Basal Amylase Secretion Research Articles

Secretagogue response of azaserine-induced rat pancreatic acinar tumors in vivo

This study investigates digestive and lysosomal enzyme secretion of azaserine-induced pancreatic acinar carcinomas in response to cholecystokinin in rats. After 15–20 months of treatment, 95% of the animals developed pancreatic acinar carcinomas encompassing more than 90% of the tissue. In anesthetized rats basal trypsin output was significantly elevated in the tumor group despite diminished fluid secretion. There was a linear correlation between tumor size and basal amylase and trypsin secretion. Intravenous infusion of cholecystokinin (25 IDU · kg−1 · h−1) induced a significantly lower secretion of fluid per gram pancreas, as well as decreased amylase and trypsin output, in the tumor group compared with the control group. Plasma amylase and lipase levels were significantly elevated in the tumor group under both basal and stimulated conditions. The output of the lysosomal enzymes β-d-glucuronidase and α-d-glucosidase was significantly increased in the tumor group under background secretin infusion. Additional cholecystokinin infusion caused a sharp increase in glucuronidase output in this group with only minimal increase in controls. Glucosidase output increased similarly in both groups. Amylase, lipase, and trypsin tumor tissue concentrations were markedly reduced by 85%, 90%, and 87%, respectively. It was concluded that the decreased secretory response of digestive enzymes may result from decreased synthesis, lowered storage capabilities, and/or a decreased/increased responsiveness to cholecystokinin. Increased glucuronidase secretion may reflect an augmented cell turnover of malignant tissue.

Prostaglandin E2 inhibits secretagogue-induced enzyme secretion from rat pancreatic acini

Prostaglandins of the E type may have a potential role in pancreatic physiology and pathophysiology. Because prostaglandins of the E type inhibit HCl secretion in parietal cells via a specific receptor by inhibition of adenylylcyclase, we studied whether a similar mechanism exists in the exocrine pancreas. Isolated rat pancreatic acini were incubated with various concentrations of secretagogues, such as cholecystokinin-octapeptide (CCK-8), bombesin, carbachol, and vasoactive intestinal peptide (VIP), in the absence or presence of prostaglandin E2 (PGE2), and amylase secretion was measured. For receptor binding studies, acini and pancreatic membranes were incubated with [3H]PGE2 and either unlabeled PGE2 or other types of prostaglandins. PGE2 (10(-13) to 10(-5) M) did not inhibit basal amylase secretion. However, CCK-8-stimulated secretion was significantly inhibited. Stimulation of secretion by bombesin, carbachol, VIP, and secretin was also inhibited by PGE2, but not as pronounced as CCK-8-stimulated secretion. The formation of inositol 1,4,5-trisphosphate induced by CCK-8 was markedly inhibited by simultaneous incubation with PGE2. Furthermore, PGE2 slightly but significantly reduced the CCK-8-induced efflux of 45Ca2+ from prelabeled acini. Intact acini and a membrane fraction bound [3H]PGE2 and this function could be equally competed by either unlabeled PGE2 or PGE1 in contrast to less-related prostaglandins such as PGF2 alpha, PGD2, and prostacyclin. We conclude that prostaglandins of the E type inhibit pancreatic enzyme secretion stimulated by various secretagogues. This function is mediated via specific receptors for PGE. With regard to CCK-8-stimulated secretion this function may be mediated by an inhibition of formation of inositol 1,4,5-trisphosphate.

THE EFFECT OF CYCLOSPORINE ON EXOCRINE FUNCTION OF THE RAT PANCREAS—AN IN VITRO STUDY

We have studied the effect of cyclosporine on the exocrine pancreas of rats submitted to treatment with different parenteral doses (15, 30, 50 mg/kg/day) for different time periods (7 and 30 days). Serum amylase levels, pancreas weight, and total pancreatic amylase and protein content showed a dose-dependent decrease. Basal amylase secretion from isolated lobules remained unchanged. Furthermore, the pancreatic lobules from animals under cyclosporine treatment exhibited a decreased response to bethanechol stimulation. Our data suggest that cyclosporine produces a toxic effect on exocrine pancreatic function.

