Intraventricular CCK-8 reduces single meal size in the baboon by interaction with type-A CCK receptors

Interactions between the central nervous system and pancreatic islet secretions: a historical perspective

The endocrine pancreas is richly innervated with sympathetic and parasympathetic projections from the brain. In the mid-20th century, it was established that α-adrenergic activation inhibits, whereas cholinergic stimulation promotes, insulin secretion; this demonstrated the importance of the sympathetic and parasympathetic systems in pancreatic endocrine function. It was later established that insulin injected peripherally could act within the brain, leading to the discovery of insulin and insulin receptors within the brain and the receptor-mediated transport of insulin into the central nervous system from endothelial cells. The insulin receptor within the central nervous system is widely distributed, reflecting insulin's diverse range of actions, including acting as an adiposity signal to reduce food intake and increase energy expenditure, regulation of systemic glucose responses, altering sympathetic activity, and involvement in cognitive function. As observed with central insulin administration, the pancreatic hormones glucagon, somatostatin, pancreatic polypeptide, and amylin can each also reduce food intake. Pancreatic and also gut hormones are released cephalically, in what is an important mechanism to prepare the body for a meal and prevent excessive postprandial hyperglycemia.

Appetite control and gastrointestinal hormonal behavior (CCK, GLP-1, PYY 1-36) following low doses of a whey protein-rich nutraceutic

Whey proteins represent the most satiating nutrients. In particular, their effects are due to enterohormonal changes (CCK, GLP-1 and PYY 1–36) observed after their exclusive ingestion. Glucomannan has important satiety property due to volume increase following gelification. The aim of the study is the evaluation of subjective rate of hunger and enterohormone concentrations (CCK, GLP-1, PYY 1–36) following oral loading of a mixture containing WP (8 g) or casein (8 g) plus glucomannan (1 g) (Colordiet^®, Inpha DUEMILA Srl Lecco, Italy). The study was conducted as a double-blind crossover with five healthy volunteers (BMI 22–26 kg/m² aging 18–65 years) in acute and a wash-out period of 1 week between the first and the second evaluation. From the analysis of the data, we observe that the load with WP induces a significant decrease in the desire to eat after 90 min (P < 0.0446) when compared with casein. As far as plasma hormones are concerned, there was a significant increase only in GLP-1 at 90 min after WP (P < 0.00166) and 180 min after casein (T0 vs. T180 P = 0.000129). There is a significant correlation between the increase in GLP-1 and decrease of desire to eat (R = −0.93). There is a tendency to the increasing of CCK after 90 min, which is not significant (P = 0.091). These results could be due to (a) the low number of cases or (b) the low dose of protein used. The present study suggests that a mixture of WP plus glucomannan exerts a decrease in the desire to eat which is correlated to enterohormonal modification (GLP-1 increase) despite the low content of protein (8 g) and the presence of glucomannan, which could reduce the fast absorption of WP in relation to the net forming during the gelification of the gastric environment.

Meal-anticipatory glucagon-like peptide-1 secretion in rats

Animals anticipating a meal initiate a series of responses enabling them to better cope with the meal's metabolic impact. These responses, such as cephalic insulin, occur prior to the onset of ingestion and are especially evident in animals maintained on a meal-feeding schedule with limited but predictable access to food each day. We tested the hypothesis that meal-fed rats secrete the incretin hormone glucagon-like peptide-1 (GLP-1) cephalically when anticipating a large meal. Male Long-Evans rats were fed ad libitum (controls) or adapted to a schedule on which food was available for the same 4-h period each day (meal fed animals). Plasma GLP-1 increased in meal-fed rats over an interval from 75 to 60 min prior to feeding time, from a baseline of 10 to around 40 pm, and then returned to baseline prior to food presentation. Controls had steady plasma GLP-1 levels (10-15 pm) over the same span. Meal-fed rats also secreted cephalic insulin starting around 15 min prior to food presentation. Administration of the selective GLP-1 receptor antagonist exendin-4[desHis-1,Glu-9] prior to the premeal spike of GLP-1 caused meal-fed rats to eat significantly less food than normal, whereas administration of the antagonist after the GLP-1 spike but prior to food presentation resulted in a significant increase in food consumption. These findings document for the first time a cephalic increase of plasma GLP-1 and suggest that it functions to facilitate consumption of a large meal.

Insulin and leptin: dual adiposity signals to the brain for the regulation of food intake and body weight

Insulin and leptin are hypothesized to be 'adiposity signals' for the long-term regulation of body weight by the brain. Accordingly, a change in the plasma levels of leptin or insulin indicates a state of altered energy homeostasis and adiposity, and the brain responds by adjusting food intake to restore adipose tissue mass to a regulated level. The candidate site for the brain's detection of leptin adiposity signaling is the hypothalamic arcuate nucleus, where leptin inhibits expression neuropeptide Y and increases expression of the pro-opiomelanocortin (POMC) precursor of alphaMSH. Insulin also inhibits arcuate nucleus expression of neuropeptide Y but its effects on other hypothalamic signaling systems are not known. Leptin-responsive neurons in the arcuate nucleus are hypothesized to project to the paraventricular nucleus and lateral hypothalamic area where they are proposed to influence the expression of peptides that regulate food intake. Future development of this model will incorporate brain pathways for integration of leptin and insulin adiposity signaling to the hypothalamus with meal-related signals that act in the caudal brainstem. Recent research showing that leptin and insulin enhance the satiety action of peripheral CCK, thereby causing meals to be terminated earlier and reducing cumulative food intake, suggests that hypothalamic pathways that are sensitive to leptin and insulin adiposity signals have anatomical connections with caudal brainstem neurons that respond to meal-related signals and regulate meal size. The recent findings that insulin alters the expression and function of neural transporters for dopamine and norepinephrine indicate that adiposity signals may influence food intake by acting on non-peptide neurotransmitter systems.