Radioimmunoassay of cholecystokinin in plasma

A sensitive and specific radioimmunoassay for cholecystokinin (CCK) has been developed. Synthetic unsulfated carboxy-terminal fragment, CCK-8, was radioiodinated by the conventional Chloramine-T method. Antibodies were raised against sulfated CCK-8 covalently coupled to bovine thyroglobulin via 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. By purification, highly immunoreactive 125I-labeled CCK-8 was obtained. The antiserum was highly avid, and plasma could be assayed directly. The detection limit of the assay was 5 pmol of sulfated CCK-8 per liter. The assay measured fragments CCK-8, CCK-33, and CCK-39 with equimolar potency. CCK-4, gastrin, and vasoactive intestinal polypeptide were not detected, even at higher concentrations. The concentration of CCK, as the sum of these CCK peptides, in plasma during fasting was low (10.5 +/- 2.1 pmol/L, mean +/- SEM) but still detectable in all normal subjects examined (range, 6.4-20.1 pmol/L). After ingestion of a test meal, CCK in plasma increased rapidly, peaking at 41.3 (SEM 5.7) pmol/L at 40 min and remaining high for 3 h after the meal. This supports the concept that CCK has important roles in digestion and absorption.     

Cholecystokinin bioactivity in human plasma. Molecular forms, responses to feeding, and relationship to gallbladder contraction.

A sensitive and specific bioassay for the measurement of cholecystokinin (CCK) in human plasma was developed to determine the molecular forms of CCK in circulation, CCK responses to feeding, and the physiologic role of CCK in gallbladder contraction. First, plasma was quantitatively extracted and concentrated with octadecylsilylsilica, and the extracts were then assayed for their ability to stimulate amylase release from isolated rat pancreatic acini. Acini were highly sensitive to CCK whereas gastrin reacted only weakly in this system. With the assay, plasma levels of cholecystokinin octapeptide (CCK-8) bioactivity as low as 0.2 pM were detectable. CCK bioactivity in plasma was inhibited by the CCK antagonist, bibutyryl cyclic guanosine monophosphate, and was eliminated by immunoadsorption with an antibody directed against the carboxyl terminus of CCK. Detection of fasting levels of CCK was possible in all individuals tested and averaged 1.0 +/- 0.2 pM (mean +/- SE, n = 22) CCK-8 equivalents. Plasma CCK biological activity was normal in patients with gastrin-secreting tumors. After being fed a mixed liquid meal, CCK levels rose within 15 min to 6.0 +/- 1.6 pM. The individual food components fat, protein, and amino acids were all potent stimulants of CCK secretion; in contrast, glucose caused a significant but smaller elevation in plasma CCK levels. Gel filtration studies identified three major forms of CCK bioactivity in human plasma: an abundant form that eluted with CCK-33, a smaller form that eluted with CCK-8, and an intermediate form that eluted between CCK-33 and CCK-8. Ultrasonic measurements of gallbladder volume indicated that this organ decreased 51% in size 30 min after feeding a mixed liquid meal. This contraction occurred coincidentally with the increase in plasma CCK levels. Next CCK-8 was infused to obtain CCK levels similar to postprandial levels. This infusion caused a decrease in gallbladder volume, similar to that seen with a meal. The present studies indicate, therefore, that CCK can be bioassayed in fasting and postprandial human plasma. These studies also suggest that CCK may be an important regulator of gallbladder contraction.     

Physiological role for cholecystokinin in reducing postprandial hyperglycemia in humans.

