Correlation of regional cerebral blood flow and change of plasma sodium concentration during genesis and satiation of thirst.
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Positron emission tomography studies were conducted during genesis of moderate thirst by rapid i.v. infusion of hypertonic saline (0.51 M) and after satiation of thirst by drinking water. The correlation of regional cerebral blood flow with the change in the plasma Na concentration showed a significant group of cerebral activations in the anterior cingulate region and also a site in the middle temporal gyrus and in the periaqueductal gray. Strongest deactivations occurred in the parahippocampal and frontal gyri. The data are consistent with an important role of the anterior cingulate in the genesis of thirst. (+info)
Effect of the glycemic index and content of indigestible carbohydrates of cereal-based breakfast meals on glucose tolerance at lunch in healthy subjects.
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BACKGROUND: Diets with a low glycemic index (GI) have been shown to improve glucose tolerance in both healthy and diabetic subjects. Two potential mechanisms are discussed in relation to long-term metabolic effects: a decreased demand for insulin in the postprandial phase and formation of short-chain fatty acids from fermentation of indigestible carbohydrates in the colon. OBJECTIVE: The objective was to study the effect of the GI and the indigestible carbohydrate--resistant starch (RS) and dietary fiber (DF)--content of cereal-based breakfasts on glucose tolerance at a second meal (lunch) in healthy subjects. DESIGN: The effects of 7 test breakfasts with known GIs (GI: 52-99) and RS + DF contents (2-36 g) were evaluated. White-wheat bread was used as a reference breakfast (high GI, low RS + DF content). Glucose and insulin responses after the second meal were measured in healthy subjects. In addition, the satiating capacity of 4 of the 7 test breakfasts was estimated before and during the second meal. RESULTS: Two of the 4 low-GI breakfasts improved glucose tolerance at the second meal. Only these 2 breakfasts were capable of postponing the in-between-meal fasting state. There was no measurable effect of fermentable carbohydrates on glucose tolerance at the second meal. The highest satiety score was associated with the barley breakfast that had a low GI and a high RS + DF content. CONCLUSIONS: Glucose tolerance can improve in a single day. Slow absorption and digestion of starch from the breakfast meal, but not the content of indigestible carbohydrates in the breakfast meal, improved glucose tolerance at the second meal (lunch). (+info)
A rapid feedback signal is not always necessary for termination of a drinking bout.
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When a pig is deprived of drinking water, a deficit of body water develops that is corrected when the pig drinks to satiation. If food is available during the deprivation, the stimulus to drinking is plasma hyperosmolality. Because of the delay in correction of plasma hyperosmolality as ingested water is slowly absorbed, it has been thought that a rapid inhibitory signal from the digestive tract is necessary to prevent overdrinking. This concept was tested by measuring changes in plasma osmolality before and during drinking after such deprivation and also after infusion of hypertonic saline. As drinking began, there was a rapid fall of plasma osmolality to levels insufficient to drive drinking by the time drinking ended. This fall of plasma hyperosmolality to subthreshold levels while the pig is drinking seems to make a rapid inhibitory control signal from the digestive tract unnecessary to terminate the drinking bout under these conditions. (+info)
Neuroanatomical correlates of hunger and satiation in humans using positron emission tomography.
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The central role of the hypothalamus in the origination and/or processing of feeding-related stimuli may be modulated by the activity of other functional areas of the brain including the insular cortex (involved in enteroceptive monitoring) and the prefrontal cortex (involved in the inhibition of inappropriate response tendencies). Regional cerebral blood flow (rCBF), a marker of neuronal activity, was measured in 11 healthy, normal-weight men by using positron emission tomography in a state of hunger (after 36-h fast) and a state of satiation (after a liquid meal). Hunger was associated with significantly increased rCBF in the vicinity of the hypothalamus and insular cortex and in additional paralimbic and limbic areas (orbitofrontal cortex, anterior cingulate cortex, and parahippocampal and hippocampal formation), thalamus, caudate, precuneus, putamen, and cerebellum. Satiation was associated with increased rCBF in the vicinity of the ventromedial prefrontal cortex, dorsolateral prefrontal cortex, and inferior parietal lobule. Changes in plasma insulin concentrations in response to the meal were negatively correlated with changes in rCBF in the insular and orbitofrontal cortex. Changes in plasma free fatty acid concentrations in response to the meal were negatively correlated with changes in rCBF in the anterior cingulate and positively correlated with changes in rCBF in the dorsolateral prefrontal cortex. In conclusion, these findings raise the possibility that several regions of the brain participate in the regulation of hunger and satiation and that insulin and free fatty acids may be metabolic modulators of postprandial brain neuronal events. Although exploratory, the present study provides a foundation for investigating the human brain regions and cognitive operations that respond to nutritional stimuli. (+info)
Glucagon-like peptide-1 promotes satiety and reduces food intake in patients with diabetes mellitus type 2.
