, which might be associated with the modulation of the IGF-1/PI3K/Akt signaling pathway and inhibition of the ubiquitin–proteasome system (UPS).

A multivariate factor analysis of the high plasma concentration of cyclic AMP in patients with chronic renal failure

The concentration of cyclic AMP which is known as an intracellular mediator of hormone action increased in the plasma of patients with chronic renal failure (CRF). In the present study, the plasma concentration of cyclic AMP significantly correlated not only with serum, creatinine, and urea levels, but also with plasma PTH and glucagon in patients with CRF. Furthermore, plasma concentrations of PTH and glucagon correlated with the serum creatinine concentration to a significant extent.

To discuss the cause of the increased cyclic AMP concentration in plasma of patients with CRF, multivariate analyses were carried out on the obtained clinical data from patients and normal subjects. In the factor analysis on the clinical data from 61 subjects, cyclic AMP, creatinine and BUN correlated with the first factor and PTH correlated with the second factor. The cumulative contribution ratio by the second factor was 76%. The results of the cluster analysis indicated that cyclic AMP, creatinine, and BUN formed a cluster and PTH glucagon made another cluster. These results suggest that the elevated plasma concentration of cyclic AMP in patients with CRF was mainly introduced not by overproduction but by the retention of cyclic AMP due to the decreased renal function.

An Amino Acid-Based Peritoneal Dialysis Fluid Buffered with Bicarbonate versus Glucose/Bicarbonate and Glucose/Lactate Solutions: An Intraindividual Randomized Study

Objective

In order to study acute metabolic changes and peritoneal transport, amino acids as osmotic agent and bicarbonate as buffer were tested as new agents in peritoneal dialysis (PD) solutions.

Design

In a prospective, cross-over, randomized, intraindividual study, we investigated the acute metabolic changes following the application of three different PD fluids: (1) a 1% amino acid-based PD solution buffered with bicarbonate (34 mmol/L) (Amino/Bic); (2) a 1.5% glucose anhydrous-containing bicarbonate-buffered solution (34 mmol/L) (Glu/Bic); and (3) a conventional 1.5% glucose anhydrous-based dialysis solution with lactate (35 mmol/L) (Glu/Lac).

Setting

University medical center.

Patients

Ten nondiabetic patients stable on continuous ambulatory peritoneal dialysis (time on dialysis, 42.5 ± 21.5 months) were treated and monitored with the test solutions over a 6-hour dwell. Three different study days followed in a randomized order for each patient (interval of 1 – 3 weeks). Blood and dialysate samples were taken at 0.25, 0.5, 1, 2, 4, and 6 hours. Immediately after the 1-hr dwell (and after sampling), the patients received a standardized breakfast, thereby simulating usual food intake.

Results

Following the application of Amino/Bic a significant increase in plasma amino acids occurred, with peak levels (maximum 250% increase) after either the 1-hr or the 2-hr dwell. Before taking the standard meal (0.5 hr, 1 hr), the mean serum glucose level with Amino/Bic was 8% ± 13% lower than with Glu/Bic ( p = 0.06) and 14% ± 8% lower than with Glu/Lac ( p < 0.01). This difference was still significant after the standard breakfast and also for the whole dwell (average serum glucose 0.5 – 6 hr: Amino/Bic, 91 ± 6 mg/dL; Glu/Bic, 100 ± 8 mg/dL; Glu/Lac, 102 ± 7 mg/dL; p < 0.01 MANOVA). The serum insulin profiles did not differ between the fluids. A transperitoneal protein- and amino acid-related nitrogen loss of 0.49 ± 0.18 g and 0.48 ± 0.12 g per dwell was measured using Glu/Bic and Glu/Lac, while a positive balance of 1.80 ± 0.43 g was achieved with Amino/ Bic. The parameters of acid-base status (pH, HCO3, pCO2) remained nearly unchanged in the blood, irrespective of the solution used, while dialysate values differed markedly. No significant differences with respect to ultrafiltration (Amino/Bic, –68 ± 199 mL/6hr; Glu/Bic, –51 ± 89 mL/6hr; Glu/ Lac, –2 ± 134 mL/6hr) and peritoneal creatinine clearance (Amino/Bic, 4.9 ± 0.6 mL/min; Glu/Bic, 5.1 ± 0.6 mL/min; Glu/ Lac, 4.8 ± 0.5 mL/min) were measured.

Conclusions

Our results demonstrate that ultrafiltration and small solute clearance over a 6-hour dwell with a 1% Amino/Bic solution were comparable to those of 1.5% Glu/Bic and 1.5% Glu/Lac. Reduced serum glucose concentrations were found with Amino/Bic and this fluid compensated the transperitoneal protein-nitrogen loss of about three glucose dwells. Bicarbonate buffering (34 mmol/L) did not change blood acid-base status combined with either glucose or amino acids.

Frequency and Causes of False-Positive Elevated Plasma Concentrations of Fasting Gut Hormones in a Specialist Neuroendocrine Tumor Center

INTRODUCTION

In the UK, the fasting plasma concentrations of a panel of gut hormones (comprising vasoactive intestinal peptide (VIP), gastrin, pancreatic polypeptide (PP), glucagon, somatostatin and chromogranin A) are measured to evaluate patients who have or who (due to unexplained and compatible symptoms) are suspected of having neuroendocrine tumors (NETs). False positive elevated hormone concentrations are sometimes found.

OBJECTIVE

To evaluate the frequency and implications of false positive fasting gut hormone results.

METHODS

Retrospective audit of fasting gut hormone profile results at a large UK university teaching hospital over 12 months.

RESULTS

Fasting gut hormone concentrations were measured in 231 patients during 2017. No NETs were found in the 88 patients who had this test performed only to investigate symptoms. 31 false positive gastrin, 8 false positive chromogranin A, two false positive glucagon, three false positive somatostatin, one false positive PP, and one false positive VIP results were found. We extended the audit for glucagon and somatostatin for an additional two years and found seven probable false-positive raised glucagon concentrations and four probable false-positive elevated plasma somatostatin concentrations in total.

