Secretin, cholecystokinin and newer gastrointestinal hormones (second of two parts)

Correlation between release of cholecystokinin and contraction of the gallbladder in patients with gallstones

The role of endogenously released cholecystokinin (CCK) in mediating gallblader (GB) contraction was evaluated in 12 normal volunteers and 24 patients with gallstones (11 additional gallstone patients were excluded because of failure of adequate ultrasonographic visualization). CCK concentrations before and after oral administration of fat (Lipomul((R))) were measured by a specific radioimmunoassay. CCK release was correlated with changes in GB volume determined simultaneously by ultrasonography. On the basis of gallbladder contraction and operative findings, gallstone patients were divided into "contractors" (14), "noncontractors" (6), and "hydrops" (4). Lipomul caused prompt release of CCK in normal volunteers and all groups of gallstone patients. The changes (basal to peak) in plasma CCK (pg/ml) for the different groups were as follows: normal volunteers (108 +/- 9 to 200 +/- 16), contractors (77 +/- 10 to 128 +/- 13), noncontractors (59 +/- 7 to 159 +/- 38), and hydrops (43 +/- 5 to 113 +/- 47). The total integrated output of CCK (0-60 min) was greater in normal volunteers (3975 +/- 762 pg-min/ml) than in contractors (1530 +/- 567 pg-min/ml). Lipomul caused similar GB contraction in normal volunteers and contractors (from basal volumes to maximal contraction); these changes were from 19.5 +/- 2.3 ml to 5.6 +/- 1.0 ml in normal volunteers, and from 19.6 +/- 3.2 to 5.2 +/- 1.0 in contractors. Plasma concentrations of CCK and GB volume were highly correlated in the 12 normal volunteers (r = -0.89, p < 0.01) and in the 14 contractors (r= -0.99, p < 0.01)), but the GB was significantly (p < 0.01) more sensitive to changes in plasma CCK in the gallstone contractors than in the normal volunteers. The authors suggest that there may be two groups of gallstone patients, noncontractors and contractors. Stasis may be important in the pathogenesis of gallstones in the noncontractors, whereas in contractors, the authors speculate that an abnormality in the CCK-gallbladder relationship (characterized by diminished CCK release and increased GB sensitivity to CCK) may be involved in the evolution of the disease.

Effects of caerulein and bombesin on insulin and glucagon secretion from the isolated, perfused rat pancreas

Caerulein nd bombesin, peptides first isolated from amphibian skin, act upon the mammalian gastrointestinal tract. To determine if these peptides influence mammalian endocrine pancreatic function, we tested their effects on the isolated, perfused rat pancreas. In these experiments, we examined effects of constant infusions of either caerulein (10(-11) M through 10(-8) M) or bombesin (10(11) M through 3.0 . 10(-7) M) which were superimposed upon glucose. Secretory studies consisted of a 20-min basal period (60 mg/dl glucose), then a 15-min infusion of glucose (150 mg/dl). Effects of the peptides (10(-9) M) upon the response to post-glucose arginine (168 mg/dl), confusion with glucose (60 mg/dl) for 15 min. were also studied. Neither peptide had any effect on basal insulin secretion. However, both peptides had distinct effects on insulin responses to the stimuli. Both caerulein and bombesin produced enhancement of glucose-induced insulin secretion, increasing total insulin secretion in a dose-dependent manner. Only caerulein enhanced arginine-induced insulin secretion. These peptides had no effect upon arginine-induced glucagon secretion.

Failure to induce reactive hypoglycaemia by drinking a starch-based alcohol beverage (sorghum beer)

Alcohol is a well-recognised cause of fasting hypoglycaemia but may also provoked reactive hypoglycaemia when drunk together with a carbohydratee mixer. In this study the ability of sorghum beer (an 'in-built' alcohol-starch beverage widely enjoyed in Southern Africa) to induce reactive hypoglycaemia was compared with "gin and tonic' in eight non-obese health African men. After an overnight fast, each subject drank, in random sequence on their different occasions, 2 litres of sorghum beer (carbohydrat content approximately 5% and alcohol concentration 2.24 g/dl-2.8% v/v), the same volume of a control solution providing a similar carbohydrate load, or a gin and standard tonic water mixture. No evidence of reactive hypoglycaemia was apparent during the 5 hours after the beginning of the sorghum beer tolerance tests, despite a mean peak blood alcohol level reaching 80 mg/dl. both the peak and total plasma insulin responses were significantly reduced (p less than or equal to 0.05) when compared to the brisk responses elicited by the carbohydrate solution alone and the gin and tonic drinks, with consequent hypoglycaemia. These data suggest that African home-brews are not potent causes of reactive hypoglycaemia, although they may be implicated in the development of ethanol-induced hypoglycaemia in the fasting state.

