Effects of cholecystokinin receptor antagonist loxiglumide on rat exocrine pancreas

Effect of endogenous cholecystokinin on the course of acute pancreatitis in rats

AIM: To examine the effects of pancreatic rest, stimulation and rest/stimulation on the natural course of recovery after acute pancreatitis.

METHODS: Acute hemorrhagic pancreatitis (AP) was induced in male rats by intraductal infusion of 40 μL/100 g body weight of 3% sodium taurocholate. All rats took food ad libitum. At 24 h after induction of AP, rats were divided into four groups: control (AP-C), pancreas rest (AP-R), stimulation (AP-S), and rest/stimulation (AP-R/S). Rats in the AP-C, AP-R and AP-S groups received oral administration of 2 mL/kg body weight saline, cholecystokinin (CCK)-1 receptor antagonist, and endogenous CCK release stimulant, respectively, twice daily for 10 d, while those in the AP-R/S group received twice daily CCK-1 receptor antagonist for the first 5 d followed by twice daily CCK release stimulant for 5 d. Rats without any treatment were used as control group (Control). Biochemical and histological changes in the pancreas, and secretory function were evaluated on day 12 at 24 h after the last treatment.

RESULTS: Feeding ad libitum (AP-C) delayed biochemical, histological and functional recovery from AP. In AP-C rats, bombesin-stimulated pancreatic secretory function and HOMA-β-cell score were significantly lower than those in other groups of rats. In AP-R rats, protein per DNA ratio and pancreatic exocrine secretory function were significantly low compared with those in Control rats. In AP-S and AP-R/S rats, the above parameters recovered to the Control levels. Bombesin-stimulated pancreatic exocrine response in AP-R/S rats was higher than in AP-S rats and almost returned to control levels. In the pancreas of AP-C rats, destruction of pancreatic acini, marked infiltration of inflammatory cells, and strong expression of α-smooth muscle actin, tumor necrosis factor-α and interleukin-1β were seen. Pancreatic rest reversed these histological alterations, but not atrophy of pancreatic acini and mild infiltration of inflammatory cells. In AP-S and AP-R/S rats, the pancreas showed almost normal architecture.

CONCLUSION: The favorable treatment strategy for AP is to keep the pancreas at rest during an early stage followed by pancreatic stimulation by promoting endogenous CCK release.

Effects of protease inhibitor ONO-3403 on pancreatic exocrine response to CCK in rats

AIM

To examine the pancreatic exocrine response to CCK-8 and to clarify the mechanism of the pancreatic exocrine hypersecretion after oral administration of synthetic protease inhibitor ONO-3403 in rats.

METHODS

A single oral dose of synthetic protease inhibitor ONO-3403 was given to rats by orogastric tube 6h and 12 h before experiments. The pancreatic juice was collected before test and after stimulation of stepwise increasing doses of CCK-8. The output of protein, amylase, lipase and bicarbonate in pancreatic juice or pancreatic tissue were determinated by Lowry method, Chromogenic method with blue-dyed starch polymer, Whitaker method and by the DST 800 multititration system, respectively.

RESULTS

Oral administration of ONO-3403 had no influence on pancreatic juice flow and output of protein in basal and CCK-8 stimulation at 6h after ONO-3403 pretreated, but it caused a significant increase in pancreatic juice flow (peak level 215±9 ulper 30 min vs 93±6 ulper 30 min, P<0.01) and protein output (peak level 16475±1 801 ug per 30 min vs 5 920±593 ug per 30 min, P<0.01) of the basal and CCK-8 stimulation at 12 h after ONO-3 403 pretreated. The basal pancreatic juice flow and output of amylase (470±32 su per 30 min at 6 h P<0.01, 394±47 su per 30 min at 12 h, P<0.05 vs 251±32 su per 30 min), bicarbonate (2.224±0.333 umolper 30 min at 6 h, P<0.05; 3.148±0.374 umolper 30 min at 12 h, P<0.01 vs 1.428±0.282 umolper 30 min) were significant high after ONO-3403 pretreated than those of control group. There was no change in lipase output compared with control group. The pancreatic weight, pancreatic contents of protein and amylase in ONO-3 403 pretreated rats were similar to those in control rats.

CONCLUSION

ONO-3 403 can increase pancreatic exocrine secretion and sensitivity to CCK-8 stimulation.The mechanism of ONO3 403 induced pancreatic exocrine hypersecretion may be a feedback regulation of the pancreas by increasing CCK secretion.