CONCLUSIONS

False-positive elevations of plasma gastrin and chromogranin A were common and causes such as proton pump inhibitor use or inadequate fasting accounted for most cases. Elevated plasma concentrations of the other gut hormones were also detected in patients who had no other evidence of NET. Other diagnoses (e.g. cirrhosis and medullary thyroid carcinoma for hypersomatostatinemia and type 2 diabetes mellitus, pancreatitis, liver or renal impairment for hyperglucagonemia) may cause these false positive results.

Relationship Between Fasting Plasma Glucagon Level and Renal Function-A Cross-Sectional Study in Individuals With Type 2 Diabetes

Background and Aim

The kidney is the main site for glucagon clearance. However, a recent study showed that hyperglucagonemia in patients with end-stage renal disease might not be caused by full-length intact glucagon. Additionally, the relationship between glucagon and renal function in early-stage chronic kidney disease (CKD) has not yet been characterized. We studied the association of fasting glucagon with renal function across a wide range of glomerular filtration rates (GFRs) in participants with type 2 diabetes.

Participants and Methods

326 participants with type 2 diabetes and renal function spanning CKD stage 1 to 5 were included in the present cross-sectional study. Fasting full-length plasma glucagon was quantified using a newly developed ELISA (Mercodia AB, Uppsala, Sweden).

Results

The fasting plasma glucagon level was elevated linearly from CKD stage 1 to 5 [from a median of 2.5 pM (interquartile range, 1.4 to 4.7) in CKD 1 to a median of 8.3 pM (interquartile range, 5.9 to 12.8) in CKD 5; P for trend < 0.0001], from as early as CKD stage 2 compared with that in stage 1 (Bonferroni-corrected P < 0.0001). The estimated GFR and homeostatic model of assessment–insulin resistance were the main determinants of the fasting glucagon level. These explained 14.3% and 10.3% of the glucagon variance, respectively. Albuminuria was not associated with fasting glucagon after adjustment for estimated GFR.

Conclusions

Fasting full-length glucagon was elevated linearly with the deterioration in renal function in individuals with type 2 diabetes, even in those with early CKD. In addition to renal function, insulin sensitivity was also a main determinant of glucagon variance.

Hemodynamic Effects of Glucagon: A Literature Review

CONTEXT

Glucagon's effects on hemodynamic parameters, most notably heart rate and cardiac contractility, are often overlooked. The glucagon receptor is a central target in novel and anticipated type 2 diabetes therapies, and hemodynamic consequences of glucagon signaling have therefore become increasingly important. In this review, we summarize and evaluate published studies on glucagon pharmacology with a focus on clinical hemodynamic effects in humans.

EVIDENCE ACQUISITION

PubMed, Embase, and the Cochrane Library were searched for clinical studies concerning hemodynamic effects of glucagon (no year restriction). Papers reporting effects of a defined glucagon dose on any hemodynamic parameter were included. Reference searches were conducted in retrieved articles.

EVIDENCE SYNTHESIS

Hemodynamic effects of glucagon have been investigated mainly in cohort studies of patients suffering from heart failure receiving large glucagon bolus injections. The identified studies had shortcomings related to restricted patient groups, lack of a control group, randomization, or blinding. We identified no properly conducted randomized clinical trials. The majority of human studies report stimulating effects of pharmacological glucagon doses on heart rate, cardiac contractility, and blood pressure. The effects were characterized by short duration, interindividual variation, and rapid desensitization. Some studies reported no measurable effects of glucagon.

CONCLUSIONS

The level of evidence regarding hemodynamic effects of glucagon is low, and observations in published studies are inconsistent. Actual effects, interindividual variation, dose-response relationships, and possible long-term effects of supraphysiological glucagon levels warrant further investigation.

Glucagon sensitivity and clearance in type 1 diabetes: insights from in vivo and in silico experiments

Glucagon use in artificial pancreas for type 1 diabetes (T1D) is being explored for prevention and rescue from hypoglycemia. However, the relationship between glucagon stimulation of endogenous glucose production (EGP) viz., hepatic glucagon sensitivity, and prevailing glucose concentrations has not been examined. To test the hypothesis that glucagon sensitivity is increased at hypoglycemia vs. euglycemia, we studied 29 subjects with T1D randomized to a hypoglycemia or euglycemia clamp. Each subject was studied at three glucagon doses at euglycemia or hypoglycemia, with EGP measured by isotope dilution technique. The peak EGP increments and the integrated EGP response increased with increasing glucagon dose during euglycemia and hypoglycemia. However, the difference in dose response based on glycemia was not significant despite higher catecholamine concentrations in the hypoglycemia group. Knowledge of glucagon's effects on EGP was used to develop an in silico glucagon action model. The model-derived output fitted the obtained data at both euglycemia and hypoglycemia for all glucagon doses tested. Glucagon clearance did not differ between glucagon doses studied in both groups. Therefore, the glucagon controller of a dual hormone control system may not need to adjust glucagon sensitivity, and hence glucagon dosing, based on glucose concentrations during euglycemia and hypoglycemia.

Postprandial responses of incretin and pancreatic hormones in non-diabetic patients with end-stage renal disease

BACKGROUND

Patients with end-stage renal disease (ESRD) have glucometabolic disturbances resulting in a high prevalence of prediabetes. The underlying pathophysiology remains unclear, but may prove important for the strategies employed to prevent progression to overt diabetes. Meal-induced release of the insulinotropic gut-derived incretin hormones and pancreatic hormones play a critical role in the maintenance of a normal postprandial glucose tolerance.

METHODS

We studied patients with ESRD and either normal (n = 10) or impaired (n = 10) glucose tolerance, and control subjects (n = 11). Plasma concentrations of glucose, insulin, glucagon, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and paracetamol were measured repeatedly during a standardized 4-h liquid meal including 1.5 g paracetamol (added for evaluation of gastric emptying).

