Effect of insulin on hepatic bile secretion during normoglycaemia and hyperglycaemia

Dynamics and determinants of human plasma bile acid profiles during dietary challenges

In recent years, bile acids (BA) have received great interest due to their pleiotropic biological activity and the presence of plasma membrane-bound and nuclear receptors. Moreover, BA in blood have been identified by metabolite screening approaches as biomarkers that are associated with various diseases and even with a human longevity phenotype. With the growing interest in the microbiota contribution to the health-disease trajectory, BA that undergo deconjugation and other modifications by bacteria in the large intestine have become a prime target as a microbiome diversity modifier. We here profiled BA by a quantitative and a semiquantitative approach in 15 healthy and phenotypically very similar young individuals for over a 36-h fasting period, an oral glucose tolerance test (OGTT), and an oral lipid tolerance test (OLTT). We demonstrate a remarkable heterogeneity of the responses and describe the different dynamics of the plasma changes that likely originate from different routes by which BA enters the peripheral blood, and that may represent a direct secretion from the liver into the blood and a route that reaches the blood as a spill-over after passing from the gallbladder through the intestine and the portal system. We discuss the finding that an individual transport process involved in the passage of BA could be a critical determinant in the kinetics of plasma appearance and the overall phenotypic variability found.

Macronutrients and insulin resistance in cholesterol gallstone disease

Cholelithiasis is a major source of digestive morbidity worldwide. Cholesterol stones account for the majority of gallstones in the United States and other Western countries. The pathogenesis of cholesterol gallstone disease is multifactorial with key factors including cholesterol supersaturation of bile, altered biliary motility, and nucleation and growth of cholesterol crystals. Increasing evidence suggests that many, but not all, causative factors of cholesterol gallstones are related to insulin resistance which, in association with obesity, has reached an epidemic level worldwide. Experimental studies show that hyperinsulinemia, a key feature of insulin resistance, may cause increased hepatic cholesterol secretion and cholesterol supersaturation of bile and gallbladder dysmotility, and thereby may enhance gallstone formation. Insulin resistance syndrome can be modified by environmental factors, including dietary factors. The impact of diet on insulin sensitivity is mediated by both dietary composition and its energy content. The contribution of specific dietary elements to the prevalence and incidence of cholesterol gallstone disease has been explored in animal and human studies. There is considerable evidence to suggest that different types of fatty acids, independent of the total amount of fat consumption, affect insulin sensitivity and cholesterol gallstone disease differently. The effects of salt intake, consumption of protein and carbohydrates, and alcohol drinking on insulin resistance are controversial. Additional intervention trials and controlled experimental feeding studies are needed to further clarify these relationships and to provide useful prophylactic and therapeutic strategies.

Effect of insulin on basal and cholecystokinin-stimulated gallbladder motility in humans

BACKGROUND/AIMS

Acute hyperglycemia inhibits gallbladder contraction. In non-diabetic subjects this inhibitory effect may result from endogenous hyperinsulinemia. Therefore we investigated the effects of acute hyperglycemia and euglycemic hyperinsulinemia on basal and cholecystokinin-stimulated gallbladder motility.

METHODS

Gallbladder volume (ultrasonography) and duodenal bilirubin output were studied simultaneously in nine healthy volunteers (age 20-52 years) on 3 separate occasions in random order during: (a) saline infusion (control), (b) hyperglycemic hyperinsulinemic clamping (HG; plasma glucose at 15 mmol/l), and (c) euglycemic hyperinsulinemic clamping (HI; plasma insulin at 150 mU/l, glucose at 4-5 mmol/l). After a 2-h basal clamp period, cholecystokinin was infused intravenously for 60 min at 0.25 IDU x kg(-1) x h(-1), followed by another 60 min at 0.5 IDU x kg(-1) x h(-1).

RESULTS

HI and HG significantly (p<0.05) reduced basal duodenal bilirubin output compared to control, while basal gallbladder volume did not change. At the low dose cholecystokinin, gallbladder emptying during HG (25+/-3%) and HI (39+/-4%) was significantly (p<0.01) reduced compared to control (61+/-4%). The inhibitory effect of HG was significantly (p<0.05) stronger compared to HI. Duodenal bilirubin output during the low dose cholecystokinin was significantly (p<0.05) reduced by HG, but not by HI. No inhibitory effect of HG and HI on gallbladder emptying and duodenal bilirubin output was observed with the high dose of cholecystokinin.

CONCLUSIONS

In healthy subjects acute hyperglycemia and euglycemic hyperinsulinemia reduce basal duodenal bilirubin output and inhibit gallbladder emptying stimulated by low dose cholecystokinin. These results suggest that insulin is involved in the inhibitory effect of hyperglycemia on basal and cholecystokinin-stimulated gallbladder motility.