It is known that the ingestion of glucose alone causes a greater increase in plasma glucose levels than ingestion of the same amount of glucose given with other nutrients. Since physiological plasma concentrations of cholecystokinin (CCK) prolong gastric emptying, it is proposed that after a meal, CCK may modify plasma glucose levels by delaying glucose delivery to the duodenum. To evaluate the effect of CCK on oral glucose tolerance, plasma CCK, insulin, and glucose levels and gastric emptying rates were measured in eight normal males before and after the ingestion of 60 g glucose with the simultaneous infusion of either saline or one of two doses of CCK-8 (12 or 24 pmol/kg per h). Gastric emptying rates were measured by gamma camera scintigraphy of technetium 99m sulfur colloid and plasma CCK levels were measured by a sensitive and specific bioassay. Basal CCK levels averaged 1.0 +/- 0.1 pM (mean +/- SEM, n = 8) and increased to 7.1 +/- 1.1 pM after a mixed liquid meal. After glucose ingestion, but without CCK infusion, CCK levels did not change from basal, and the gastric emptying t1/2 was 68 +/- 3 min. Plasma glucose levels increased from basal levels of 91 +/- 3.9 mg/dl to peak levels of 162 +/- 11 mg/dl and insulin levels increased from 10.7 +/- 1.8 microU/ml to peak levels of 58 +/- 11 microU/ml. After glucose ingestion, with CCK infused at 24 pmol/kg per h, plasma CCK levels increased to 8 pM and the gastric emptying t1/2 increased to 148 +/- 16 min. In concert with this delay in gastric emptying, peak glucose levels rose to only 129 +/- 17 mg% and peak insulin levels rose to only 24.2 +/- 4.2 microU/ml. With CCK at 12 pmol/kg per h, similar but less dramatic changes were seen. To demonstrate that endogenous CCK could modify the plasma glucose and insulin responses to oral glucose, oral glucose was given with 50 g of lipid containing long-chain triglycerides. This lipid increased peak CCK levels to 3.7 +/- 0.9 pM. Concomitant with this rise in CCK was a delay in gastric emptying and a lowering of plasma glucose and insulin values. To confirm that CCK reduced hyperglycemia by its effect on gastric motility, 36 g glucose was perfused directly into the duodenum through a nasal-duodenal feeding tube in four subjects. With duodenal perfusion of glucose, there was no change in plasma CCK levels, but plasma glucose levels increased from basal levels of 93+/-5 to 148+/-6 mg/dl and insulin levels rose from 10.6+/-3.5 to 29.5+/-5.2 microU/ml. When CCK was infused at 24 pmol/kg per h, neither the plasma glucose nor insulin responses to the duodenal administration of glucose were modified. Thus we conclude that CCK, in physiological concentrations, delays gastric emptying, slows the delivery of glucose to the duodenum, and reduces postprandial hyperglycemia. These data indicate, therefore, that CCK has a significant role in regulating glucose homeostasis in human.     

Measurement and characterisation of human cholecystokinin-like immunoreactivity (CCK-LI) in tissues by radioimmunoassay

Two radioimmunoassays specific for cholecystokinin-like immunoreactivity (CCK-LI) in human tissue are described. The first assay employed an antiserum (Z-69) directed to the sulphated tyrosine at the C-terminal end of CCK-33 and measured all biologically active molecular forms of CCK except the controversial C-terminal tetrapeptide amide (CCK4). The sensitivity of this assay was 0.6 pmol/g. A second assay (employing antiserum Z-91) measured CCK-LI forms larger than the octapeptide and had a sensitivity of 0.2 pmol/g. Both assays were characterised with endogenous human peptides. Acid (pH 2.5) and neutral extracts (pH 6.5) of human intestine and brain were assessed for CCK-LI concentrations and gel chromatography performed in the presence of 6 mol/l urea to elucidate the various molecular forms. Human cerebral cortex CCK-LI was almost all sulphated CCK-8, but large molecular mass forms were present, particularly in acid extracts, forming about 10% of the whole. Human duodenum and jejunum contained approximately equal amounts of large CCK, CCK 33/39 and of CCK-8. Both intestine and brain possess not yet isolated sulphated molecular forms which eluted between the pure CCK-8 and CCK-33/39 standards. The results obtained from this study indicate that the biosynthesis of CCK in human brain and gut is quantitatively different.     

