Glucagon metabolism in normal subjects and in cirrhotic patients before and after portasystemic venous shunt surgery

Eradicating hepatitis C virus ameliorates insulin resistance without change in adipose depots

Chronic hepatitis C (CHC) is associated with lipid-related changes and insulin resistance; the latter predicts response to antiviral therapy, liver disease progression and the risk of diabetes. We sought to determine whether insulin sensitivity improves following CHC viral eradication after antiviral therapy and whether this is accompanied by changes in fat depots or adipokine levels. We compared 8 normoglycaemic men with CHC (genotype 1 or 3) before and at least 6 months post viral eradication and 15 hepatitis C antibody negative controls using an intravenous glucose tolerance test and two-step hyperinsulinaemic-euglycaemic clamp with [6,6-(2) H2 ] glucose to assess peripheral and hepatic insulin sensitivity. Magnetic resonance imaging and spectroscopy quantified abdominal fat compartments, liver and intramyocellular lipid. Peripheral insulin sensitivity improved (glucose infusion rate during high-dose insulin increased from 10.1 ± 1.6 to 12 ± 2.1 mg/kg/min/, P = 0.025), with no change in hepatic insulin response following successful viral eradication, without any accompanying change in muscle, liver or abdominal fat depots. There was corresponding improvement in incremental glycaemic response to intravenous glucose (pretreatment: 62.1 ± 8.3 vs post-treatment: 56.1 ± 8.5 mm, P = 0.008). Insulin sensitivity after viral clearance was comparable to matched controls without CHC. Post therapy, liver enzyme levels decreased but, interestingly, levels of glucagon, fatty acid-binding protein and lipocalin-2 remained elevated. Eradication of the hepatitis C virus improves insulin sensitivity without alteration in fat depots, adipokine or glucagon levels, consistent with a direct link of the virus with insulin resistance.

Mechanisms of hyperinsulinemia and hyperglucagonemia after liver transplantation

These studies were undertaken to evaluate the mechanisms for changes in plasma insulin and glucagon levels observed post-liver transplantation. Two groups of pigs were studied: a control group (n = 8) underwent laparotomy and catheter placement in the carotid artery and portal and hepatic veins. Hepatic blood flow was measured by ultrasonic flow probes placed around the hepatic artery and portal vein. An experimental group (n = 8) underwent orthotopic liver transplantation and similar instrumentation. On Day 1 after surgery, an estimate of insulin and glucagon secretion and hepatic extraction was determined using arteriovenous difference techniques. Serum assays were performed for markers of hepatic and renal function. Plasma insulin levels of the transplanted pigs were higher in the carotid artery (4 +/- 1 microU/ml vs 7 +/- 1 microU/ml), but not in the hepatic vein (5 +/- 1 microU/ml vs 7 +/- 1 microU/ml) and in the portal vein (10 +/- 2 microU/ml vs 12 +/- 2 microU/ml). Arterial plasma C-peptide was significantly greater in the transplanted group (0.23 +/- 0.02 ng/ml vs 0.42 +/- 0.03 ng/ml); however, the molar ratio of C-peptide and insulin was not different between the two groups (3.6 +/- 0.9 vs 3.4 +/- 0.4). Plasma glucagon levels of the transplanted pigs were significantly elevated in the carotid artery (111 +/- 11 pg/ml vs 323 +/- 65 pg/ml), portal vein (221 +/- 27 pg/ml vs 495 +/- 69 pg/ml), and hepatic vein (142 +/- 15 pg/ml vs 395 +/- 58 pg/ml). The estimate of pancreatic secretion of insulin (115 +/- 28 microU/kg.min) vs 71 +/- 21 microU/kg.min) and glucagon (2.0 +/- 0.4 ng/kg.min vs 2.7 +/- 0.7 ng/kg.min) and the fractional hepatic extraction rate of insulin (35 +/- 8% vs 32 +/- 5%) were not different between the two groups. However, the hepatic fractional extraction rate of glucagon was significantly decreased in the transplanted group (25 +/- 5% vs 11 +/- 3%). Therefore, the hyperglucagonemia observed 24 hr following liver transplantation is partly due to reduced hepatic fractional extraction of glucagon while the hyperinsulinemia is mainly due to the nonhepatic clearance of insulin. We speculate that decreased renal function may contribute to the hyperinsulinemia, elevated C-peptide concentrations, and hyperglucagonemia.