RESULTS

Fasting glucose and postprandial glucose responses were comparable between groups (P > 0.082). Patients with ESRD exhibited higher fasting levels of GIP and glucagon compared with controls (P < 0.001). Baseline-corrected GLP-1 and glucagon responses were enhanced (P < 0.002), baseline-corrected insulin responses and insulin excursions were reduced (P < 0.035), and paracetamol excursions were delayed (P < 0.024) in patients with ESRD compared with controls. None of the variables differed between the two ESRD subgroups.

CONCLUSIONS

Non-diabetic patients with ESRD were characterized by reduced postprandial insulin responses despite increased secretion of the insulinotropic incretin hormone GLP-1. Fasting levels and baseline-corrected responses of glucagon were elevated and gastric emptying was delayed in the ESRD patients. These perturbations seem to be caused by uraemia per se and may contribute to the disturbed glucose metabolism in ESRD patients.

Gastrointestinal factors contribute to glucometabolic disturbances in nondiabetic patients with end-stage renal disease

Nondiabetic patients with end-stage renal disease (ESRD) have disturbed glucose metabolism, the underlying pathophysiology of which is unclear. To help elucidate this, we studied patients with ESRD and either normal or impaired glucose tolerance (10 each NGT or IGT, respectively) and 11 controls using an oral glucose tolerance test and an isoglycemic intravenous glucose infusion on separate days. Plasma glucose, insulin, glucagon, and incretin hormones were measured repeatedly, and gastrointestinal-mediated glucose disposal (GIGD) based on glucose amounts utilized, and incretin effect based on incremental insulin responses, were calculated. The GIGD was significantly reduced in both ESRD groups compared with controls. Incretin effects were 69% (controls), 55% (ESRD with NGT), and 41% (ESRD with IGT), with a significant difference between controls and ESRDs with IGT. Fasting concentrations of glucagon and incretin hormones were significantly increased in patients with ESRD. Glucagon suppression was significantly impaired in both groups with ESRD compared with controls, while the baseline-corrected incretin hormone responses were unaltered between groups. Thus, patients with ESRD had reduced GIGD, a diminished incretin effect in those with IGT, and severe fasting hyperglucagonemia that seemed irrepressible in response to glucose stimuli. These factors may contribute to disturbed glucose metabolism in ESRD.

Glucagon effects on plasma cyclic AMP and other reactants in normals and low insulin responders

The metabolic response to i.v. glucagon was evaluated in 11 normal individuals and 8 healthy low insulin responders. Elevations of plasma cyclic AMP and blood glucose were similar in both groups. Accordingly, no indications were seen of differing hepatic responsiveness to glucagon. In contrast, the groups differed in the course of plasma glycerol during the test.

A proposed nomenclature and diagnostic criteria for protein-energy wasting in acute and chronic kidney disease

The recent research findings concerning syndromes of muscle wasting, malnutrition, and inflammation in individuals with chronic kidney disease (CKD) or acute kidney injury (AKI) have led to a need for new terminology. To address this need, the International Society of Renal Nutrition and Metabolism (ISRNM) convened an expert panel to review and develop standard terminologies and definitions related to wasting, cachexia, malnutrition, and inflammation in CKD and AKI. The ISRNM expert panel recommends the term 'protein-energy wasting' for loss of body protein mass and fuel reserves. 'Kidney disease wasting' refers to the occurrence of protein-energy wasting in CKD or AKI regardless of the cause. Cachexia is a severe form of protein-energy wasting that occurs infrequently in kidney disease. Protein-energy wasting is diagnosed if three characteristics are present (low serum levels of albumin, transthyretin, or cholesterol), reduced body mass (low or reduced body or fat mass or weight loss with reduced intake of protein and energy), and reduced muscle mass (muscle wasting or sarcopenia, reduced mid-arm muscle circumference). The kidney disease wasting is divided into two main categories of CKD- and AKI-associated protein-energy wasting. Measures of chronic inflammation or other developing tests can be useful clues for the existence of protein-energy wasting but do not define protein-energy wasting. Clinical staging and potential treatment strategies for protein-energy wasting are to be developed in the future.

Carbohydrate metabolism in uraemia

PURPOSE OF REVIEW

Most uraemic patients are insulin resistant. This review focuses on the occurrence, mechanisms and consequences of this insulin resistance. Hypoglycaemia is also possible in a minority of uraemic patients; its causes are discussed at the end of the review.

RECENT FINDINGS

Insulin resistance is detectable when the glomerular filtration rate is below 50 ml/min per 1.73 m in non-diabetic uraemic individuals. Uraemia can alter insulin sensitivity even in diabetic patients; familial insulin resistance may favour the occurrence of diabetic nephropathy. Although reduced glucose non-oxidative disposal is the most evident defect of carbohydrate metabolism, abnormal glucose oxidation, endogenous glucose production and insulin secretion are also contributors. The accumulation of nitrogenous compounds is the most important mechanism of a specific state of insulin resistance in uraemia. Their identification is progressing, particularly in the field of carbamoylated amino acids. The consequences of chronic renal failure such as anaemia, metabolic acidosis and secondary hyperparathyroidism also indirectly play a role.

SUMMARY

The treatment of uraemia by renal replacement therapies or low-protein diets improves insulin sensitivity. However, patients still have a high cardiovascular risk. The identification of the accumulating molecular species that specifically alter insulin sensitivity is therefore of great interest. The favourable effect of non-specific insulin sensitizers such as glitazone may also help to reduce this risk.