The molecular nature of cholecystokinin in human plasma

Using a radioimmunoassay specific for the bioactive, tyrosine-sulfated sequence of cholecystokinin (CCK) we have studied the molecular nature of CCK in plasma from normal human subjects. CCK was extracted from postprandial plasma by Sep-Pak cartridges prior to Sephadex G-50 gel chromatography. Four CCK components eluting like CCK-58, CCK-33, CCK-22, and CCK-8, were identified in all samples. Of these, CCK-33- and CCK-8-like peptides predominated. The heterogeneity of circulating CCK emphasizes the importance of plasma assays that measure all bioactive forms of CCK.     

Metabolic clearance rate of arginine vasopressin in severe chronic renal failure.

1. The metabolic clearance rate of arginine vasopressin was determined using a constant infusion technique in normal subjects and patients with chronic renal failure immediately before commencing dialysis. Endogenous arginine vasopressin was suppressed in all subjects before the infusion with a water load. 2. Plasma arginine vasopressin concentrations were determined using a sensitive and specific radioimmunoassay after Florisil extraction. The detection limit of the assay was 0.3 pmol/l, and intra- and inter-assay coefficients of variation at 2 pmol/l were 9.7% and 15.3%, respectively. 3. In normal subjects, the metabolic clearance rate was determined at two infusion rates producing steady-state concentrations of arginine vasopressin of 1.3 and 4.4 pmol/l. In the patients with renal failure, a single infusion rate was used, producing a steady-state concentration of 1.5 pmol/l. 4. At comparable plasma arginine vasopressin concentrations, metabolic clearance rate was significantly reduced in patients with renal failure (normal 1168 +/- 235 ml/min versus renal failure 584 +/- 169 ml/min; means +/- SD; P < 0.001). 5. Free water clearance was significantly reduced in normal subjects during the arginine vasopressin infusion from 8.19 +/- 2.61 to -1.41 +/- 0.51 ml/min (P < 0.001), but was unchanged in the patients with renal failure after attaining comparable plasma arginine vasopressin concentrations. 6. In normal subjects there was a small but significant fall in metabolic clearance rate at the higher steady-state arginine vasopressin concentration (1168 +/- 235 ml/min at 1.3 pmol/l versus 1059 +/- 269 ml/min at 4.4 pmol/l; P = 0.016).(ABSTRACT TRUNCATED AT 250 WORDS)     

Vagal afferent pathway mediates physiological action of cholecystokinin on pancreatic enzyme secretion.

To establish the mechanism(s) and site(s) of action of cholecystokinin (CCK) on pancreatic secretion under physiological conditions, we used an in vivo model using anesthetized rats with pancreaticobiliary cannulas. Infusion of CCK-8 (10-160 pmol/kg per h) produced a dose-dependent increase in plasma CCK levels. CCK-8 infusion at 40 pmol/kg per h produced a plasma CCK level of 7.9 +/- 1.5 pM and an 80% increase in pancreatic protein output over basal. This level was closely approximated by a postprandial peak plasma CCK level by 6.2 +/- 1.1 pM. Pretreatment with atropine or hexamethonium completely abolished pancreatic protein response to low doses of CCK-8 (10-40 pmol/kg per h) but had only partial effect on doses > 40 pmol/kg per h. Bilateral vagotomy also abolished the pancreatic responses to low doses of CCK-8. Similarly perivagal treatment with a sensory neurotoxin, capsaicin, caused a complete inhibition of pancreatic protein secretion in response to CCK-8 infusion. In contrast, pancreatic protein responses to bethanechol were similar in control and capsaicin-treated rats. In separate studies we demonstrated that gastroduodenal but not jejunal application of capsaicin for 30 min abolished pancreatic protein secretion in response to physiological doses of CCK-8. In conclusion, CCK at physiological levels stimulates pancreatic enzyme secretion via a capsaicin-sensitive afferent vagal pathway originating from the gastroduodenal mucosa.     

