Circulating Amino Acid Concentrations Research Articles

Role of endogenously released cholecystokinin in determining postprandial insulin levels in man: effects of loxiglumide, a specific cholecystokinin receptor antagonist.

To estimate the contribution of postprandial cholecystokinin (CCK) responses to circulating insulin concentrations and insulin secretion, a specific CCK receptor antagonist (loxiglumide; 10 mg/kg body weight/h) or saline were infused intravenously in normal volunteers, beginning 90 min before insulin secretion was stimulated on separate occasions by the intraduodenal administrations of glucose, glucose and protein, and glucose plus protein with the admixture of pancreatin. The release of CCK (radioimmunoassay) was stimulated by the protein component of the nutrients from basal 2.4 +/- 0.4 to 8.0 +/- 1.2 pmol/l. CCK plasma levels were significantly higher with loxiglumide (p < 0.05). Glucose-dependent insulinotropic polypeptide (GIP) was also released by all nutrient mixtures. Loxiglumide significantly inhibited the amount of bilirubin and pancreatic enzymes recovered from duodenal aspirates. In contrast, in none of the experiments, C-peptide increments and hence insulin secretion rates were altered by loxiglumide. With glucose and protein as intraduodenal stimulus (no pancreatin added), the plasma amino acids rose significantly less (by approximately 50% of the control experiment) and the increment in insulin (but not C-peptide) concentrations was significantly reduced by loxiglumide. This is most likely explained by a change in insulin metabolic clearance. This effect cannot be a primary action of CCK because there was no similar effect of loxiglumide with the same intraduodenal stimulus plus added pancreatin. Pancreatic enzymes reduced maldigestion secondary to loxiglumide effects on pancreatic exocrine secretion: The increment in circulating amino acid concentrations was similar with and without loxiglumide. In conclusion, CCK does not alter insulin secretion and, therefore, is not an incretin hormone in man. Blocking CCK actions on the exocrine pancreas by loxiglumide, however, can secondarily cause reductions in postprandial insulin profiles by altering insulin clearance. These changes are possibly related to reductions in circulating amino acid concentrations.

Effect of starvation and protein-feeding on blood amino acid compartmentation of domestic fowl hatchlings

1. 1. The amino acid concentrations in plasma and blood cells of 5-day old domestic fowl hatchlings that received either standard feeding, protein-feeding or were starved have been determined. 2. 2. The effects of 5-day starvation or protein feeding did not alter significantly the combined amino acid concentration of blood plasma, but decreased blood cell levels. 3. 3. The patterns of individual amino acid changes observed in starvation or protein-feeding were similar in both groups when compared with those of controls. However, starvation-induced effects were actually more marked than those observed in protein-fed animals. 4. 4. The patterns of change with starvation of individual amino acids in the hatchling blood compartments were very different from those observed in mammals subjected to short or medium-term starvation. 5. 5. The mechanisms controlling circulating amino acid concentrations act in both situations studied to maintain the plasma amino acid concentrations despite marked changes in the availability of 2-amino nitrogen energy to the animal; changes in blood amino acid compartmentation buffering plasma amino acid availability.