Metabolic responses to monocomponent human insulin infusions in normal subjects and patients with liver and endocrine disease

Differences in circulating appetite-related hormone concentrations between younger and older adults: a systematic review and meta-analysis

Ageing is associated with reduced appetite and energy intakes. However, the mechanisms underlying this phenomenon are not fully understood. This systematic review and meta-analysis quantified differences in circulating concentrations of appetite-related hormones between healthy older and younger adults. Six databases were searched through 12th June 2018 for studies that compared appetite-related hormone concentrations between older and younger adults. Data were pooled using random-effects meta-analysis and are presented as standardised mean difference (Hedges’ g) with 95% confidence intervals (95% CI). Thirty-five studies were included involving 710 older adults (mean ± SD; age: 73 ± 5 years) and 713 younger adults (age: 28 ± 7 years). Compared with younger adults, older adults exhibited higher fasted and postprandial concentrations of the anorectic hormones cholecystokinin (Fasted: SMD 0.41 (95% CI 0.24, 0.57); p < 0.001. Postprandial: SMD 0.41 (0.20, 0.62); p < 0.001), leptin [Fasted: SMD 1.23 (0.15, 2.30); p = 0.025. Postprandial: SMD 0.62 (0.23, 1.01); p = 0.002] and insulin [Fasted: SMD 0.24 (− 0.02, 0.50); p = 0.073. Postprandial: SMD 0.16 (0.01, 0.32); p = 0.043]. Higher postprandial concentrations of peptide-YY were also observed in older adults compared with younger adults [SMD 0.31 (− 0.03, 0.65); p = 0.075]. Compared with younger adults, older adults had lower energy intakes [SMD − 0.98 (− 1.74, − 0.22); p = 0.011], and lower hunger perceptions in the fasted [SMD − 1.00 (− 1.54, − 0.46); p < 0.001] and postprandial states [SMD − 0.31, (− 0.64, 0.02); p = 0.064]. Higher circulating concentrations of insulin, leptin, cholecystokinin and peptide-YY accord with reduced appetite and energy intakes in healthy older adults. Interventions to reduce circulating levels of these hormones may be beneficial for combatting the anorexia of ageing.

Role of meal carbohydrate content for the imbalance of plasma amino acids in patients with liver cirrhosis

BACKGROUND AND AIM

Imbalance of circulating branched chain amino acids (BCAA) versus aromatic amino acids (AAA) and hyperinsulinemia are common metabolic alterations in patients with liver cirrhosis. The aim of this study was to characterize the effect of the carbohydrate component of a protein-rich mixed meal on postprandial plasma concentrations of 21 amino acids, insulin and C-peptide in patients with compensated liver cirrhosis. Furthermore, the effect of a dietary intervention on the metabolic alterations in cirrhotic patients was examined.

METHODS

Eighteen patients with cirrhosis and 12 healthy volunteers received a protein-rich meal (pork filet 200 g) with or without carbohydrates (bread 50 g, glucose 20 g). A subgroup of four cirrhotic patients received an isoenergetic (117 kJ/kg bw) carbohydrate-enriched (60%) and -restricted (20%) diet for 7 days each.

RESULTS

In the cirrhotic patients, basal plasma insulin and C-peptide concentrations were significantly elevated. The ingestion of a protein-rich meal without additional carbohydrates led to a significantly greater increase of insulin and C-peptide in the cirrhotic patients compared to controls. Postprandial increases of leucine and isoleucine were reduced, whereas those of phenylalanine were higher in cirrhotic patients. The addition of carbohydrates led to higher insulin and C-peptide plasma concentrations in cirrhotic patients. Postprandial BCAA increases were more impaired in the cirrhotic group after additional carbohydrate ingestion (46%vs 82%). After the carbohydrate-restricted diet for 7 days BCAA plasma levels increased but the BCAA/AAA ratio remained unaltered.