Evaluation of beta-cell secretory capacity using glucagon-like peptide 1

OBJECTIVE: Beta-cell secretory capacity is often evaluated with a glucagon test or a meal test. However, glucagon-like peptide 1 (GLP-1) is the most insulinotropic hormone known, and the effect is preserved in type 2 diabetic patients. RESEARCH DESIGN AND METHODS: We first compared the effects of intravenous bolus injections of 2.5, 5, 15, and 25 nmol GLP-1 with glucagon (1 mg intravenous) and a standard meal (566 kcal) in 6 type 2 diabetic patients and 6 matched control subjects. Next, we studied another 6 patients and 6 control subjects and, in addition to the above procedure, performed a combined glucose plus GLP-1 stimulation, where plasma glucose was increased to 15 mmol/l before injection of 2.5 nmol GLP-1. Finally, we compared the insulin response to glucose plus GLP-1 stimulation with that observed during a hyperglycemic arginine clamp (30 mmol/l) in 8 patients and 8 control subjects. RESULTS: Peak insulin and C-peptide concentrations were similar after the meal, after 2.5 nmol GLP-1, and after glucagon. Side effects were less with GLP-1 than with glucagon. Peak insulin and C-peptide concentrations were as follows (C-peptide concentrations are given in parentheses): for patients (n = 12): meal, 277 +/- 42 pmol/l (2,181 +/- 261 pmol/l); GLP-1 (2.5 nmol), 390 +/- 74 pmol/l (2,144 +/- 254 pmol/l); glucagon, 329 +/- 50 pmol/l (1,780 +/- 160 pmol/l); glucose plus GLP-1, 465 +/- 87 pmol/l (2,384 +/- 299 pmol/l); for control subjects (n = 12): meal, 543 +/- 89 pmol/l (2,873 +/- 210 pmol/l); GLP-1, 356 +/- 51 pmol/l (2,001 +/- 130 pmol/l); glucagon, 420 +/- 61 pmol/l (1,995 +/- 99 pmol/l); glucose plus GLP-1, 1,412 +/- 187 pmol/l (4,391 +/- 416 pmol/l). Peak insulin and C-peptide concentrations during the hyperglycemic arginine clamp and during glucose plus GLP-1 injection were as follows: for patients: 475 +/- 141 pmol/l (2,295 +/- 379 pmol/l) and 816 +/- 268 pmol/l (3,043 +/- 508 pmol/l), respectively; for control subjects: 1,403 +/- 308 pmol/l (4,053 +/- 533 pmol/l) and 2,384 +/- 452 pmol/l (6,047 +/- 652 pmol/l), respectively. CONCLUSIONS: GLP-1 (2.5 nmol = 9 microg) elicits similar secretory responses to 1 mg glucagon (but has fewer side effects) and a standard meal. Additional elevation of plasma glucose to 15 mmol/l did not enhance the response further. The incremental response was similar to that elicited by arginine, but hyperglycemia had an additional effect on the response to arginine.     

Regulation of gastric emptying in humans by cholecystokinin.

In the present study we used a bioassay system for measuring plasma cholecystokinin (CCK) to evaluate whether CCK has a physiologic role in regulating gastric emptying in humans. Plasma CCK levels and gastric emptying after ingestion of a mixed liquid meal were determined in five normal male volunteers. Fasting CCK levels averaged 0.8 +/- 0.1 pM and increased to 6.5 +/- 1.0 pM within 10 min of drinking the mixed meal. CCK levels remained elevated for up to 90 min. Gastric emptying after a meal was slow; at the end of the 90 min 68% of the original volume remained in the stomach. The rate of gastric emptying of water was then measured in the same individuals with a simultaneous infusion of either saline, or one of two doses of CCK (12 pmol/kg per h and 24 pmol/kg per h). With the saline infusion, plasma CCK levels did not increase above basal and gastric contents emptied rapidly. At the end of 90 min only 7% of the original volume remained in the stomach. The lower dose of CCK resulted in a plasma level of 3.4 pM which both reproduced the average postprandial plasma level and caused a significant delay in gastric emptying. The higher dose of CCK achieved plasma levels of 8 pM and resulted in a delay in gastric emptying that was similar to that seen with the mixed meal. Since exogenous CCK at concentrations which occur postprandially delays gastric emptying, we conclude that CCK is a physiologic regulator of gastric emptying.     