Pancreatic function in the essential fatty acid deficient rat

The influence of essential fatty acid (EFA) deficiency on pancreatic endocrine and exocrine function was studied in 120-day-old rats. The plasma insulin response was determined after in vivo administration of glucose and arginine. The plasma glucagon response was assessed after infusion of arginine. Islet peptides were examined by immunocytochemistry. The exocrine function of pancreas was studied by amylase secretion in isolated pancreatic acinar cells after stimulation with the cholinergic agonist carbacholine chloride. The EFA-deficient (EFAD) rats showed higher basal plasma insulin concentrations and lower basal glucose levels than control rats ( P < .01 and P < .01, respectively). The plasma insulin response to glucose was potentiated in the EFAD rats ( P < .001). Both insulin and glucagon responses to arginine were normal. The isolated pancreatic acinar cells showed a low basal amylase secretion, but a normal response to carbacholine chloride. There were no overt morphological changes seen in the pancreas and the immunocytochemical staining pattern of insulin, glucagon, somatostatin, and pancreatic polypeptide cells did not differ from controls. The results of the study show that the secretory function of the endocrine and exocrine pancreas is operational in EFA deficiency. The EFA deficiency was accompanied by a basal hyperinsulinemia and hypoglycemia and an exaggerated insulin response to glucose, the pathophysiology of which has to be further studied.

Effects of L-364, 718 on Pancreatic Exocrine and Endocrine Secretion in the Rat

We examined the inhibitory effect of L-364,718, a nonpeptide cholecystokinin (CCK) antagonist, on CCK stimulation of pancreatic exocrine and endocrine secretion in both the isolated pancreatic acini and the isolated perfused pancreata of rats. In the isolated acini, L-364,718 inhibited CCK octapeptide (CCK-8)-stimulated amylase release and binding of 125I-CCK-8 in a dose-dependent manner without appreciable effects on the basal amylase secretion. L-364,718 also inhibited amylase release in response to caerulein and gastrin I, but had no effect on amylase release stimulated by other secretagogues or by agents bypassing receptors. Similarly, binding of N-methylscopolamine to pancreatic acini was not inhibited by L-364,718. In the isolated perfused pancreata, L-364,718 inhibited CCK-8-stimulated pancreatic exocrine secretion and insulin release. The inhibitory effects of L-364,718 were more potent for insulin release than for exocrine secretion and persisted even after the removal of L-364,718 infusion. These results clearly demonstrate that L-364,718 is a specific, potent, and prolonged antagonist of CCK's stimulatory actions on pancreatic acinar and B cells.

Effect of CCK antagonist L 364718 on meal-induced pancreatic secretion in rats

The specific cholecystokinin (CCK)-receptor antagonist L 364718 was used to examine the role of CCK in meal-induced pancreatic secretion. Unanesthetized rats with gastric, jugular vein, bilepancreatic, and duodenal cannulas were used; bile-pancreatic juice was recirculated. Basal amylase secretion (30% of maximal) was not inhibited by L 364718 doses of 0.5 or 2 mg/kg intravenously. L 364718 (0.02 to 2 mg/kg) caused dose-related inhibition of the maximal amylase response to CCK-8 (200 pmol.kg-1.h-1), with greater than 80% inhibition at doses greater than or equal to 0.5 mg/kg. L 364718 (0.5 mg/kg) shifted the dose-response curve to CCK-8 (25-3,200 pmol.kg-1.h-1) to the right (ED50 increased 10-fold) but did not alter maximal amylase output consistent with competitive inhibition of CCK in vivo. Ingestion of liquid food significantly increased amylase output threefold above basal. L 364718 (0.5 mg/kg) completely blocked this response. These results suggest that although CCK does not regulate basal pancreatic enzyme secretion, it is the primary mediator of pancreatic enzyme secretion in response to a liquid meal.

The effect of dimethyl PGE 2 on canine pancreatic autograft exocrine secretion

This study was designed to evaluate the effect of 16, 16-dimethyl prostaglandin E 2 (dimethyl PGE 2) on exocrine secretion in autografted animals with pancreaticocystostomies. The rates of secretion of urinary (autograft) amylase (units/min) and bicarbonate (mmole/min), over a 5-hr interval, were determined in the basal state (Group A, N = 5), after a bolus injection of 1 μg/kg of dimethyl PGE 2 (Group B, N = 5), during an OP-CCK infusion at 125 ng/kg/hr (Group C, N = 5), and during an OP-CCK infusion plus a bolus injection of 1 μg/kg (Group D, N = 5) or 18 μg/kg (Group E, N = 5) of dimethyl PGE 2 at the end of the second hour. Basal secretion of amylase and bicarbonate were decreased 1 hr after 1 μg/kg of dimethyl PGE 2, with the bicarbonate inhibition being statistically significant (Group A = 0.073 ± 0.04 vs Group B = 0.001 ± 0.00; P < 0.05). When compared to Group C (128.3 ± 28.0), an immediate and significant inhibition of OP-CCK-stimulated amylase release was demonstrated in both Group D (36.3 ± 11.1; P < 0.02) and Group E (57.3 ± 13.4; P < 0.05). One and two hours post-dimethyl PGE 2, amylase releases were 37.7 ± 8.6 and 64.7 ± 6.8 in Group D and 0.92 ± 0.3 and 8.28 ± 2.6 in Group E, compared to 140.3 ± 23.3 and 104.9 ± 31.8 in Group C, indicating a dose-related, prolonged inhibition of autograft amylase secretion. Bicarbonate secretions immediately and at 1 and 2 hr post-dimethyl PGE 2 were 0.04 ± 0.01, 0.00 ± 0.00, and 0.03 ± 0.01 in Group D and 0.04 ± 0.01, 0.00 ± 0.00, and 0.01 ± 0.00 in Group E, compared to 0.05 ± 0.01, 0.07 ± 0.03, and 0.05 ± 0.02 in Group C. Significant inhibition was present, in both Groups D and E at 1 hr postinfusion only, indicating more transient inhibition of autograft bicarbonate secretion. These studies demonstrate that dimethyl PGE 2 has an inhibitory effect on basal and OP-CCK-stimulated exocrine secretion in a denervated, autograft model. Although the mechanism of inhibition remains to be elucidated, the therapeutic potential of dimethyl PGE 2 in reducing post-transplant exocrine complications warrants further evaluation.

