Biodistribution and dosimetry of 99mTc-BTAP-annexin-V in humans

The purpose of this study was to determine the biodistribution and the associated radiation dose of technetium-99m 4,5-bis(thioacetamido)pentanoyl-annexin-V (99mTc-Apomate), a tracer proposed for the study of apoptosis. Eight patients (including two females) with normal kidney and liver functions were included in the study. An activity of 580 +/- 90 MBq of 99mTc-Apomate was injected intravenously, immediately followed by a dynamic study of 30 frames of 1 min each. At about 1 h, 4 h and 20 h p.i., whole-body scans were acquired. All activity distributions were measured using a dual-head gamma camera. Before injection of activity, a transmission scan with a cobalt-57 flood source had been performed to determine patient attenuation. Blood samples were taken every 10 min during the first hour after injection, and at about 4 and 20 h. Urine and faeces were collected during the first 20 h. Organ uptake was estimated after correction for body background activity, attenuation and scatter. Residence times were calculated from the dynamic and whole-body studies and used as input in the Mirdose 3.1 program to obtain organ doses and effective dose. It was found that radioactivity strongly accumulated in the kidneys and the liver [at 70 min p.i., 28% +/- 8% and 20% +/- 4% of the injected dose (ID), respectively]. Uptake in the target tissues (lymphomas or heart) was negligible from a dosimetric point of view. Extrapolating data from the first 20 h, one finds that approximately 73% of the ID will be excreted in the urine, and 27% in the faeces. The biological half-life of the activity in the total body was 16 +/- 7 h. Some organ doses +/- standard deviation (SD) in microGy/MBq were: kidneys 63 +/- 22, urinary bladder 20 +/- 6, spleen 15 +/- 3, liver 13 +/- 3, upper large intestine 12 +/- 6, lower large intestine 8 +/- 4, testes 6 +/- 2 and red bone marrow 4 +/- 0.7. The effective dose was 7.6 +/- 0.5 microSv/MBq, corresponding to a total effective dose of 4.6 +/- 0.3 mSv for a nominal injected activity of 600 MBq. In conclusion, 99mTc-Apomate has a high uptake in the kidneys and liver--in fact a factor of 1.3-1.6 higher than that found for the previously studied 99mTc-(n-1-imino-4-mercaptobutyl)-annexin-V. The biological half-life is shorter, however, but still long compared with the physical half-life of 99mTc. The faster appearance of activity in the intestines may preclude imaging of apoptosis in the abdomen. The effective dose is within the lower range of values reported for typical 99mTc compounds.

Effect of intraduodenal bile salt on pancreaticobiliary responses to bombesin and to cholecystokinin in humans

Bile salts modulate postprandial gallbladder emptying and pancreatic enzyme secretion, possibly by interfering with plasma cholecystokinin (CCK) responses. The regulatory role of bile salts in the absence of nutrients from the gut is poorly understood. Therefore, we studied the effect of intraduodenal sodium chenodeoxycholate on bombesin (BBS)- or CCK-stimulated plasma CCK levels, plasma pancreatic polypeptide levels, gallbladder motility, and pancreatic enzyme secretion. In a crossover design, saline without or with chenodeoxycholate was perfused intraduodenally for 3 hours in healthy volunteers. During the last hour, either BBS (n = 9) or CCK (n = 10) was infused intravenously. Chenodeoxycholate inhibited BBS-stimulated gallbladder emptying from 59% +/- 4% to 34% +/- 6% (P <.05) and intraduodenal bilirubin output from 41 +/- 9 to 21 +/- 5 micromol/h (P <.05), but it increased integrated plasma CCK levels from 157 +/- 19 to 184 +/- 19 pmol/L. 60 min (P =.01). Similarly, chenodeoxycholate administration inhibited gallbladder emptying and bilirubin output in response to intravenous CCK. Chenodeoxycholate also tended to reduce pancreatic polypeptide release and intraduodenal amylase output in response to intravenous BBS or CCK. It is concluded that intraduodenal chenodeoxycholate administration inhibits BBS- or CCK-stimulated gallbladder emptying, probably by diminishing target organ sensitivity to circulating CCK.