Plasma concentrations and comparisons of brain natriuretic peptide and atrial natriuretic peptide in normal subjects, cardiac transplant recipients and patients with dialysis-independent or dialysis-dependent chronic renal failure.

1. We have developed a radioimmunoassay for the measurement of immunoreactive brain natriuretic peptide (1-32) in human plasma. Simultaneous measurements of atrial natriuretic peptide have also been carried out to allow for direct comparison between circulating brain natriuretic peptide and atrial natriuretic peptide. Plasma levels of immunoreactive brain natriuretic peptide (means +/- SEM) were 1.1 +/- 0.1 pmol/l in 36 normal healthy subjects and were significantly elevated in cardiac transplant recipients (18.8 +/- 3.9 pmol/l, n = 12) and in patients with dialysis-independent (8.8 +/- 1.5 pmol/l, n = 11) or dialysis-dependent (41.6 +/- 8.8 pmol/l, n = 14) chronic renal failure. Similarly, in these groups of patients plasma levels of atrial natriuretic peptide were also significantly raised when compared with those in the group of normal healthy subjects. 2. The plasma level of atrial natriuretic peptide was significantly higher than that of brain natriuretic peptide in normal subjects and in patients with dialysis-independent chronic renal failure, with ratios (atrial natriuretic peptide/brain natriuretic peptide) of 2.8 +/- 0.2 and 2.2 +/- 0.3, respectively. However, in both cardiac transplant recipients and patients on dialysis plasma levels of atrial natriuretic peptide and brain natriuretic peptide were similar, with ratios of 1.3 +/- 0.2 and 1.0 +/- 0.1, respectively, in these two groups. 3. Plasma levels of brain natriuretic peptide and atrial natriuretic peptide were significantly correlated in the healthy subjects and within each group of patients. When all groups were taken together, there was an overall correlation of 0.90 (P < 0.001, n = 73).(ABSTRACT TRUNCATED AT 250 WORDS)     

Human pancreatic and biliary responses to physiological concentrations of cholecystokinin octapeptide

To determine the functional significance of physiological plasma concentrations of cholecystokinin, five volunteers each received graded doses of intravenous infusions of cholecystokinin octapeptide (CCK-8). At each dose plasma concentrations of CCK-8 were determined and pancreatic and biliary outputs were measured. Threshold plasma concentrations of CCK-8 for augmenting pancreatic trypsin secretion were undetectable (less than 3 pmol/l), and maximal trypsin output of 21.9 +/- 1.95 k-i.u./30 min was produced by 17.1 +/- 6.4 pmol of CCK-8/1. Calculated halfmaximal output was produced by 4.7 pmol of CCK-8/1. Maximal trypsin output during infusions of CCK-8 was significantly less than that after a combination of the CCK-like peptide, caerulein, and secretin (32.95 +/- 2.16 k-i.u./30 min, P less than 0.001). Biliary bile acid and bilirubin outputs were significantly augmented only when plasma concentrations of CCK-8 were greater than 5 pmol/l. Plasma concentrations of CCK-8 in the low picomolar range exert significant effects on pancreatic and biliary secretion. CCK-8 fulfills the criteria for a circulating hormone.     

Increased plasma cholecystokinin levels and small gall bladders in adult patients with cystic fibrosis.