Altered exocrine pancreatic function in rats treated with nicotine

The present study investigates the effects of nicotine treatment on exocrine pancreatic function. Adult male, Sprague-Dawley rats received nicotine via a time-release pellet, at a rate of 1.65 μg/min for 3 weeks. At the end of the experimental period, it was observed that although nicotine did not affect final body or pancreatic weight, the activities of amylase, trypsin, and chymotrypsin in pancreatic homogenates from nicotine-treated rats were 51, 29, and 35% higher, respectively, than in controls. Levels of immunoreactive cationic trypsin(ogen) were significantly higher in pancreatic homogenates and serum from nicotine-treated rats as compared with controls. In addition, concentrations of mRNA, encoding for pancreatic amylase, were higher in pancreatic homogenates from the nicotine-treated rats than in controls. In dispersed pancreatic acini isolated from nicotine-treated rats, basal secretion of amylase, trypsinogen, and chymotrypsinogen was 50% higher than controls and enzyme release following CCK-8 (100 p m), secretin (1 μ m), and carbachol (7.5 μ m) stimulation was also significantly higher. These dat indicate that nicotine treatment, at levels comparable to those expected in moderate cigarette smokers, increases the content of digestive enzymes in rat pancreas, as well as their basal and secretagogue-induced release.

Galanin Inhibits Amylase Secretion from Isolated Rat Pancreatic Acini

The neuropeptide galanin is present in intrapancreatic nerve fibers and is known to affect the secretion of the islet hormones. Its most potent effect is thereby the inhibition of insulin secretion. In the present study, we investigated whether galanin influences amylase secretion from isolated rat pancreatic acini. Acini were isolated by the collagenase digestion technique and incubated for 45 min in a Krebs-Henseleit medium with or without addition of the cholinergic agonist carbachol or the C-terminal octapeptide of cholecystokinin (CCK-8) in the presence or absence of galanin. Carbachol, at its optimal concentration (10(-5) M), stimulated amylase secretion to 11.8 +/- 0.5% of total amylase content compared to 4.3 +/- 0.3% in controls (p less than 0.001). Galanin, (10(-8)-10(-9) M), reduced the carbachol-induced amylase secretion to 10.4 +/- 0.3% (p less than 0.01). Galanin at concentration levels below 10(-10) M had no significant effect. At 10(-8) M, CCK-8 stimulated amylase secretion to 9.7 +/- 0.6% compared with 5.2 +/- 0.3% in controls (p less than 0.01). Galanin (10(-7) M) reduced this stimulation to 8.0 +/- 0.4% (p less than 0.05). Galanin did not affect basal amylase secretion. It is concluded that the intrapancreatic neuropeptide galanin weakly inhibits carbachol- and CCK-8-induced amylase secretion from isolated rat pancreatic acini. Thus, galanin has the capability to directly affect not only endocrine but also exocrine pancreatic secretion although its effect of inhibiting amylase secretion seems weak.

BAY-K-8644-stimulated amylase secretion from pancreatic acinar cells

Pancreatic acinar cells do not contain depolarization-sensitive calcium channels. Nonetheless, in the current study, the calcium channel activator, BAY-K-8644, was found to stimulate a time- and concentration-dependent increase in the spontaneous release of amylase. Secretion was dependent on the presence of extracellular calcium in the incubation medium. Racemic BAY-K-8644 and (or) its S(-)optical isomer did not enhance the secretory response to either carbachol or cholecystokinin octapeptide; however, when co-applied with either phorbol ester, vasoactive intestinal peptide, or forskolin, they potentiated amylase secretion. Nifedipine and the R(+)isomer of BAY-K-8644, which are both calcium channel antagonists, did not alter basal or forskolin-stimulated amylase secretion, and [3H]nitrendipine did not bind to acinar cell membranes. Neither atropine nor dibutyryl cGMP, inhibitors of cholinergic and cholecystokininergic receptors, respectively, affected BAY-K-8644-induced amylase secretion. While BAY-K-8644 stimulated concentration-dependent cGMP synthesis in acinar cells, it had no effect on basal or forskolin-stimulated cAMP formation. The data suggest that BAY-K-8644 may bind to acinar cell sites that are not functional calcium channel proteins but are coupled nevertheless to the secretory response, and that calcium channel antagonists do not bind to these sites. The mechanism of the secretagogue action of BAY-K-8644 remains to be elucidated.