Plasma cholecystokinin and gallbladder responses to increasing doses of bombesin in celiac disease

Impaired postprandial gallbladder emptying in celiac disease has been attributed to an absence of appropriate cholecystokinin release. To determine if a flat jejunal mucosa in celiac patients is related to a reduced cholecystokinin-secreting capacity, increasing doses of bombesin were infused into six patients with celiac disease and a flat jejunal mucosa (group A), in seven celiac patients with a normal jejunal mucosa while on a gluten-free diet (group B), and in seven healthy controls (group C). Bombesin induced significant (P < 0.05) increments of plasma CCK to a maximum value of 1.0 +/- 0.3 pM in group A, to 1.5 +/- 0.3 pM in group B, and to 1.2 +/- 0.3 pM in group C (NS between groups), that were accompanied by significant (P < 0.05) gallbladder emptying responses of 70 +/- 4% in group A, 47 +/- 10% in group B and 65 +/- 5% in group C. Dose-response relationships were not different between groups. We conclude that there is no major impairment of gallbladder responsiveness to bombesin or of cholecystokinin-secreting capacity in patients with a flat jejunal mucosa due to celiac disease.

Inhibition of pancreaticobiliary secretion by loperamide in humans

Loperamide, a peripherally acting opiate receptor agonist with antidiarrheal action, inhibits ileal and colonic motor function. It was determined whether loperamide also affects gallbladder emptying and pancreatic enzyme secretion in humans. Plasma cholecystokinin (radioimmunoassay), gallbladder volume (ultrasonography), and intraduodenal bilirubin and amylase output (spot sampling) were measured at regular intervals before and during intraduodenal perfusion of an amino acid meal in 8 healthy subjects: once without and once with pretreatment of 8 mg loperamide, ingested 13 and 4 hours before the start of the meal. Loperamide decreased basal amylase output from 3.2 +/- 0.5 to 1.0 +/- 0.5 kU/h (P < .005) and abolished basal bilirubin output (21 +/- 5 vs. 0 +/- 0 micromol/h; P < .005) into the duodenum. Loperamide increased basal gallbladder volume from 28 +/- 4 to 39 +/- 4 mL (P < .0001) but was without effect on basal plasma cholecystokinin (2.7 +/- 0.3 vs. 3.0 +/- 0.3 pmol/L). During the amino acid meal, pretreatment with loperamide inhibited amylase output from 5.1 +/- 0.8 to 1.6 +/- 0.4 kU/h (P < .001), bilirubin output from 39 +/- 6 to 18 +/- 6 micromol/h (P < .0005) and gallbladder contraction from 47% +/- 3% to 26% +/- 6% (P < .05), whereas loperamide enhanced amino acid-stimulated plasma cholecystokinin from 4.5 +/- 1.6 to 7.6 +/- 1.0 pmol/L (P < .05). It is concluded that loperamide inhibits basal and amino acid-stimulated gallbladder motility and intraduodenal output of bilirubin and amylase, despite an enhanced postprandial cholecystokinin release.

Cholestyramine influences meal-stimulated pancreaticobiliary function and plasma cholecystokinin independent of gastric emptying and food digestion

BACKGROUND

Cholestyramine enhances gallbladder emptying and plasma cholecystokinin responses to oral ingestion of a mixed meal. It is not known whether this effect occurs independently of alterations in gastric emptying or maldigestion of nutrients.

METHODS

We perfused 15 g of an amino acid meal intraduodenally for 60 min in seven healthy volunteers, once with and once without cholestyramine. Intraduodenal perfusion of saline with or without cholestyramine (6 g/h) was started 60 min before the amino acid meal and continued for 2 h.

RESULTS

Cholestyramine markedly enhanced the incremental plasma cholecystokinin response to the meal from 36 +/- 12 to 139 +/- 25 pmol/l x 60 min (P < 0.005), incremental amylase output from 2.4 +/- 0.7 to 5.7 +/- 0.7 kU/h (P < 0.05), and incremental integrated gallbladder contraction from 1948 +/- 235 to 2840 +/- 189% x 60 min (P < 0.05).

CONCLUSION

The enhancing effect of cholestyramine on postprandial gallbladder contraction, pancreatic enzyme secretion, and plasma cholecystokinin release is not dependent on gastric emptying rates or appropriate digestion of nutrients.

Role of intraduodenal proteases in plasma cholecystokinin and pancreaticobiliary responses to protein and amino acids

BACKGROUND & AIMS

The role of small intestinal proteolytic activity in the regulation of upper gastrointestinal function in humans is poorly understood. The aim of this study was to determine the importance of proteolytic activity for protein- or amino acid-induced cholecystokinin release and pancreaticobiliary secretion.

METHODS

In 9 healthy subjects, saline was perfused intraduodenally for 3 hours either with or without the synthetic protease inhibitor camostate. During the last hour, albumin or amino acids in the same molecular composition as albumin were also perfused.