Protein and energy nutrition among adult patients treated with chronic peritoneal dialysis

Protein-energy malnutrition (PEM) in adult patients treated with chronic peritoneal dialysis (CPD), which is highly prevalent and frequently severe in its manifestation, poses a significant therapeutic dilemma. The causes of PEM include inflammation, low nutrient intake, nutrient losses during dialysis, metabolic acidemia, coexisting illnesses, and possibly the endocrine disorders of uremia. Treatment strategies for PEM in CPD patients include the following: attempt to treat the potentially reversible causes of anorexia, increase nutrient intake (by nutritional counseling, oral food supplements, consideration of appetite stimulants and intraperitonial amino acid solutions), and the correction of metabolic acidosis. Coexisting illnesses engendering PEM should be treated. Experimental evidence suggests that such agents as anabolic steroids, human growth hormone, insulin-like growth factor-I, and L-carnitine may engender positive protein balance in these individuals. Finally, the use of anti-inflammatory agents to improve the nutritional status of malnourished CPD patients remains to be defined. There is a need to carry out clinical trials that examine whether an improvement in the nutritional status of CPD patients is associated with an improvement in their mortality, morbidity and/or quality of life.

The National Kidney Foundation K/DOQI clinical practice guidelines for dietary protein intake for chronic dialysis patients

This paper discusses two of the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) clinical practice guidelines for nutrition in chronic renal failure. These are the guidelines that recommend a dietary protein intake of 1.2 g protein/kg body weight/day for clinically stable maintenance hemodialysis (MHD) patients (Guideline 15) and 1.2 to 1.3 g protein/kg/day for clinically stable chronic peritoneal dialysis (CPD) patients (Guideline 16). These recommended protein intakes are greater than the usually ingested protein intakes of MHD and CPD patients and are also greater than the recommended protein intakes for healthy, nonpregnant, nonlactating adults. The possible mechanisms that engender these increased protein needs include (1) the substantial quantity of amino acids, peptides, and proteins removed by the dialysis procedure and (2) the protein catabolic or antianabolic state caused by the uremic milieu, the inflammatory state, the oxidative and carbonyl stress, and the bioincompatible dialysis materials to which MHD and CPD patients are exposed. There are a number of nitrogen balance studies that have been performed to identify the dietary protein needs of MHD and CPD patents. The results of this research as well as some of the methodological limitations of these studies are reviewed. The concepts of the average dietary protein intake required to maintain protein balance in MHD or CPD patients and the safe protein intake that will maintain protein balance in virtually all MHD and CPD patients are discussed.

Pathophysiology of protein-energy wasting in chronic renal failure

There is a high prevalence of protein-energy malnutrition in both nondialyzed patients with advanced chronic renal failure and in those individuals with end-stage renal disease who are receiving maintenance hemodialysis or chronic peritoneal dialysis therapy. Approximately one-third of maintenance dialysis patients have mild to moderate protein-energy malnutrition, and about 6 to 8 percent of these individuals have severe malnutrition. These statistics are of major concern because markers of protein-energy malnutrition are strong predictors of morbidity and mortality. The causes of protein-energy malnutrition in patients with chronic renal failure include: (1) decreased energy or protein intake; (2) concurrent chronic illnesses, and superimposed acute illnesses and possibly increased inflammatory cytokines; (3) the catabolic stimulus of hemodialysis; (4) losses of nutrients into dialysate, particularly amino acids, peptides, protein (with peritoneal dialysis), glucose (when hemodialysis is performed with glucose-free dialysate) and water-soluble vitamins; and (5) diagnostic or therapeutic (e.g., prednisone therapy) procedures that reduce nutrient intake or engender net protein breakdown. Other theoretically possible causes for protein-energy malnutrition include (6) chronic blood loss; (7) endocrine disorders (especially resistance to insulin and insulin-like growth factor-I, hyperglucagonemia, hyperparathyroidism and deficiency of 1,25-dihydroxycholecalciferol); (8) products of metabolism that accumulate in renal failure and may induce wasting, such as organic and inorganic acids; (9) loss of the metabolic actions of the kidney; and (10) the accumulation of toxic compounds that are taken up from the environment (e.g., aluminum).

Somatostatin release in response to glucose is impaired in chronic renal failure

In order to evaluate somatostatin (SRIH) secretion in uremia, plasma SRIH concentrations were determined in basal conditions and after an oral glucose tolerance test (OGTT) in 14 non-dialysed patients with chronic renal failure (CRF), seven of whom had normal glucose tolerance (NGT) and seven impaired glucose tolerance (IGT). Plasma insulin, C-peptide and glucagon and blood glucose concentrations were also evaluated. The results were compared with those obtained in a group of age- and sex-matched normal subjects. In CRF patients, plasma SRIH fasting values (8.6 +/- 0.6 and 7.8 +/- 0.6 pmol/L in NGT and IGT patients, respectively) were comparable to those recorded in controls (7.7 +/- 0.5 pmol/L). SRIH response to OGTT, evaluated as area under curves (AUC) above basal, was similar in both groups of CRF patients (412.9 +/- 84.5 and 415.6 +/- 51.9 pmol/L per min), and significantly lower than in controls (660.1 +/- 58.5 pmol/L per min). Data indicate that chronic uremia induces a loss of SRIH secretory cell responsiveness to glucose. A possible effect of impaired SRIH secretion on glucose metabolism in CRF is discussed.

Effect of glucagon on protein synthesis in human rectal cancer in situ

OBJECTIVE

The purpose of this study was to determine the effect of glucagon or placebo on the rate of tumor fractional protein synthesis in situ in patients with localized rectal cancer who were not malnourished, demonstrated normal glucagon concentrations, and could therefore be used as a model to study the glucagon effect.

SUMMARY BACKGROUND DATA

Cancer cachexia is associated with an increased concentration of counterregulatory hormones, including glucagon. This altered hormonal milieu may not only contribute to malnutrition, but also promote tumor growth, because previous experimental work suggests that glucagon can cause human colorectal tumor cells to proliferate. Corresponding mechanisms in vivo have, thus far, not been investigated.