CONCLUSIONS

The carbohydrate content of a meal enhances reduction of BCAA plasma concentrations in clinically stable cirrhotic patients. An imbalanced BCAA/AAA ratio cannot be avoided by a carbohydrate-reduced diet alone, supporting mandatory BCAA supplementation.

Attenuated peptide YY release in obese subjects is associated with reduced satiety

The responses of the gut hormone peptide YY (PYY) to food were investigated in 20 normal-weight and 20 obese humans in response to six test meals of varying calorie content. Human volunteers had a graded rise in plasma PYY (R2 = 0.96; P < 0.001) during increasing calorific meals, but the obese subjects had a lower endogenous PYY response at each meal size (P < 0.05 at all levels). The ratio of plasma PYY(1-36) to PYY(3-36) was similar in normal-weight and obese subjects. The effect on food intake and satiety of graded doses of exogenous PYY(3-36) was also evaluated in 12 human volunteers. Stepwise increasing doses of exogenous PYY(3-36) in humans caused a graded reduction in food intake (R2 = 0.38; P < 0.001). In high-fat-fed (HF) mice that became obese and low-fat-fed mice that remained normal weight, we measured plasma PYY, tissue PYY, and PYY mRNA levels and assessed the effect of exogenous administered PYY(3-36) on food intake in HF mice. HF mice remained sensitive to the anorectic effects of exogenous ip PYY(3-36). Compared with low-fat-fed fed mice, the HF mice had lower endogenous plasma PYY and higher tissue PYY but similar PYY mRNA levels, suggesting a possible reduction of PYY release. Thus, fasting and postprandial endogenous plasma PYY levels were attenuated in obese humans and rodents. The PYY(3-36) infusion study showed that the degree of plasma PYY reduction in obese subjects were likely associated with decreased satiety and relatively increased food intake. We conclude that obese subjects have a PYY deficiency that would reduce satiety and could thus reinforce their obesity.

Insulin resistance in cirrhosis: evidence for a post-receptor defect

Receptor and post-receptor abnormalities of insulin action and their possible role in the insulin resistance of cirrhosis were examined in eight biopsy-proven cirrhotic subjects and eight age-weight matched healthy volunteers. To this end, oral glucose tolerance tests (OGTT), insulin dose response curves and insulin binding to circulating monocytes were determined for each subject. The dose-response curves for the cirrhotic subjects were significantly shifted to the right compared to the control subjects, indicating the presence of insulin insensitivity (ED50 223 +/- 30 versus 64 +/- 8 mU/l respectively; P less than 0.001). The magnitude of the right shift of the insulin-dose response curves correlated significantly (P less than 0.001) with the OGTT 2 h insulin levels (r = 0.74) and the insulin areas under the OGTT curves (r = 0.86). In contrast, insulin responsiveness was marginally elevated in the cirrhotic group (maximal glucose disposal 680 +/- 47 versus 574 +/- 21 ml/m2/min; P less than 0.05). Insulin binding to circulating monocytes was normal in the cirrhotic subjects. It is concluded that the insulin resistance of cirrhosis is due to a post-receptor defect in insulin action which reduces insulin sensitivity but not insulin responsiveness.

Decreased insulin receptor binding in hyperthyroidism

The binding of 125I-insulin to insulin receptors on circulating mononuclear leukocytes was studied in ten patients with hyperthyroidism and 20 euthyroid normal volunteers. The hyperthyroid patients demonstrated significantly elevated glucose levels following an oral glucose load, despite normal insulin secretion. The infusion of insulin resulted in a delayed hypoglycaemic effect in the hyperthyroid patients; however, the inhibition of the endogenous insulin secretion as indicated by suppression of C-peptide levels was not different from euthyroid control subjects. Insulin binding to monocytes was significantly decreased in the hyperthyroid patients. Scatchard analysis of binding data indicates that a decrease of receptor number rather than receptor affinity seems to be the cause of the lowered insulin binding in hyperthyroid patients with diffuse toxic goitre. The findings of decreased insulin receptor number, mild degree of glucose intolerance despite normal insulin secretion and the delayed hypoglycaemic effect following insulin infusion suggest that peripheral insulin resistance could be involved in the highly complex pathophysiology of glucose intolerance in hyperthyroidism.