Fat malabsorption--advances in our understanding

The intestinal absorption of triglyceride constitutes a multistep process with active involvement of the pancreatobiliary system, the intestine and lymphatics. It is only through the integrated function of these organs that dietary triglyceride can be efficiently absorbed and delivered to the peripheral blood for subsequent metabolism. In this review we discuss each aspect of triglyceride absorption and chylomicron formation and illustrate how various diseases may interfere with the process resulting in fat malabsorption. In addition, the role of the intestine as a major synthetic source of lipoprotein constituents for circulating lipoproteins is discussed.

Effects of gastrointestinal hormones on transport by peritoneal dialysis

Because the gastrointestinal hormones are known to dilate the splanchnic vasculature, their effects on transport of water and solutes during peritoneal dialysis were studied in an experimental model, the rabbit. In unanesthetized rabbits, dialysate volume was calculated by isotope dilution, and clearances were estimated by dialysate/plasma concentration ratio factored by minute volume. With isotonic dialysis solution, the mean increment in dialysate volume per minute of intraperitoneal dwell was 0.19 ml/kg/min, and mean clearances of creatinine and urea were 0.71 and 0.90 ml/kg/min, respectively. When administered intravenously, secretin significantly augmented osmotically induced water flux, but not when given intraperitoneally. Neither glucagon nor cholecystokinin affected dialysate volume. Intravenously, but not intraperitoneally, glucagon increased peritoneal clearances of creatinine and urea to more than 150% of control values. Neither cholecystokinin nor secretin augmented significantly peritoneal mass transport when given by either route. The data suggest that the site of acton is the endothelial surface of the membrane, that the mechanisms of augmenting transport involve increased permeability and/or surface area, and that agents which combine an increase in mass transport and capillary filtration coefficient may be clinically useful.

Effects of cholecystokinin-pancreozymin on bile flow and biliary bile salt secretion in the cholecystectomized animal

The effects of an intravenous infusion of cholecystokinin-pancreozymin on bile secretion were studied in 13 unanesthetized and cholecystectomized piglets. The results demonstrate that CCK-PZ induces a significant increase of bile flow and bile salt excretion. The excretion patterns for bilirubin and Ioglycamide, however, showed a slight but not significant decrease. Peripheral hemodynamic parameters remained unchanged. A detailed analysis of these results suggests that CCK-PZ induces an increase of biliary bile salt secretion by stimulation of intestinal motility and enhancement of bile salt circulation within the enterohepatic circulation (EHC). In combination with previous studies on the effects of spasmolytics on biliary bile salt excretion these results therefore emphasize, that the intestinal motility and transit time might play a role in the physiology and pathophysiology of biliary bile salt secretion.

Acid and endocrine responses to meals varying in pH in normal and duodenal ulcer subjects

Recent studies suggest that duodenal ulcers may develop because of increased drive to secrete acid and decreased effectiveness of feedback mechanisms that inhibit acid output. This study was designed to compare gastric acid, gastrin, gastric inhibitory peptide (GIP) and secretin responses to meals (varying in pH) in 12 normal subjects and nine duodenal ulcer patients. Acid secretion was measured by an intragastric titration method which allows actual measurement of acid response to food within the stomach (ten per cent amino acid meal (AAM) adjusted to various pH levels, 7-1.5). Blood samples were collected at each pH level for radioimmunoassay of gastrin, secretin and GIP. Gastric acid and gastrin responses to AAM were found to be significantly greater in duodenal ulcer patients than in normal subjects. In duodenal ulcer patients, acid response to AAM at pH 7 or 5.5 reached 82% of Histalog maximum. Decreasing the pH of the meal resulted in a stepwise reduction in both acid secretion and gastrin in normal subjects and duodenal ulcer patients. At pH 1.5, acid inhibition was complete, but gastrin inhibition was partial. Secretin increased significantly at pH 1.5; there was no difference in secretin release between the groups. Plasma GIP was highest at pH 7 in all individuals. Use of a marker substance showed 80% recovery of AAM at pH 7-4; below pH 4, recovery rose to about 90%. We conclude that gastric acid and gastrin release are pH-dependent in normal and duodenal ulcer subjects. Inhibition of gastric secretion by acidified meals is associated with a pH-dependent suppession of gastrin and GIP levels and elevation of plasma secretin. This study confirms increased acid and gastrin responses in duodenal ulcer patients but shows no evidence of defective feedback inhibition of gastric secretion and gastrin release.