Troglitazone stimulates pancreatic growth in congenitally CCK-A receptor-deficient OLETF rats

We examined the effect of troglitazone treatment on pancreatic growth in the CCK-A receptor-deficient Otsuka Long-Evans Tokushima fatty (OLETF) rat, an animal model for type 2 diabetes mellitus. A troglitazone-rich diet (0.2%) was given from 12 to 28 wk of age or from 12 or 28 wk of age to 72 wk of age. Fasting serum glucose concentrations in control OLETF rats increased progressively with age, which was almost completely prevented by troglitazone treatment. Insulin levels in serum and pancreatic content in the control rat markedly increased at 28 wk of age but significantly decreased at 72 wk of age compared with those at 12 wk of age, whereas those in troglitazone-treated rats were nearly the same at all ages and were similar to those in control rats at 12 wk of age. Pancreatic wet weight in control rats decreased with age irrespective of whether they were hyperinsulinemic (28 wk old) or hypoinsulinemic (72 wk old). Troglitazone treatment significantly increased pancreatic wet weight and protein, DNA, and enzyme contents compared with those in the control rats. Moreover, troglitazone treatment completely prevented or reversed histological alterations such as fibrosis, fatty replacement, and inflammatory cell infiltration. Our results indicate that troglitazone stimulates pancreatic growth in the congenitally CCK-A receptor-deficient OLETF rat not only by reducing insulin resistance and potentiating insulin action but also by suppressing inflammatory changes in the pancreas.

CCK-, secretin-, and cholinergic-independent pancreatic fluid hypersecretion in protease inhibitor-treated rats

Plasma cholecystokinin (CCK) levels in fed rats increased from 2.59 +/- 0.13 pmol/l to the peak of 27.6 +/- 4.1 pmol/l at 1 h after a single oral administration of synthetic protease inhibitor (PI; ethyl N-allyl-N-[(E)-2-methyl-3-[4-(4-amidino-phenoxycarbonyl)phenyl] propenoyl] amino acetate methansulfonate; 20 mg/kg body wt), but then returned to the preloading value at 12 h after administration. The pancreatic fluid secretion, rich in chloride but poor in bicarbonate, was significantly elevated at 6-12 h postfeeding (100.9 +/- 8.2 vs. 27.3 +/- 2.3 microliters/30 min in control rats, P < 0.01). Loxiglumide (50 mg.kg body wt-1.h-1), atropine (100 micrograms.kg body wt-1.h-1), or antisecretin serum (100 microliters/rat) at 12 h postfeeding did not modify the fluid hypersecretion. Loxiglumide, when given together with PI, completely abolished fluid hypersecretion, but it could not inhibit hypersecretion when applied 3 h after PI treatment. Labeling with 5-bromo-2'-deoxyuridine showed active proliferation of acinar cells at 3 h after PI treatment (3.56 +/- 0.29% vs. 0.46 +/- 0.08% in control, P < 0.001), but not in rats given loxiglumide together with PI. In rats that fasted from 12 h before to 12 h after PI feeding, neither pancreatic fluid hypersecretion nor active proliferation of acinar cells was observed. These results suggest that pancreatic fluid hypersecretion in fed rats at 6-12 h after PI treatment is caused not by CCK-, secretin-, or cholinergic-dependent mechanisms but probably by acinar cell proliferation.

Effect of chronic oral administration of the CCK receptor antagonist loxiglumide on exocrine and endocrine pancreas in normal rats

CONCLUSION

In normal adult rats, administration of a low dose of loxiglumide for 7 d had no significant effect on exocrine and endocrine pancreatic function, whereas a high dose of loxiglumide decreased pancreatic enzyme output without inducing insulin resistance and diabetes mellitus.

BACKGROUND

There is a possibility that chronic administration of cholecystokinin receptor antagonists not only inhibits the growth of the pancreas but also alters exocrine and endocrine pancreatic function.

METHODS

Loxiglumide at a dose of 50, 100, or 200 mg/kg body weight, or the same volume of saline, was given by an orogastric tube twice daily for 7 d (13 successive times). Biochemical and functional changes were determined on d 8 at 24 h after the last administration of loxiglumide and 18 h fasting. Pancreatic exocrine and endocrine function was simultaneously determined following an intravenous injection of a mixed solution of 0.5 g/kg body weight glucose plus 100 ng/kg body weight cerulein.

RESULTS

Pancreatic weight and protein content were dose-dependently decreased by loxiglumide, whereas DNA content was decreased only by the highest dose of loxiglumide. Loxiglumide caused dose-dependent decreases in pancreatic fluid and protein output. Total pancreatic insulin content in rats treated with loxiglumide was not significantly different from that in the control rats. However, insulin concentration relative to DNA content was significantly increased in rats treated with 200 mg/kg body weight loxiglumide compared with that in other groups of rats. Glucose-stimulated insulin release was significantly low in rats treated with the highest dose of loxiglumide compared with that in other groups of rats, although there was no difference of serum glucose concentrations among these four groups of rats.