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Glucagon-like peptide-1-(7-36) amide (GLP-1) is an incretin hormone of the enteroinsular axis. Recent experimental evidence in animals and healthy subjects suggests that GLP-1 has a role in controlling appetite and energy intake in humans. We have therefore examined in a double-blind, placebo-controlled, crossover study in 12 patients with diabetes type 2 the effect of intravenously infused GLP-1 on appetite sensations and energy intake. On 2 days, either saline or GLP-1 (1.5 pmol. kg-1. min-1) was given throughout the experiment. Visual analog scales were used to assess appetite sensations; furthermore, food and fluid intake of a test meal were recorded, and blood was sampled for analysis of plasma glucose and hormone levels. GLP-1 infusion enhanced satiety and fullness compared with placebo (P = 0.028 for fullness and P = 0.026 for hunger feelings). Energy intake was reduced by 27% by GLP-1 (P = 0.034) compared with saline. The results demonstrate a marked effect of GLP-1 on appetite by showing enhanced satiety and reduced energy intake in patients with diabetes type 2. (+info)
Central leptin modulates behavioral and neural responsivity to CCK.
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The mechanisms through which leptin, the protein product of the ob gene, affects food intake remain to be determined. To assess whether the actions of leptin depend on modulation of within-meal satiety signals, we measured the effect of third ventricular leptin administration on the satiety actions of CCK. Leptin (10 micrograms) administered 1 h before 30-min access to a liquid diet had no effect on intake when administered alone, but doses of 3.5 or 10 micrograms dose dependently increased the suppression of intake produced by 1 nmol/kg CCK. Examination of patterns of c-Fos activation induced by 3.5 micrograms leptin and 1 nmol/kg CCK revealed that the combination produced significant c-Fos activation within the area postrema and the caudal and medial nucleus of the solitary tract (NST) compared with either leptin or CCK treatments alone. The leptin-CCK combination also resulted in increased c-Fos activation within the paraventricular nucleus of the hypothalamus above that produced by leptin alone. These data suggest that the actions of leptin in food intake are mediated through its ability to modulate responsivity to within-meal satiety signals. (+info)
Hyperglycemia attenuates the gastrokinetic effect of erythromycin and affects the perception of postprandial hunger in normal subjects.
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OBJECTIVE: The major aims of this study were to determine in normal subjects whether the effects of erythromycin on gastric emptying, postprandial hunger, and fullness are modified by the blood glucose concentration. RESEARCH DESIGN AND METHODS: A total of 10 normal subjects (aged 20-39 years) underwent concurrent measurements of gastric emptying, blood glucose, hunger, and fullness on four separate occasions: twice during euglycemia (approximately 4 mmol/l) and twice during hyperglycemia (approximately 15 mmol/l). Either erythromycin (3 mg/kg) or saline (0.9%) was administered intravenously immediately before ingestion of a radioisotopically labeled solid meal. RESULTS: Gastric emptying was slower (P < 0.0001) during hyperglycemia when compared with euglycemia after both erythromycin and saline administration. During hyperglycemia, erythromycin reduced the lag phase (77.8 +/- 12.6 vs. 20.3 +/- 7.3 min; P < 0.05) but had no effect on the postlag emptying rate (0.32 +/- 0.077% per min vs. 0.24% per min). Hunger decreased (P < 0.001) and fullness increased (P < 0.001) after the meal. Postprandial hunger was less during hyperglycemia after saline infusion (P < 0.05) but not after erythromycin. Hunger was greater after erythromycin during both hyperglycemia and euglycemia (P < 0.05). CONCLUSIONS: At a blood glucose concentration of approximately 15 mmol/l, 1) gastric emptying of a solid meal is slower, when compared with euglycemia, even after administration of erythromycin; 2) the effect of erythromycin on gastric emptying of a solid meal is attenuated; and 3) the perception of postprandial hunger is reduced. (+info)
The role of apolipoprotein A-IV in food intake regulation.
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Apolipoprotein (apo) A-IV is a glycoprotein synthesized by the human intestine. In rodents, both the small intestine and the liver secrete apo A-IV; the small intestine, however, is by far the major organ responsible for the circulating apo A-IV. Intestinal apo A-IV synthesis is markedly stimulated by fat absorption and appears not to be mediated by the uptake or reesterification of fatty acids to form triglycerides. Rather, it is the formation of chylomicrons that acts as a signal for the induction of intestinal apo A-IV synthesis. Intestinal apo A-IV synthesis is also enhanced by a factor from the ileum and that factor is probably peptide tyrosine-tyrosine (PYY). The inhibition of food intake by apo A-IV is probably mediated centrally. The stimulation of intestinal synthesis and secretion of apo A-IV by lipid absorption are rapid; thus, apo A-IV likely plays a role in the short-term regulation of food intake. Other evidence suggests that apo A-IV may also be involved in the long-term regulation of food intake and body weight. Chronic ingestion of a high fat diet blunts the intestinal apo A-IV response to lipid feeding and may explain why the chronic ingestion of a high fat diet predisposes both animals and humans to obesity. (+info)