METHODS

Advanced mass spectrometry techniques (capillary gas chromatography [GC]/combustion isotope ratio mass spectrometry [IRMS]) were used to determine directly the incorporation rate of 1-[13C]-leucine into tissue protein. Because GC/IRMS requires only a small sample volume, three consecutive endoscopic biopsies could be obtained from the same tumor to determine isotopic enrichments at baseline, after a 4-hour glucagon infusion (3 ng/kg/min), or after placebo.

RESULTS

In patients with localized rectal cancer, glucagon caused the tumor fractional protein synthetic rate to double (2.25+/-0.49 %/hr, p < 0.05 vs. 1.16+/-0.30 basal). In contrast, tumor protein synthesis declined over time in controls (placebo) (0.67+/-0.09 %/hr, p < 0.05 vs. 1.11+/-0.16 basal).

CONCLUSIONS

Tumor protein synthesis and growth can be stimulated by glucagon in situ. Therefore, elevated glucagon concentrations in cachectic cancer patients should be considered detrimental and attempts made to prevent this specific response of the body to the malignant disease.

Insulin secretory capacity and the regulation of glucagon secretion in diabetic and non-diabetic alcoholic cirrhotic patients

BACKGROUND/AIMS

Insulin secretion is increased in cirrhotic patients without diabetes but decreased in cirrhotic patients with diabetes. Increased glucagon secretion is found in both groups. Our aim was to determine: 1) whether alterations in insulin secretion are due to changes in maximal secretory capacity or altered islet B-cell sensitivity to glucose, and 2) whether regulation of glucagon secretion by glucose is disturbed.

METHODS

Insulin, C-peptide and glucagon levels were measured basally and during 12, 19 and 28 mmol/l glucose clamps, and in response to 5 g intravenous arginine basally and after 35 min at a glucose of 12, 19 and 28 mmol/l in 6 non-diabetic alcoholic cirrhotic patients, six diabetic alcoholic cirrhotic patients and six normal controls.

RESULTS

Fasting insulin, and C-peptide levels were higher in cirrhotic patients than controls but not different between diabetic and non-diabetic patients. C-peptide levels at t=35 min of the clamp increased more with glucose concentration in non-diabetic cirrhotic patients than controls; there was little increase in diabetic cirrhotic patients. At a blood glucose of approximately 5 mmol/l the 2-5 min C-peptide response to arginine (CP[ARG]) was similar in all groups, but enhancement of this response by glucose was greater in non-diabetic cirrhotic patients and impaired in diabetic cirrhotic patients. Maximal insulin secretion (CP(ARG) at 28 mmol/l glucose) was 49% higher in the non-diabetic cirrhotic patients than controls (p<0.05); in diabetic cirrhotic patients it was 47% lower (p<0.05). The glucose level required for half-maximal potentiation of (CPARG) was not different in the three groups. Cirrhotic patients had higher fasting glucagon levels, and a greater 2-5-min glucagon response to arginine, which was enhanced by concomitant diabetes (p<0.001 vs controls). Suppression of plasma glucagon by hyperglycaemia was markedly impaired in diabetic cirrhotic patients (glucagon levels at 35 min of 28 mmol/l glucose clamp: diabetics, 139 x/divided by 1.25 ng/l, non-diabetic cirrhotic patients, 24 x/divided by 1.20, controls, 21 x/divided by 1.15, p<0.001). Suppression of arginine-stimulated glucagon secretion by glucose was also impaired in diabetic cirrhotic patients, and to a lesser extent in non-diabetic cirrhotic patients.

CONCLUSIONS

Insulin secretory abnormalities in diabetic and non-diabetic cirrhotic patients are due to changes in maximal secretory capacity rather than altered B-cell sensitivity to glucose. The exaggerated glucagon response to arginine in alcoholic cirrhotic patients is not abolished by hyperglycaemia/hyperinsulinaemia. In diabetic alcoholic cirrhotic patients, the inhibitory effect of glucose on basal glucagon secretion is also markedly impaired.

Impaired TSH secretion during sustained hyperglucagonemia in anesthetized dogs

We previously demonstrated that hyperglucagonemia may be responsible for thyroid hormone alterations noted in some nonthyroidal illnesses. Since TSH secretion is also known to be altered in many subjects with several nonthyroidal illnesses, we assessed the influence of sustained hyperglucagonemia on TSH secretory pattern in 5 anesthetized dogs. Serum TSH concentrations were determined after a 16-h fast and again at intervals of 15 min during sustained hyperglucagonemia (515-645 pg/mL) induced by iv bolus administration of glucagon 0.1 mg followed by a continuous glucagon infusion 3 ng/kg/min for 3 h. TRH (200 micrograms) was administered iv at 60 min to assess the influence of sustained hyperglucagonemia on the hypothalamic pituitary thyrotroph axis during the study. A control study was also conducted using normal saline instead of glucagon, and both studies were performed in a randomized sequence. Basal TSH levels were not significantly different during both studies. However, serum TSH declined significantly during sustained hyperglucagonemia prior to TRH administration (delta TSH, pre-TRH, -0.86 +/- 0.24 vs 0.02 +/- 0.07 ng/mL for normal saline, p < 0.01). Furthermore, TSH response to iv TRH administration was significantly blunted during glucagon infusion alone as expressed by both the absolute rise (delta TSH, post-TRH, 1.1 +/- 0.5 vs 5.9 +/- 1.7 ng/ml for normal saline, p < 0.01) as well as an integrated response over a 2-h period (sigma TSH, post-TRH, 4.0 +/- 1.1 vs 11.7 +/- 3.5 ng/min/mL, p < 0.001). Therefore, this study demonstrates that sustained hyperglucagonemia inhibits basal TSH secretion as well as TSH response to iv TRH administration, a TSH secretory pattern similar to that noted at the peak of many nonthyroidal illnesses.