Hormone and metabolite profiles in alcoholic liver disease

Circulating hormone and metabolite profiles have been studied in ten patients with alcoholic cirrhosis, five patients with alcoholic hepatitis and/or fatty liver, and nine normal controls over a 12-h period of meals and activity. Blood glucose was elevated throughout the day in both cirrhotic and non-cirrhotic alcoholics (mean 12-h glucose; controls 5.38 +/- 0.16 (SEM) mmol/l; cirrhotics 6.98 +/- 0.30 mmol/l, P less than 0.001; non-cirrhotics 7.18 +/- 0.26 mmol/l, P less than 0.001). Non-cirrhotic alcoholics had an exaggerated insulin response to meals, whereas cirrhotic patients had hyperinsulinaemia throughout the day (mean 12-h insulin; controls 16.3 +/- 2.3 mU/l; cirrhotics 35.8 +/- 6.6 mU/l, P less than 0.02). Growth hormone levels were elevated only in patients with cirrhosis (mean 12-h growth hormone, 7.06 +/- 1.35 v. 0.85 +/- 0.17 micrograms/l, P less than 0.001). Serum cortisol was persistently elevated in cirrhotics but only in the evening in non-cirrhotic alcoholics. Lactate and pyruvate responses to meals were exaggerated in non-cirrhotic patients whereas in cirrhotics, levels were persistently raised. Blood glycerol was elevated in all alcoholic patients whereas ketone body levels were normal. Hypertriglyceridaemia was observed only in non-cirrhotic patients. No relationship between the endocrine and metabolic state was observed in either cirrhotic or non-cirrhotic patients.

Glucose metabolism by isolated fat cells from sloth

Glucose metabolism by sloth fat cells with and without addition of insulin was investigated. The data were compared to the results obtained with rat fat cells incubated under the same experimental conditions. Sloth fat cells showed a very low glucose oxidation to 14CO2 and incorporation into total lipids. The glucose incorporated into lipids is mainly in the glyceride-glycerol moiety. Addition of insulin did not produce an increase on glucose oxidation and a slight increase in the incorporation into total lipids was observed. Since it has been reported that sloths have a very low rate on thyroxine secretion, the results are discussed in relation to data in the literature on carbohydrate and lipid metabolism in hypothyroid animals.

Relationship between body fat mass, carbohydrate tolerance and IRI response during glucose infusion in subjects with early diabetes

We have studied the interrelationship of total body fat mass, carbohydrate tolerance and IRI response in 17 non-obese and obese subjects, who were suspected of having early diabetes. We carried out an i.v. glucose infusion test consisting of a priming injection of 0.33 g/kg followed by constant glucose infusion of 12 mg/kg/min in all persons. Total body fat mass was estimated by the tritium dilution method. There was a positive correlation of body fat mass, fasting glucose concentration and blood glucose concentration at 150 min as well as a strong correlation between body fat mass and BG area 60--120 min as parameters of carbohydrate tolerance in all subjects, i.e. the degree of carbohyrate intolerance was directly related to the quantity of total body fat mass. A similar correlation was found when the non-obese and obese groups were analyzed separately. In neither group did total body fat mass correlate with parameters of IRI response. In obese subjects with pathological carbohydrate tolerance, however, a positive correlation of basal IRI concentration and total body fat mass was found. Furthermore, a close relation between basal IRI level and parameters of carbohydrate tolerance could be demonstrated in obese subjects. The present study failed to demonstrate any correlation of parameters of carbohydrate tolerance and glucose-induced IRI response in either group. Thus, the significant relationship between body fat mass and degree of carbohydrate intolerance indicates that body fat mass plays an important role in the disturbance of blood glucose homeostasis in early diabetes with and without obesity.