Failure of glucagon to stimulate hepatic glycogenolysis in well-nourished patients with mild cirrhosis

The ability of glucagon to stimulate hepatic glucose production (HGP) was studied in clinically stable cirrhotic patients (n = 8) who had, based on long-term follow-up evaluation, relatively good liver function (Child-Pugh A) and whose dietary intake and physical characteristics were comparable to those of healthy control subjects (n = 8). Plasma glucagon concentration was slightly but not significantly increased in cirrhotic patients versus control subjects in the basal state (190 +/- 41 v 126 +/- 24 pg/mL, P = NS) and during a continuous 180-minute glucagon infusion at 3 ng/kg/min (349 +/- 56 v 243 +/- 37, P = NS). The increment in plasma glucagon level (+164 +/- 57 v +127 +/- 35, P = NS) also was slightly greater in the cirrhotic group. HGP (measured with [6-3H]-glucose) in the basal state was similar in cirrhotic and control subjects (1.79 +/- 0.09 v 1.94 +/- 0.15 mg/kg/min, P = NS). In cirrhotic patients, stimulation of HGP by glucagon was blunted during the first 15 to 30 minutes of the infusion period (representing glucagon's predominant effect on glycogenolysis; 0.23 +/- 0.20 v 1.06 +/- 0.19 mg/kg/min, P < .05), but it was not different from that in control subjects during the remaining course of the experiment (30 to 180 minutes). Basal plasma insulin and C-peptide concentrations did not change from baseline during the glucagon infusion in cirrhotics, whereas they increased slightly but not significantly in controls. These data demonstrate that even in the early stages of cirrhosis, the liver is resistant to the stimulatory effect of glucagon on hepatic glycogenolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Relationship of insulin resistance to protein-energy malnutrition in patients with alcoholic liver cirrhosis: effect of short-term nutritional support

Protein-energy malnutrition (PEM) and insulin resistance (IR) are common features of alcoholic liver cirrhosis (ALC). In order to determine a relationship between them, nutritional status and glucose homeostasis were studied in 26 patients with ALC. Nutritional status was assessed through dietary, anthropometric, and biological parameters. An IR index (M/I) was obtained from the euglycemic insulin clamp technique. M/I was significantly correlated with accurate markers of PEM (albumin, transthyretin, and retinol-binding protein) but not with other markers of liver dysfunction. Nine patients were studied before and after nutritional support: M/I was significantly improved as were serum markers of PEM. Other markers of liver dysfunction were also significantly improved. These findings suggest that PEM could be responsible, in part, for IR in patients with ALC who are frequently malnourished. Moreover, nutritional support improved insulin sensitivity in these patients.

Islet cell responses to glucose in human transplanted pancreas

Postsurgery, pancreas transplantation results in alterations of carbohydrate metabolism. Additionally, immunosuppressive therapy impacts on glucose regulation. We evaluated the hormonal and metabolic responses of pancreas allografts, utilizing the hyperglycemic clamp technique coupled with the tritiated glucose methodology, in 11 volunteers who had received simultaneous pancreas-kidney transplantation (P-K) with systemic drainage. Their responses were compared with seven volunteers who had received only a kidney (K) graft and with seven normal control (C) volunteers. Although basal glucose and hepatic glucose output were similar in all three groups, basal insulin, C-peptide, glucagon, and pancreatic polypeptide were highest in the P-K group and lowest in normal subjects. During hyperglycemia, all groups showed a similar characteristic, initial complete suppression of hepatic glucose production, with recovery followed by a later suppression. Peripheral glucose uptake was similar in P-K and C subjects but decreased in K patients. Systemic insulin levels were fourfold higher in the pancreas transplant patients than in healthy subjects. Thus, under basal and hyperglycemic stimulation, 1) hepatic glucose homeostasis is regulated normally, even with pancreatic drainage into the systemic circulation; 2) overall glucose disposal is normal in P-K patients because of marked hyperinsulinemia; and 3) there is loss of tonic inhibition of endocrine pancreatic function secondary to pancreatic denervation.