Adaptive responses to very low protein diets: the first comparison of ketoacids to essential amino acids

Eight patients with chronic renal failure (GFR 18.8 +/- 2.7 ml/min) were randomized to a crossover comparison of a very low protein diet (VLPD) containing 0.28 g protein and 35 kcal per kg per day, plus an isosmolar mixture of either ketoacids (KA) or essential amino acids (EAA). Subjects initiated the diets 14 days before hospital admission and following a four-day equilibration, a five-day nitrogen balance (BN) was performed. Whole-body protein turnover (WBPT) was measured during fasting and feeding using intravenous [1-13C]leucine and intragastric [5,5,5-2H3]leucine. Even though the VLPD/KA regimen contained 15% less nitrogen, BN was neutral and did not differ between the regimens. Nitrogen conservation with KA was due to a reduction in urea nitrogen appearance. Rates of WBPT measured during fasting and feeding did not differ between the KA or EAA regimens. During both regimens, feeding decreased protein degradation, whereas protein synthesis was unchanged. Although feeding stimulated leucine oxidation, rates were 50 to 100% lower than reported in CRF patients consuming 0.6 or 1.0 g protein/kg/day. Thus, neutral Bn with the VLPD regimen is achieved by a marked reduction in amino acid oxidation and a postprandial inhibition of protein degradation.

Hepatic regulation of pancreatic alpha-cell function

The direct feedback regulation between the endocrine gland and its target organ is an expected biological relationship. However, such a phenomenon is far from being well established in the case of the endocrine pancreas and its major target organ, the liver, especially since plasma glucose has been established as the prime regulator. In this perspective, I have reexamined the feedback regulation between plasma glucose and glucagon secretion by the pancreatic alpha cell. Surprisingly, available data in the literature appear to document a frequent breakdown of this well-established interdependence between plasma glucose and pancreatic alpha cells, as reflected by a sustained elevation of plasma glucagon levels in several physiologic and pathologic states with concurrent euglycemia or hyperglycemia. Moreover, normal or low glucagon concentrations in the presence of fasting hypoglycemia in patients with insulinoma or non-islet cell tumors secreting insulin-like peptides and in patients with hepatic glycogen storage disorders may enhance our hypothesis that plasma glucose level may not be the major regulator of glucagon secretion. Extensive data in the literature show that hyperglucagonemic states are characterized by a unique metabolic environment, namely hepatic glycogen depletion. Similarly, hepatic glycogen stores are abundant in the presence of normal or low glucagon concentrations. These findings imply a distinct relationship between hepatic glycogen content and plasma glucagon level.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of recombinant human growth hormone and intradialytic parenteral nutrition in malnourished hemodialysis patients

Malnutrition in hemodialysis patients is associated with increased morbidity and mortality. The use of intradialytic parenteral nutrition (IDPN) to improve nutritional parameters has been shown to be of limited benefit in most studies. We studied the use of recombinant human growth hormone (rHuGH) in potentiating the effects of IDPN in seven hemodialysis patients dialyzed with a Kt/V of 1.03 +/- 0.11 (mean +/- SEM), but with evidence of malnutrition: albumin, 3.2 +/- 0.18 g/dL; transferrin, 215 +/- 30 mg/dL; insulin-like growth factor-1 (IGF-1), 115 +/- 19 ng/mL, protein catabolic rate (PCR), 0.70 +/- 0.05 g/kg/d; and weight, 12.3% +/- 4.0% below ideal body weight. During 6 weeks of IDPN, resulting in an additional 18 +/- 4 kcal and 0.69 +/- 0.03 g of protein/kg body weight per dialysis session, albumin concentration increased to 3.5 +/- 0.14 g/dL (compared with baseline, P = NS), transferrin increased to 279 +/- 36 mg/dL (P < 0.002), IGF-1 increased to 152 +/- 32 ng/mL (P = NS), and PCR increased to 0.81 +/- 0.04 g/kg/d (P = NS). During the next 6 weeks, IDPN administration was continued and rHuGH, at a dose of 5 mg subcutaneously during each dialysis, was added to the regimen. This resulted in an increase in albumin concentration to 3.8 +/- 0.08 g/dL (P < or = 0.04 compared with end of IDPN phase), an increase in transferrin to 298 +/- 41 mg/dL (P = NS compared with end of IDPN phase), and an increase in IGF-1 to 212 +/- 45 ng/mL (P = 0.05 compared with end of IDPN phase).(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic glucagon sensitivity and fasting glucose concentration in normal dogs

We assessed hepatic glucagon sensitivity in overnight-fasted, conscious dogs. Six pancreatic replacement protocols were performed in each of five animals. Somatostatin was infused to inhibit endogenous insulin and glucagon, insulin was replaced intraportally at 200 microU.min-1.kg-1, and glucagon was infused intraportally at 0, 0.6, 1, 2, 5, or 20 ng.min-1.kg-1. One intravenous glucose tolerance test was also performed in each animal for measurement of insulin sensitivity (SI). During hormone replacement at a given glucagon dose, plasma glucose differed substantially among animals (P = 0.003). Therefore the dose required for restoration of euglycemia ("glucagon requirement") varied nearly sevenfold among animals, suggesting appreciable differences in glucagon sensitivity (GS). The latter was quantitated in individual animals as the initial slope of integrated glucose output vs. glucagon concentration. GS varied from 0.22 to 3.9 mg.kg-1.pg-1.ml among various animals and was inversely and significantly related to glucagon requirement. SI varied less (approximately 4-fold) and was not associated with glucagon requirement. These observations suggested that interanimal differences in glucose during hormone replacement were the result of substantial differences in GS. In addition, we found the GS of a given animal to be highly associated (P = 0.01) with its fasting glucose level. We conclude that GS varies substantially, and as such may be an important determinant of the fasting glucose level in normal animals.

Is hepatic glycogen content a regulator of glucagon secretion?

