Effect of pancreatic glucagon and its 1-21 fragment on gastric emptying in man

The acute effect of glucagon on components of energy balance and glucose homoeostasis in adults without diabetes: a systematic review and meta-analysis

Objective

Using a systematic review and meta-analysis, we aimed to estimate the mean effect of acute glucagon administration on components of energy balance and glucose homoeostasis in adults without diabetes.

Methods

CENTRAL, CINAHL, Embase, MEDLINE, PubMed, and Scopus databases were searched from inception to May 2021. To be included, papers had to be a randomised, crossover, single- or double-blind study, measuring ad libitum meal energy intake, energy expenditure, subjective appetite, glucose, and/or insulin following acute administration of glucagon and an appropriate comparator in adults without diabetes. Risk of bias was assessed using the Revised Cochrane Risk of Bias Tool for Randomized trials with additional considerations for cross-over trials. Certainty of evidence was assessed using the GRADE approach. Random-effect meta-analyses were performed for outcomes with at least five studies. This study is registered on PROSPERO (CRD42021269623).

Results

In total, 13 papers (15 studies) were considered eligible: energy intake (5 studies, 77 participants); energy expenditure (5 studies, 59 participants); subjective appetite (3 studies, 39 participants); glucose (13 studies, 159 participants); insulin (12 studies, 147 participants). All studies had some concerns with regards to risk of bias. Mean intervention effect of acute glucagon administration on energy intake was small (standardised mean difference [SMD]: –0.19; 95% CI, –0.59 to 0.21; P = 0.345). Mean intervention effect of acute glucagon administration on energy expenditure (SMD: 0.72; 95% CI, 0.37–1.08; P < 0.001), glucose (SMD: 1.11; 95% CI, 0.60–1.62; P < 0.001), and insulin (SMD: 1.33; 95% CI, 0.88–1.77; P < 0.001) was moderate to large.

Conclusions

Acute glucagon administration produces substantial increases in energy expenditure, and in circulating insulin and glucose concentrations. However, the effect of acute glucagon administration on energy intake is unclear. Insufficient evidence was available to evaluate the acute effect of glucagon on subjective appetite.

Glucose homeostasis and the gastrointestinal tract: insights into the treatment of diabetes

The gastrointestinal tract is increasingly viewed as a critical organ in glucose metabolism because of its role in delivering glucose to the circulation and in secreting multiple glucoregulatory hormones that, in concert with insulin and glucagon, regulate glucose homeostasis. Under normal conditions, a complex interplay of these hormones acts to maintain plasma glucose within a narrow range despite large variations in the availability of glucose, particularly during transition from the fasting to fed state. In the fed state, the rate at which nutrients are passed from the stomach to the duodenum, termed gastric emptying rate, is a key determinant of postprandial glucose flux. In patients with diabetes, the regulation of glucose metabolism is disrupted resulting in fasting and postprandial hyperglycaemia. Elucidation of the role of the gastrointestinal tract, gut-derived glucoregulatory peptides and gastric emptying rate offers a new perspective on glucose homeostasis and the respective importance of these factors in the diabetes state. This review will highlight the importance of the gastrointestinal tract in playing a key role in glucose homeostasis, particularly in the postprandial period, and the role of established or new therapies that either leverage or modify gastrointestinal function to improve glycaemic state.

Effects of glucagon on postprandial carbohydrate metabolism in nondiabetic humans

The present experiments sought to determine whether glucagon concentrations mimicking those observed in people with diabetes mellitus alter postprandial carbohydrate metabolism in nondiabetic humans. We measured the gastric emptying of solids and liquids, the systemic rate of appearance of ingested glucose, and endogenous glucose production either when postprandial suppression of glucagon was prevented by infusing glucagon at a rate of 0.65 ng/kg/min, when postprandial glucagon concentrations were elevated by infusing glucagon at a rate of 3.0 ng/kg/min, or when postprandial suppression of glucagon was permitted by infusion of saline. Despite marked differences in glucagon concentrations, postprandial glucose and insulin concentrations did not differ on any occasion. Although gastric emptying of liquids and solids was comparable on all three occasions, the high-dose, but not the low-dose, glucagon infusion caused a slight delay in the systemic appearance of ingested glucose and a significant decrease (P < .01) in postprandial D-xylose concentrations, suggesting a delay in carbohydrate absorption. However, this was offset by an increase (P < .05) in endogenous glucose production, resulting in no difference in postprandial glucose appearance. We conclude that in the absence of insulin deficiency, neither a lack of suppression of glucagon nor an elevation of glucagon to levels encountered in uncontrolled diabetes mellitus cause postprandial hyperglycemia in nondiabetic humans.