RESULTS

Perfusion with camostate, in concentrations that abolished intraduodenal proteolytic activity, had no effect on unstimulated plasma cholecystokinin concentrations or gallbladder emptying, but markedly (P < 0.05) increased unstimulated pancreatic enzyme output. Perfusion with protein distinctly stimulated cholecystokinin release, gallbladder emptying, and pancreatic enzyme output (P < 0.05). Perfusion with camostate resulted in significantly lower protein-stimulated plasma cholecystokinin, gallbladder, and pancreatic enzyme responses (P < 0.05). Perfusion with amino acids also stimulated plasma cholecystokinin, gallbladder emptying, and pancreatic enzyme output (P < 0.05). Camostate did not inhibit these values.

CONCLUSIONS

This study shows that appropriate digestion of protein is required to stimulate plasma cholecystokinin release, gallbladder emptying, and pancreatic enzyme secretion in humans.

Plasma cholecystokinin levels and gallbladder volumes after proctocolectomy with ileal pouch-anal anastomosis

BACKGROUND

The colon and rectum contain regulatory peptides in mucosal endocrine cells, which suggests a hormonal role. In animal studies colectomy leads to increased plasma levels of cholecystokinin. Little is known about the effects of proctocolectomy with ileal pouch-anal anastomosis on the release of cholecystokinin in human beings. Therefore we studied the effects of this procedure on fasting, postprandial, and bombesin-stimulated plasma cholecystokinin levels and gallbladder volumes.

METHODS

Ten patients who had undergone proctocolectomy with ileal pouch-anal anastomosis and 12 healthy volunteers participated in the study. Fasting and postprandial plasma cholecystokinin levels and gallbladder volumes were studied for 3 hours at 15-minute intervals. In a second experiment plasma cholecystokinin levels were measured before and during intravenous administration of bombesin in six patients with ileal pouch and five healthy volunteers.

RESULTS

Fasting plasma cholecystokinin levels were higher (p < 0.05) in patients with ileal pouch-anal anastomosis (2.6 +/- 0.3 pmol/L) compared with controls (1.7 +/- 0.2 pmol/L). Integrated postprandial plasma cholecystokinin levels were also distinctly higher (p < 0.01) in patients (978 +/- 126 pmol/L.180 min) than in controls (588 +/- 60 pmol/L.180 min). Mean fasting gallbladder volume was significantly (p < 0.01) decreased in patients with ileal pouch-anal anastomosis (18 +/- 2 ml) compared with controls (28 +/- 2 ml). Postprandial gallbladder emptying as measured by percentage change was similar in both groups. After infusion of bombesin, integrated plasma cholecystokinin responses were higher (p < 0.05) in patients (161 +/- 20 pmol/L.20 min) than in controls (90 +/- 12 pmol/L.20 min).

CONCLUSIONS

Fasting, postprandial, and bombesin-stimulated plasma cholecystokinin levels are elevated in patients with ileal pouch-anal anastomosis compared with controls. Fasting gallbladder volume is decreased after ileal pouch-anal anastomosis. These findings suggest that the colon contains a factor that inhibits the release of cholecystokinin.

Effect of bile salt binding or protease inactivation on plasma cholecystokinin and gallbladder responses to bombesin

BACKGROUND/AIMS

Bombesin-stimulated plasma cholecystokinin levels decrease after an initial increase despite continuous infusion of bombesin. The aim of this study was to determine if a feedback mechanism, mediated by bile salts or proteolytic enzymes, is responsible for this decline.

METHODS

Bombesin (1.0 ng.kg-1.min-1) was infused into volunteers for 180 minutes on separate occasions. Cholestyramine, colestipol, camostate, or saline were perfused intraduodenally during the second hour of the tests. Cholestyramine was also administered without infusion of bombesin.

RESULTS

Colestipol and cholestyramine, dependent on their bile salt-binding capacity, markedly enhanced (P < 0.05) bombesin-stimulated plasma cholecystokinin from 2.1 +/- 0.5 pmol/L to 6.4 +/- 2.2 pmol/L and 12.1 +/- 3.3 pmol/L (P < 0.05 vs. colestipol), respectively, and further decreased gallbladder volume (P < 0.05) from 9.4 +/- 1.6 mL to 2.0 +/- 0.4 mL and 2.2 +/- 0.5 mL, respectively. The protease inhibitor camostate had no effect. Bile salt precipitation also enhanced plasma pancreatic polypeptide responses (P < 0.01) but did not alter gastrin responses. Plasma cholecystokinin responses to cholestyramine without bombesin infusion varied considerably, but increments were highly correlated to decreases in gallbladder volume (r = 0.91; P < 0.005).

CONCLUSIONS

Bile salt sequestration but not protease inactivation enhances plasma cholecystokinin and gallbladder responses to bombesin infusion in humans.