Is the growth-hormone response to insulin due to hypoglycaemia, hyperinsulinaemia or a fall in plasma free fatty acids?

Seven normal male volunteers were given a 2 h intravenous infusion of insulin (2 mu kg-1 min-1). During the first hour, in which nomoglycaemia was maintained by glucose infusion, no detectable increase in growth hormone (GH) secretion occurred. When controlled symptomatic hypoglycaemia was produced during the second hour of the insulin infusion a brisk rise in plasma GH concentration was observed in all the subjects studied. Since it was possible that the falls in the concentration of plasma free fatty acids (FFA) occurring during infusion of insulin also acted as a stimulus to GH release the study was repeated in four subjects but normoglycaemia was maintained throughout the entire 2 h period of insulin infusion. In these experiments there was no rise in plasma GH concentration although a similar fall in plasma FFA was produced. These results clearly indicate that hypoglycaemia per se was the important stimulus to GH secretion and not hyperinsulinaemia or a lowering of plasma FFA. Furthermore there appeared to be a threshold hypoglycaemic stimulus to GH secretion. In no subject was a rise in plasma GH seen without a fall in plasma glucose greater than 1.4 mmol/l. Prolonged mild hypoglycaemia did not stimulate GH secretion.

Effects of thyroid hormone deficiency on the distribution of hepatic metabolites and control of pathways of carbohydrate metabolism in liver and adipose tissue of the rat

1. Measurements have been made of the hepatic metabolites in normal and thyroidectomized rats and enzymes of the glycolytic route, the pentose phosphate pathway, the tricarboxylic acid cycle and lipogenesis together with the flux of glucose through alternative pathways of glucose metabolism and into lipid. 2. There is a significant fall in the content of ADP, AMP, citrate, long-chain acyl-CoA derivatives and a rise of 3-phosphoglycerate, 2-phosphoglycerate and phosphoenolpyruvate following thyroidectomy. The observed changes in the glycolytic intermediates may be correlated with the increased activity of phosphofructokinase relative to pyruvate kinase and fructose bisphosphatase. 3. The NAD+/NADH quotient of the mitochondrial compartment, calculated from the reactants and Keq of 3-hydroxybutyrate dehydrogenase, becomes significantly more oxidized in hypothyroid animals. The redox state of the cytosolic NAD and NADP couples remains relatively unchanged. 4. The changes in the hepatic content of CoA derivatives and citrate and in the mitochondrial redox state are interpreted as indicating a depressed rate of lipid oxidation. 5. Calculations of the compartmentation of metabolites between the cytosol and mitochondria indicate a very marked decrease in mitochondrial citrate, 2-oxoglutarate and glutamate with smaller changes in aspartate and malate. These changes are interpreted as providing evidence for the importance of modifications in the malate-aspartate shuttle in hypothyroidism; this is further supported by measured changes in the distribution and activities of the component enzymes of the hydrogen shuttles. 6. There is a diminished activity of glucokinase and of enzymes of the glycolytic pathway below phosphofructokinase in livers from hypothyroid rats. The oxidative enzymes of the pentose phosphate pathway, ATP-citrate lyase, 'malic' enzyme and fatty acid synthetase also decrease markedly. There is a striking parallelism between the changes of enzyme profile of liver and adipose tissue in hypothyroidism. 7. Adrenal glands from hypothyroid rats showed a generalized delcine in enzyme activity in parallel with the fall in tissue weight. Cytosolic glycerol-3-phosphate dehydrogenase decreased sharply. 8. The present results are discussed in relation to data in the literature on the increased activities of cyclic AMP and cyclic GMP phosphodiesterases in hypothyroidism, observations which integrate the relationships between anabolic and catabolic pathways of carbohydrate and lipid metabolism with alterations in hormone sensitivity in hypothyroidism.