The role of plasma glucose as a major regulator of glucagon secretion is well established. However, this feedback regulation appears to break down in several states in which a closer relationship is apparently evident between plasma glucagon and hepatic glycogen content. Therefore, we assessed plasma glucagon as well as glucose response (delta glucose) to intravenous (IV) bolus administration of 1 mg glucagon after an overnight fast (a reliable and accurate estimate of the magnitude of hepatic glycogen content) in a population of normal subjects and subjects with hepatic cirrhosis and hyperthyroidism, both of which are disorders characterized by hepatic glycogen depletion. Plasma glucose concentrations were not significantly different in either group. However, plasma glucagon and insulin concentrations were significantly increased and delta glucose significantly decreased in both cirrhotic patients and hyperthyroid patients as compared with normal subjects. Furthermore, a significant relationship (r = -.55, P less than .0001) was noted between delta glucose and plasma glucagon, but not plasma insulin. Therefore, we believe that pancreatic alpha-cell function may be dependent on hepatic glycogen content. Moreover, the primary action of glucagon may be to induce gluconeogenesis in the absence of hepatic glycogen stores due to declining insulin concentrations or insulin resistance.

Carbohydrate metabolism in uremia

Abnormalities of insulin and glucose metabolism, namely glucose intolerance, inhibition of insulin secretion and insulin resistance, are present in children with chronic renal failure. Insulin resistance is universal among children with end-stage renal disease and may be caused by uremic toxins accumulated because of reduced renal function. The normal response of the beta cell is to enhance insulin secretion to overcome the insulin resistance. In patients with secondary hyperparathyroidism, this increase in insulin secretion is inhibited, resulting in glucose intolerance. Presence of glucose intolerance may be responsive for the growth retardation in uremic children. Improvements in glucose tolerance correlate with improvements in linear growth in uremic children. Further research should be directed towards investigation of the mechanisms by which abnormal energy utilization may affect growth in uremia and development of indices of glucose metabolism as predictors of growth in uremia.

Effects of portacaval shunt, transposition, and dimethylnitrosamine-induced chronic liver injury on pancreatic hormones and amino acids in dog

The effect of portacaval shunt on amino acid metabolism and pancreatic hormone secretion remains a subject of controversy. This might be due to the fact that shunt has two consequences; it shunts portal blood into the systemic circulation, and it causes hepatic parenchyma dysfunction by decreasing total hepatic blood flow. In order to see which one of these two is the more important factor, we created a model of portacaval transposition in dogs (PCT) causing portal systemic shunting without impairing hepatic blood flow and compared it with a model of hepatic dysfunction in dogs created by administering dimethylnitrosamine (DMNA). The dynamics of amino acid levels and pancreatic hormone secretion in the portal blood were investigated. DMNA dogs and dogs with a standard end-to-side portacaval shunt (Eck) showed elevated immunoreactive glucagon (IRG) levels and low immunoreactive insulin (IRI) levels in the portal blood as well as an amino acid imbalance, while values in PCT dogs were similar to those of controls. These data suggested that high IRG and low IRI in the portal blood and amino acid disturbances in the dogs with Eck shunts were due to hepatic parenchyma dysfunction, rather than to portal-systemic shunting.

Effect of glucagon on alcohol dehydrogenase activity in rat hepatocyte culture

The effect of glucagon on the activity of alcohol dehydrogenase in rat hepatocyte culture was determined. Glucagon concentrations of 0.1 nM enhanced, whereas concentrations greater than 1 nM decreased, alcohol dehydrogenase. These effects became apparent after exposure of the cultures to glucagon for 4 or more days. The presence of corticosterone (1 microM) prevented the enhancing effect of 0.1 nM glucagon on alcohol dehydrogenase activity. The changes in alcohol dehydrogenase caused by glucagon were associated with parallel changes in the rate of ethanol elimination. Alcohol dehydrogenase appears to be rate-limiting for ethanol oxidation, as uncoupling of oxidative phosphorylation did not modify the rate of ethanol elimination. These studies suggest a physiologic role of glucagon in enhancing liver alcohol dehydrogenase activity, whereas higher pharmacologic concentrations of glucagon have an opposite, depressant effect.

Long-term effects of nifedipine on carbohydrate and lipid metabolism in hypertensive hemodialyzed patients

To evaluate long-term effects of nifedipine on carbohydrate and lipid metabolism, 15 hypertensive patients undergoing regular hemodialysis treatment were investigated before nifedipine therapy, after 3 and 9 weeks, and 2 weeks after stopping nifedipine therapy. Three weeks following the administration of nifedipine, both glucose and insulin concentrations decreased significantly from 102.1 +/- 2.6 to 94.9 +/- 2.2 mg/dl and from 19.9 +/- 2.9 to 13.9 +/- 1.7 microU/ml and also remained significantly lower after 9 weeks of nifedipine therapy. This effect was paralleled by a fall of noradrenaline and dopamine. Glucagon levels remained constant. Glucose tolerance tests performed during nifedipine medication and 2 weeks after stopping of nifedipine therapy did not differ significantly. An increase of pyruvate, citric acid cycle intermediates, and ketone bodies--but not of lactate--was registered during nifedipine medication. The observed effects were not completely abolished after the 2-week placebo phase. Our data indicate that nifedipine lowers serum glucose values despite decreased insulin and constant glucagon levels in hypertensive hemodialyzed patients. Considering additionally the behavior of catecholamines and organic acids, the effects could be explained by the improvement of peripheral glucose utilization.