C-peptide in non-alcoholic cirrhosis and hepatocellular carcinoma

Fourteen normal controls, eleven patients with non-alcoholic cirrhosis, twenty-nine with hepatocellular carcinoma (HCC) and six with HCC and hypoglycemia were studied. The tests performed include iv glucose tolerance test (25 g) and glucagon challenge test (2 mg). In cirrhosis, glucose intolerance and insulin resistance were demonstrated. The fasting hyperinsulinemia in cirrhosis is the result of decreased degradation as shown by the normal fasting C-peptide. The increased insulin responses to glucose, despite a normal C-peptide response, further supports the importance of impaired degradation in the pathogenesis of hyperinsulinemia after challenge. Despite a strong etiological association between cirrhosis and HCC, patients with HCC do not have significant hyperinsulinemia or glucose intolerance. This provides metabolic evidence to support the clinico-pathological observation that HCC occurred when cirrhosis was not advanced or in a precirrhotic stage. In HCC patients with clinically overt hypoglycemia, the fasting glucose, insulin and C-peptide were very low. The C-peptide responses to glucose and glucagon challenges were suppressed despite pharmacologic stimulation. This can be explained by the suppression of insulin secretion by a circulating substance secreted by hepatoma. The results support the pathogenetic importance of insulin-like activities recently detected in HCC patients with hypoglycemia.

Elevated plasma ammonia level in hepatic cirrhosis: role of glucagon

Elevated plasma ammonia level in hepatic cirrhosis has been attributed to a lack of conversion of enteric ammonia into urea or to its entry into systemic circulation via portasystemic shunting, or to both. It is exaggerated by excessive protein intake. Because hyperglucagonemia is well documented in cirrhosis and a protein meal is an effective glucagon secretagogue, plasma glucose, insulin, glucagon, and ammonia levels were determined in 50 cirrhotic patients after an overnight fast. Effects of a protein meal were also assessed in 20 of these patients. Plasma glucose was normal and remained unaltered after a protein meal. Insulin, glucagon, and ammonia levels were elevated, but only in patients with advanced liver dysfunction. Ammonia levels correlated significantly with glucagon (r = 0.61, p less than 0.001), but not with insulin or glucose levels. Insulin and glucagon levels rose after a protein meal in all patients and controls; whereas a significant rise in the ammonia level occurred only in decompensated cirrhotics. Elevation of the ammonia level was significantly correlated with fasting glucagon (r = 0.54, p less than 0.05), as well as with glucagon response (r = 0.65, p less than 0.01), but not with basal insulin or insulin response. Furthermore, the rise in ammonia level occurred too early to be accounted for by enteric generation. Finally, direct effects of glucagon administration on plasma glucose and serum ammonia were examined in 15 cirrhotic patients. Glucose response was significantly blunted in cirrhotic patients as compared with normal subjects, whereas serum ammonia rose promptly but only in cirrhotics, with maximum rise being noted in cirrhotic patients with advanced liver dysfunction. This study, therefore, suggests that hyperglucagonemia may contribute significantly to hyperammonemia in hepatic cirrhosis.

Hyperinsulinaemia and insulin resistance of cirrhosis: the importance of insulin hypersecretion

The mechanism for the hyperinsulinaemia in cirrhosis was investigated using two different approaches. In the first study, the metabolic clearance rate of insulin was measured at steady state in 13 cirrhotic and 13 weight-matched control subjects. With comparable insulin infusion rates (1.00 +/- 0.19 versus 1.07 +/- 0.15 mU/kg/min), steady-state plasma insulin concentrations (104 +/- 25 versus 87 +/- 12 microU/ml; P greater than 0.5) and MCRIRI (13.6 +/- 1.6 versus 15.4 +/- 2.0 ml/kg/min; P greater than 0.5) were similar. In the second study, fasting and oral glucose stimulated C-peptide/insulin ratios were compared in 16 cirrhotic and 18 weight matched control subjects. Although fasting glucose levels were significantly higher in the cirrhotic groups, all values were in the normal range (5.5 +/- 0.3 versus 4.8 +/- 0.1 mmol/l, P less than 0.02). However, fasting insulin (0.171 +/- 0.02 versus 0.068 +/- 0.004 nmol/l) and C-peptide (1.02 +/- 0.13 versus 0.42 +/- 0.02 nmol/l) were strikingly higher (P less than 0.001) in cirrhotic subjects. On the other hand, fasting C-peptide/insulin ratios were not statistically different in the two groups (6.18 +/- 0.52 versus 6.77 +/- 0.46; P greater than 0.3). This suggests that beta cell hypersecretion was the principal cause of the fasting hyperinsulinaemia, rather than decreased insulin hepatic extraction. Following the glucose load in 13 of the control and seven of the cirrhotic group, the C-peptide/insulin ratio fell in both groups but was significantly lower in the cirrhotic compared to control subjects at 30, 60 and 120 min, consistent with possible impairment of hepatic insulin extraction.(ABSTRACT TRUNCATED AT 250 WORDS)