Gastric gland degeneration induced in monkeys by the CCK-B/gastrin receptor antagonist CI-988

Gastric effects of subchronic treatment with the cholecystokinin-B (CCK-B)/gastrin receptor antagonist CI-988 were investigated in cynomolgus monkeys. In preliminary range-finding studies, CI-988 was given orally to 1 monkey per sex for 14 days at doses of 50, 100, 200, and 500 mg/kg/day. Subchronic studies of CI-988 were subsequently conducted using 5 monkeys per sex at doses of 0, 5, 25, and 75 mg/kg for 4 or 13 wk. High-dose monkeys were dosed initially at 100 mg/kg, but the dose was not well tolerated and was decreased to 75 mg/kg after 8 days of treatment. One male monkey at 75 mg/kg was euthanatized in extremis on day 23. In the range-finding study, minimal to moderate, multifocal to diffuse degeneration of gastric glands, primarily in the fundic region, was observed at 100 mg/kg and above, with frank gastric mucosal atrophy occurring at 200 and 500 mg/kg. Minimal to mild gastric gland degeneration was also observed in the subchronic study after 4 wk at 25 and 75 mg/kg, but histopathologic gastric changes were remarkably absent after 13 wk. Mucosal height in the stomach fundus was decreased 19.8% in 75-mg/kg males at week 4, and although gastric mucosa appeared histologically normal after 13 wk, mucosal height remained 28.6% less than that of controls. In females at 75 mg/kg, fundic mucosal height was decreased 7% and 5% at weeks 4 and 13, respectively, but decreases were not statistically significant. Mean serum gastrin concentrations were increased 10-fold in males only after 4 wk at 75 mg/kg, but were comparable to controls during week 13. CI-988-induced gastric gland degeneration is consistent with antagonism of gastrin's trophic activity toward gastric mucosa. Notwithstanding decrements in gastric mucosal height, disappearance of mild histopathologic findings despite continued treatment with the ligand suggests some degree of adaptation to subchronic CCK-B/gastrin inhibition, although the mechanism of accommodation has yet to be delineated.

Loss of sensitivity to cholecystokinin stimulation of isolated pancreatic acini from genetically diabetic rats

Pancreatic exocrine function of a new inbred strain Otsuka Long-Evans Tokushima Fatty (OLETF) rat that develops spontaneous persistent hyperglycemia was evaluated in in vitro isolated pancreatic acini and compared with that in the control Long-Evans Tokushima Otsuka (LETO) rat. Serum glucose and insulin concentrations in the OLETF rats were significantly high (glucose: 270 +/- 12 vs. 208 +/- 10 mg/100 ml, P < 0.01; insulin: 12.4 +/- 1.7 vs. 4.9 +/- 0.6 ng/ml, P) < 0.01), whereas pancreatic wet weight was significantly low (803 +/- 20 vs. 1,138 +/- 17 mg, P < 0.01) compared with those in the LETO rat. Pancreatic acini isolated from the OLETF rat were totally insensitive to cholecystokinin (CCK)-8 stimulation at concentrations of up to 100 nM. However, neither the responsiveness nor the sensitivity to carbamylcholine, bombesin, and secretin of the acini from the OLETF rat was altered or even increased, probably due to the larger amylase content in the OLETF rat acini compared with those of the LETO rat acini (31.5 +/- 2.0 vs. 13.0 +/- 1.1 Somogyi units/micrograms DNA, P < 0.01). The responsiveness to fluoride, a direct activator of guanine nucleotide-binding protein, in the OLETF rat acini was similar to that in the LETO rat, suggesting that the transmembrane signaling and effectors and subsequent intracellular signal transduction molecules in the OLETF rat acini are normal. Moreover, 125I-CCK binding to the acini prepared from the OLETF rat was totally absent. These present results indicate that the OLETF rat has a selective defect in the binding of CCK to its receptors on the acinar cell surface.

Treatment with cholecystokinin receptor antagonist loxiglumide enhances insulin response to intravenous glucose stimulation in postpancreatitic rats

Pancreatic exocrine and endocrine function in postpancreatitic rats treated with cholecystokinin (CCK) receptor antagonist loxiglumide was compared with that treated with saline and CCK octapeptide (CCK-8) or with that in normal control rats. Treatment with loxiglumide (50 mg/kg body weight), CCK-8 (2.5 micrograms/kg body weight), or saline (2.5 ml/kg body weight) was given three times a day for 6 days starting 1 day after the induction of acute pancreatitis by a 4-h subcutaneous infusion of 20 micrograms/kg body weight/h of caerulein. On day 8, pancreatic exocrine and endocrine function was simultaneously determined following an intravenous injection of a mixed solution of 0.2 g/kg body weight glucose plus 100 ng/kg body weight caerulein. Basal pancreatic juice flow was significantly increased in all of the postpancreatitic rats irrespective of the treatment, whereas the maximal juice flow in the loxiglumide- and saline-treated rats was significantly low compared with the CCK-8-treated and the control rats. Basal and the peak protein outputs in the loxiglumide-treated rats were comparable to those in saline-treated rats, but were lower than those in the control or the CCK-8-treated rats. Although serum glucose concentrations in all of the postpancreatitic rats were similar to those in the control rats, stimulated as well as basal insulin release tended to be high compared with the control rats. In particular, loxiglumide-treated rats showed the exaggerated insulin response compared with other groups of rats. These present observations indicate that administration of high dose of loxiglumide for a long period decreases pancreatic enzyme output and causes insulin resistance.