1. In patients with cystic fibrosis, abnormalities in plasma cholecystokinin level and gall-bladder emptying may contribute to the development of maldigestion and gall-stones. 2. Therefore, we have measured plasma cholecystokinin levels and gall-bladder volumes before and after ingestion of a standard breakfast in eight adult patients with cystic fibrosis and in eight normal control subjects. 3. In the patients with cystic fibrosis basal (2.8 +/- 0.4 pmol/l; P less than 0.05, t-test) and maximum post-prandial (5.7 +/- 0.5 pmol/l; P less than 0.05, t-test) plasma cholecystokinin levels were significantly higher than those in the control subjects (1.9 +/- 0.1 pmol/l, and 4.5 +/- 0.2 pmol/l, respectively). On the other hand, integrated plasma cholecystokinin secretion in response to the meal was similar (t-test, P = 0.4 versus control subjects). The increased plasma cholecystokinin levels in the patients with cystic fibrosis were accompanied by reduced gallbladder volumes in both the basal (7.8 +/- 2.1 cm3 versus 20.9 +/- 2.3 cm3 in control subjects; P less than 0.005, t-test) and the post-prandial state (2.2 +/- 1.0 cm3 versus 4.8 +/- 0.8 cm3 in control subjects; P = 0.06, t-test). Gall-bladder emptying in the patients with cystic fibrosis was well preserved (70 +/- 7% versus 78 +/- 9% in control subjects; P = 0.4, t-test). 4. In comparison with normal control subjects, patients with cystic fibrosis have an increased basal plasma cholecystokinin level and a reduced gall-bladder volume, whereas post-prandial gall-bladder emptying and plasma cholecystokinin secretion are not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pressor effect of arginine vasopressin in progressive autonomic failure

The blood pressure (BP) and heart rate (HR) responses to 5 min incremental intravenous infusions of noradrenaline (NA) and arginine vasopressin (AVP) were investigated both in patients with progressive autonomic failure (PAF) and in normal volunteers. Stepwise infusion of NA at rates of 300-3000 pmol min-1 kg-1 produced a bradycardia and a dose related increase in BP in normal subjects. In subjects with PAF there was no significant HR response but the dose-BP response was shifted to the left with significant pressor responses at infusion rates of 60-300 pmol min-1 kg-1. Stepwise infusion of AVP at 0.2-5.0 pmol min-1 kg-1 caused transient bradycardia but no pressor response in seven normal volunteers. Further increases in AVP infusion in three other subjects achieved plasma AVP levels as high as 3000-4000 pmol/l, and still no significant pressor response was observed. Stepwise infusion of AVP at 0.05-2.0 pmol min-1 kg-1 in the eight subjects with PAF resulted in a pressor response without any change in HR. During this infusion plasma AVP increased from 0.8 +/- 0.2 (mean +/- SEM) to 30 +/- 2 pmol/l. A significant pressor response was already apparent at a plasma AVP level of 5.5 +/- 1.8 pmol/l.     

Effects of a novel cholecystokinin (CCK) receptor antagonist, MK-329, on gallbladder contraction and gastric emptying in humans. Implications for the physiology of CCK.

To explore the physiology of cholecystokinin (CCK) in humans, we investigated the effect on gallbladder contraction and gastric emptying of a recently developed CCK receptor antagonist, MK-329. In a double-blind, four-period crossover study eight subjects received single doses of 0.5, 2, or 10 mg MK-329, or placebo, followed by an intravenous infusion of CCK-8 (30 pmol/kg.h). In placebo-treated subjects gallbladder volumes decreased on average to 43% of initial volumes after 2 h of CCK infusion. MK-329 caused a dose-dependent inhibition of CCK-stimulated gallbladder contraction with 10 mg producing complete blockade (P less than 0.01, cf. placebo). Gallbladder contraction and gastric emptying rates after a mixed meal were then measured in a two-period crossover study. Subjects received placebo or 10 mg of MK-329 2 h before eating. Gastric emptying of both solids and liquids was measured simultaneously by gamma scintigraphy. In placebo-treated subjects plasma CCK levels increased postprandially to 2.3 pM, gallbladder volumes decreased 68.4 +/- 3.8% (SE), and the times for 50% emptying of liquids and solids from the stomach were 58 +/- 10 and 128 +/- 8 min, respectively. In MK-329-treated subjects there was a marked elevation in peak CCK levels to 13.8 pM (P less than 0.01, cf. placebo), and gallbladder contraction was completely inhibited. Solid and liquid emptying rates were unaffected. These findings demonstrate that (a) MK-329 is a potent, orally active antagonist of CCK in humans, and (b) CCK is the major regulator of postprandial gallbladder contraction. These data also support the concept of negative feedback regulation of CCK secretion and suggest that mechanisms other than CCK play a dominant role in the regulation of postprandial gastric emptying rates.     