Beta-adrenergic contribution to glucagon-induced glucose production and insulin secretion in uremia

Spontaneous or propranolol-induced hypoglycemia can occur in uremic humans. We studied glucose kinetics (using [3-3H]glucose) in five uremic humans 24 h after hemodialysis and in seven normal controls. The effect of glucagon infusion at rates of 3, 6, 12, and 18 ng X kg-1 X min-1 at 60-min intervals was compared with either saline or beta-adrenergic blockade (propranolol infusion). In uremics, plasma glucose increased by 20-25% and by 40-50% at the 3 and 6 ng X kg-1 X min-1 glucagon doses, respectively, with no further increases at higher infusion rates. Glucose production increased transiently and in tandem with glucose uptake at each glucagon increment (P less than 0.0001). During beta-adrenergic blockade, the effect of glucagon in stimulating glucose production was blunted by 14-24% at the 6-18 ng X kg-1 X min-1 doses (P less than 0.05). During saline infusion, plasma insulin concentrations increased progressively to peak levels fourfold above basal at the 18 ng X kg-1 X min-1 dose. This increase in plasma insulin was virtually abolished by concomitant beta-adrenergic blockade (P = 0.0002). In contrast to uremic subjects, normal controls exhibited lesser degrees of hyperglycemia and hyperinsulinemia at all glucagon infusion rates. Propranolol infusion had no effect on the increments in glucose production and uptake nor on the plasma insulin response. These results suggest that in uremic humans propranolol independently reduces the hepatic response to glucagon and the insulin secretory response to hyperglycemia and/or hyperglucagonemia. These observations provide a possible mechanism for the adrenergic regulation of glucose homeostasis in uremia.

Effect of ammonia on glucagon secretion from the perfused pancreas of cirrhotic rats

Effects of ammonia on glucagon and insulin secretion from the perfused pancreas of cirrhotic rats were investigated to clarify the occurring mechanism of hypersecretion of pancreatic glucagon in liver cirrhotics. The results were as follows: During ammonia loading, insulin secretion was inhibited in a dose-related manner, whereas glucagon secretion was gradually increased at high concentrations of ammonia (2 mM) in control rats; this tendency was augmented in the presence of alpha-ketoglutarate in cirrhotic rats. On cessation of ammonia loading, a transient but definite increase in glucagon and insulin secretion was observed. Basal plasma glucagon and ammonia levels as well as basal glucagon secretion from the perfused pancreas of cirrhotic rats were significantly higher than in control rats. Basal insulin secretion from the perfused pancreas of cirrhotic rats was not different in spite of high levels of plasma insulin. Glucagon secretory response to glucose and arginine from the perfused pancreas of cirrhotic rats was higher than in the control pancreas, whereas insulin secretion was lower. In these cirrhotic rats, an increase in the number of islet cells, particularly A cells, was observed. These data suggested that hypersecretion of pancreatic glucagon which was responsible for hyperglucagonemia in cirrhotic rats might be attributed to high levels of ammonia and alpha-ketoglutarate in blood as well as to the fluctuation of abnormal ammonia concentration in blood and to the hypertrophy of islets, particularly of the A cell group due to hypersecretion.

Serum branched chain amino and keto acid response to fasting in humans

Eight healthy individuals were fasted for 72 hours. The concentrations of the branched chain keto acids (BCKA), branched chain amino acids (BCAA), C peptide, and glucagon were determined in peripheral venous blood. alpha-ketoisocaproic acid, alpha-keto-beta-methyl-n-valeric acid, and alpha-ketoisovaleric acid increased significantly within 36 hours along with the corresponding amino acids. After 60 hours of starvation, the concentrations of BCKA and BCAA declined despite the fact that the subjects were still in the fasting state. These changes were accompanied by a decrease in the concentrations of C peptide and an increase in glucagon levels. It is suggested that in starving man insulinopenia may contribute to the rise in BCKA concentrations and that the increase in BCKA may be a mechanism to reduce proteolysis.

Chronic renal failure: effect of hemodialysis on gastrointestinal hormones

Fifteen patients with chronic renal failure (serum creatinine level greater than 5 mg/dl) of long duration (more than 2 years) requiring hemodialysis were studied. Blood samples before and after 4 hours of hemodialysis were assayed for creatinine, blood urea nitrogen, potassium, calcium, glucose, insulin, gastrin, gastric inhibitory polypeptide, vasoactive intestinal polypeptide, pancreatic polypeptide, somatostatin, motilin, and neurotensin levels. Before dialysis, serum gastrin was minimally increased whereas gastric inhibitory polypeptide and pancreatic polypeptide were grossly increased compared with normal fasting values. Hemodialysis produced no changes in serum gastric inhibitory polypeptide, vasoactive intestinal polypeptide, pancreatic polypeptide, somatostatin, motilin, and neurotensin. Slight increases in serum insulin and gastrin levels may have occurred secondary to a dialysis-induced increase in the serum calcium level. The kidneys appear to be a major site of inactivation of insulin, gastrin, gastric inhibitory polypeptide, and pancreatic polypeptide. The gastrin level, although elevated in renal failure patients, may be suppressed by very high circulating levels of gastric inhibitory polypeptide.

Cardiovascular and metabolic responses to submaximal exercise in hemodialysis patients

Eight chronic hemodialysis (cHD) patients and six healthy sedentary controls (C) were exercised for 60 minutes at 52 +/- 8% (cHD patients) and 48 +/- 4% (C) of their maximal oxygen consumption levels. Plasma lactate levels at rest and during exercise were comparable in both groups. Respiratory exchange ratios were lower in cHD patients, but they increased during exercise to levels comparable to those of the C group. Despite comparable heart rates at rest, exercise of similar intensity led to lower heart rates at 30 and 60 minutes in cHD patients compared to C (P less than 0.05). The cHD patients had higher systolic and mean arterial pressures at rest than did C (P less than 0.05), but during exercise the increments in systolic and mean blood pressures were lower in cHD patients than they were in C (P less than 0.05). In spite of these blunted cardiovascular responses, plasma catecholamines increased during exercise in both groups. Plasma glucose levels were similar in both groups during exercise in spite of significantly higher plasma levels of insulin and glucagon in cHD patients throughout the exercise session (P less than 0.01). These data demonstrate that chronic cHD patients can exercise at a modest intensity for a prolonged period of time without untoward cardiovascular or metabolic responses. Their poor exercise response does not appear to be related to an inadequate activation of the sympathoadrenal system.