Mechanism of accelerated gastric emptying of liquids and hyperglycemia in patients with type II diabetes mellitus

BACKGROUND & AIMS

The roles of hyperglycemia in diabetic gastroparesis and gastric delivery in postprandial hyperglycemia of diabetic patients are unclear. The aims of this study were to assess gastric emptying and its relation to postprandial glucose metabolism in patients with asymptomatic non-insulin-dependent diabetes mellitus (NIDDM) and no autonomic neuropathy and to identify motor mechanisms responsible for any accelerated gastric emptying.

METHODS

Autonomic function, gastric emptying, postprandial glucose metabolism, and hormone levels (glucagon, insulin, cholecystokinin, glucose-dependent insulinotropic polypeptide, neurotensin, and peptide YY) were assessed in healthy volunteers and patients with NIDDM. In a second study, gastric tone and motility were measured in patients with accelerated gastric emptying and in controls.

RESULTS

Gastric emptying of solids did not differ in the two groups, but liquids emptied faster in patients with NIDDM (P < 0.02). The rate of entry of ingested glucose into the systemic circulation was similar, but higher postprandial glucagon and lower insulin concentrations led to greater (P < 0.01) postprandial hepatic glucose release. Levels of other enteropeptides, gastric accommodation, and antral motility were similar, but patients with NIDDM had greater proximal gastric phasic contractions than controls (P < 0.05).

CONCLUSIONS

Excessive hepatic glucose release, not rapid entry of ingested glucose, is the primary cause of postprandial hyperglycemia in patients with NIDDM. Accelerated gastric emptying in patients with nonneuropathic NIDDM is associated with increased proximal stomach phasic contractions.

Truncated GLP-1 (proglucagon 78-107-amide) inhibits gastric and pancreatic functions in man

We studied the effect of intravenous infusion of synthetic truncated GLP-1 (proglucagon 78-107-amide) on fasting and postprandial gastric acid secretion, gastric emptying, and pancreatic secretion of trypsin and lipase in eight normal volunteers using marker dilution and aspiration technique. The infusion resulted in a plasma concentration of 110 +/- 14 pmol/liter (mean +/- SEM). Truncated GLP-1 significantly inhibited postprandial acid secretion by 43 +/- 11% in spite of unchanged plasma gastrin concentration. Gastric emptying rate decreased significantly; 50% emptying time increased from 16 +/- 2 min to 30 +/- 5 min. Postprandial trypsin and lipase outputs were significantly inhibited by 47 +/- 17% and 40 +/- 9% during truncated GLP-1 infusion. Pancreatic enzyme output was linearly correlated to gastric emptying, and truncated GLP-1 did not affect this relationship, suggesting that the effect on pancreatic secretion was secondary to the effect on gastric emptying. Postprandial insulin and glucagon concentrations were similar with and without truncated GLP-1 infusion in spite of significantly lower blood glucose levels (5.2 +/- 0.2 versus 3.7 +/- 0.3), indicating that GLP-1 stimulated insulin secretion and inhibited glucagon secretion. In conclusion, our results suggest that truncated GLP-1 act as a physiological inhibitor of gastric and pancreatic functions in man.

Oxyntomodulin from distal gut. Role in regulation of gastric and pancreatic functions

We studied the effects of intravenous infusion of synthetic oxyntomodulin (proglucagon 33-69), a potential hormone from the ileal mucosa, on fasting and postprandial gastric acid secretion, gastric emptying, gastroduodenal motility, and pancreatic secretion of trypsin and lipase measured simultaneously in six normal volunteers using multilumen tubes for infusion of markers, manometry, and aspiration of gastric and duodenal contents. The infusion resulted in plasma concentrations of 203 +/- 21 pmol/liter (mean +/- SEM) of oxyntomodulin, regarded as high but not unphysiological concentrations of the peptide. Oxyntomodulin almost abolished basal acid secretion and inhibited postprandial acid secretion by 35 +/- 10%. Gastric emptying decreased significantly; the time for 50% to leave the stomach increased from 17.3 +/- 2.2 min to 34.7 +/- 8.0 min. The postprandial gastroduodenal motility was massively inhibited by oxyntomodulin. Postprandial trypsin and lipase output was significantly inhibited by 56 +/- 12% and 42 +/- 11%, respectively, during oxyntomodulin infusion. However, pancreatic enzyme output was linearly related to gastric emptying and oxyntomodulin did not influence this relationship, suggesting that oxyntomodulins effect was due to its effect on gastric emptying. Oxyntomodulin seems to play an important role in the small intestinal inhibitory control of gastropancreatic functions.