Identification and measurement of molecular variants of cholecystokinin in duodenal mucosa and plasma. Diminished concentrations in patients with celiac disease.

The amount and type of cholecystokinin (CCK) in duodenal extracts and plasma of celiac patients and normal subjects was studied by radioimmunoassay and gel filtration. In both groups there were similar patterns of molecular forms in extracts of duodenal biopsies, but concentrations in celiac disease were significantly depressed. In boiling water extracts of duodenal mucosa from both groups a factor with the properties of the COOH-terminal octapeptide of cholecystokinin predominated, but there were also significant amounts of a larger molecular weight form. In acid extracts of mucosa a factor with the properties of the 33 or 39 residue form was identified in amounts that were approximately 25% those of CCK8; there were also similar amounts of an acid-soluble form that had an apparent molecular weight higher than CCK39. Plasma immunoreactive cholecystokinin was studied after concentration by immunoaffinity adsorption and fractionation by gel filtration. In normal subjects fasting CCK-like immunoreactivity was less than 0.8 pmol/liter, and after a light breakfast increased to 2.0 +/- 0.7 (range 1.0 to 4.8) pmol/liter; CCK8-like activity accounted for all the increased immunoreactivity. In five of six celiac patients the concentrations of both fasting and postprandial CCK-like immunoreactivity in plasma were undetectable (less than 0.8 pmol/liter). We conclude that diminished production and release of CCK could account for the impaired pancreatic and gall bladder responses to intraluminal stimuli in celiac disease.     

Effect of acarbose on insulin sensitivity in elderly patients with diabetes

OBJECTIVE: To study the effect of acarbose, an alpha-glucosidase inhibitor, on insulin release and insulin sensitivity in elderly patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: Elderly patients with type 2 diabetes were randomly treated in a double-blind fashion with placebo (n = 23) or acarbose (n = 22) for 12 months. Before and after randomization, subjects underwent a meal tolerance test and a hyperglycemic glucose clamp study designed to measure insulin release and sensitivity. RESULTS: After 12 months of therapy there was a significant difference in the change in fasting plasma glucose levels (0.2 +/- 0.3 vs. -0.5 +/- 0.2 mmol/l, placebo vs. acarbose group, respectively; P < 0.05) and in incremental postprandial glucose values (-0.4 +/- 0.6 vs. -3.5 +/- 0.6 mmol/l, placebo vs. acarbose group, P < 0.001) between groups. There was a significant difference in the change in HbA(1c) values in response to treatment (0.4 +/- 0.2 vs. -0.4 +/- 0.1%, placebo vs. acarbose group, P < 0.01). The change in fasting insulin in response to treatment (-2 +/- 2 vs. -13 +/- 4 pmol/l, placebo vs. acarbose group, P < 0.05) and incremental postprandial insulin responses (-89 +/- 26 vs. -271 +/- 59 pmol/l, placebo vs. acarbose group, P < 0.01) was also significantly different between groups. During the hyperglycemic clamps, glucose and insulin values were similar in both groups before and after therapy However, there was a significant difference in the change in insulin sensitivity in response to treatment between the placebo and the acarbose groups (0.001 +/- 0.001 vs. 0.004 +/- 0.001 mg/kg x min(-1) [pmol/l](-1), respectively, P < 0.05) CONCLUSIONS: Acarbose increases insulin sensitivity but not insulin release in elderly patients with diabetes.     

Radio-immunoassays for glucagon-like peptides 1 and 2 (GLP-1 and GLP-2)

Gene-sequencing studies have shown that the glucagon precursor contains two additional glucagon-like sequences, the so-called glucagon-like peptides 1 and 2 (GLP-1 and GLP-2). We developed radio-immunoassays against synthetic peptides corresponding to these sequences. Antisera were raised in rabbits after carbodiimide conjugation of peptides to BSA. The selected antisera showed neither mutual cross-reactivity nor cross-reacted with any other peptide of the glucagon family. Trypsin digestion experiments showed that both antisera were directed against the C-terminus of the antigen peptides. Labelling was performed with chloramine T, and separation with plasma-coated charcoal. The detection limit was 7 and 25 pmol/l for GLP-1 and GLP-2. Accurate measurement of both peptides in plasma required extraction. Optimum recovery was obtained with ethanol at 75% (final concentration). The concentrations measured in fasting plasma from 10 normal subjects were 107 +/- 7 pmol/l and 151 +/- 14 pmol/l for GLP-1 and GLP-2, respectively. After a mixed meal the concentrations rose slowly for 2 h reaching 145 +/- 13 and 225 +/- 15 pmol/l.     

Effect of angiotensin-converting enzyme inhibition on plasma brain natriuretic peptide levels in patients with heart failure.

1. The aim of this study was to examine the effect of captopril, an angiotensin-converting enzyme inhibitor, on plasma levels of human brain natriuretic peptide-like immunoreactivity (hBNP-li) in patients with congestive heart failure. 2. Six male patients (aged 52-74 years) with mild to moderate congestive heart failure were studied on two occasions in the semi-recumbent position. After a 30 min rest, patients were randomized to receive oral tablets of either captopril (6.25 mg followed by 25 mg 2 h later) or placebo in a single-blind manner. Plasma hBNP-li, atrial natriuretic peptide-like immunoreactivity (ANP-li) and angiotensin II-like immunoreactivity (ANG II-li) levels and blood pressure were measured. 3. Baseline plasma hBNP-li and ANP-li levels in these patients with mild to moderate congestive heart failure were 13.5 +/- 3.2 pmol/l and 50.9 +/- 11.8 pmol/l, respectively. In 11 healthy male subjects aged 20-23 years, the peripheral plasma hBNP-li and ANP-li levels were 1.3 +/- 0.2 pmol/l and 5.6 +/- 1.7 pmol/l, respectively. In all patients, captopril decreased the plasma ANG II-li level (from 24.3 +/- 8.1 to 6.6 +/- 3.2 pmol/l, P < 0.05) and mean arterial blood pressure (from 92 +/- 3 to 80 +/- 3 mmHg, P < 0.05). Compared with placebo, captopril treatment was associated with significant reductions in plasma hBNP-li (from 14.3 +/- 3.0 to 12.8 +/- 2.1 pmol/l, P < 0.05) and in plasma ANP-li (from 53.9 +/- 1.11 to 36.8 +/- 7.6 pmol/l, P < 0.05) levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Circulating levels of calcitonin gene-related peptide in patients with medullary thyroid carcinoma

Calcitonin gene-related peptide, originally found in rat medullary thyroid carcinoma cells, was measured by radioimmunoassay in plasma samples with added aprotinin from 17 normal volunteers and 21 patients with medullary thyroid carcinoma. The concentrations were below 75 pmol/l in all 17 normal subjects with a mean of 33 +/- 19 pmol/l plasma. In the patients, the plasma calcitonin gene-related peptide concentrations ranged from below 5 pmol/l to 236 pmol/l, although the mean (36 +/- 48 pmol/l) was not significantly different from the mean normal level. Increase in the plasma calcitonin gene-related peptide level was observed in 2 of 5 patients in response to infusion of 4.3 mg/kg of calcium for 10 minutes and in 3 of 5 patients in response to infusion of 4 micrograms/kg of tetragastrin for 5 minutes. These observations suggest that measurement of calcitonin gene-related peptide level may be helpful in determination of diseases in which the level of calcitonin is of less diagnostic value.     

A radioimmunoassay for neurotensin in human plasma

A specific radioimmunoassay for neurotensin in plasma has been developed with a sensitivity of 2 pmol/l of plasma. The antiserum was directed towards the amino terminal region of neurotensin and did not cross-react with other gastrointestinal peptides. Non-specific interference was eliminated and the sensitivity increased by extracting the plasma samples with ethanol prior to assay. Within- and between-assay coefficients of variation were 7.8% and 12% respectively. The mean plasma concentration of neurotensin in 30 fasting subjects was 29 ± 4 pmol/l. A mixed meal increased plasma neurotensin from 16 ± 2 to 53 ± 6 pmol/l at 2 h.