Phorbol ester inhibits cholecystokinin octapeptide-induced amylase secretion and calcium mobilization, but is without effect on secretagogue-induced hydrolysis of phosphatidylinositol 4,5-bisphosphate in rabbit pancreatic acini

The effect of prolonged protein kinase C activation on cholecystokinin octapeptide (CCK-8)-induced amylase secretion from rabbit pancreatic acini was studied by means of the phorbol ester, 12- O-tetradecanoylphorbol 13-acetate (TPA). The phorbol ester itself increased basal amylase secretion but inhibited completely the secretory response to relatively low concentrations of CCK-8. The inhibitory action of TPA on CCK-8-induced amylase secretion was paralleled by inhibition of CCK-8-induced calcium mobilization but not by inhibition of CCK-8-induced breakdown of 32P-labelled phosphatidylinositol 4,5-bisphosphate. The results presented suggest that protein kinase C, or one of its phosphorylated products, inhibits the CCK-8-stimulated pathway leading to secretion at a level beyond the secretagogue-induced hydrolysis of phosphatidylinositol 4,5-bisphosphate. Inhibition of the initial, inositol 1,4,5-trisphosphate-mediated and extracellular calcium-independent, increase in free cytosolic calcium concentration, together with the findings of others, suggests that the efficacy of this inositolphosphate to release calcium is reduced.

Pertussis toxin stimulates cholecystokinin-induced cyclic AMP formation but is without effect on secretagogue-induced calcium mobilization in exocrine pancreas

The role of a pertussis toxin sensitive GTP-binding protein in mediating between cholecystokinin receptors and phosphatidylinositol 4,5-bisphosphate phosphodiesterase as well as in preventing cholecystokinin from increasing cellular cyclic AMP has been investigated using dispersed acini from rabbit pancreas. Pertussis toxin pretreatment (500 ng/ml, 2 h) did not affect cholecystokinin(octapeptide) (CCK-8) -induced increases in cytosolic free Ca 2+ as judged from changes in fluorescence obtained from quin2-loaded acini. Although pretreatment with pertussis toxin was also without effect on resting acinar cell cyclic AMP levels, adenylate cyclase activity was increased, since inhibition of cyclic AMP phosphodiesterase activity by isobutylmethylxanthine (IBMX) resulted in an additional increase in cyclic AMP levels in toxin-treated acini, indicating that acinar cell adenylate cyclase activity is under some tonic inhibitory control by the pertussis toxin-sensitive inhibitory GTP-binding protein (G i) of the adenylate cyclase system. CCK-8 gave an increase in cyclic AMP levels in both control (1.6-fold) and toxin-treated (2.3-fold) acini, leading to cyclic AMP levels in the toxin-treated acini 2-times as high as those in control acini. In the presence of IBMX, the cyclic AMP response to CCK-8 was again markedly enhanced in acini pretreated with the toxin (3.2- vs. 1.8-fold), resulting in cAMP levels in the toxin-treated acini 3.7-times those in the absence of IBMX, 2.5-times those in control acini in the presence of IBMX and 7.0-times those in control acini in the absence of IBMX. Neither the pretreatment with pertussis toxin, nor the presence of IBMX alone, nor the combination had an effect on basal amylase secretion. However, all three treatments potentiated the stimulatory effect of CCK-8 on amylase secretion and the amount of potentiation was proportional to the cyclic AMP levels reached. Our findings suggest that in the intact pancreatic acinar cell G i inhibition of the catalytic subunit of the adenylate cyclase may largely be responsible for preventing cholecystokinin from increasing cellular cyclic AMP. They moreover show that cyclic AMP is a modulatory agent in rabbit pancreatic enzyme secretion, not able to stimulate secretion itself, but potentiating effects mediated by the phosphatidylinositol-calcium pathway.

CR-1409

The effects of a new glutaramic acid derivative, 3,4-dichloro-benzamido-N, N-dipentyl-glutaramic acid (CR-1409), on cholecystokinin-stimulated amylase release and 125I-cholecystokinin octapeptide binding were studied in isolated rat pancreatic acini. CR-1409 at concentrations between 0.3 and 30 microM inhibited cholecystokinin-stimulated amylase release in a dose-dependent manner without appreciable effect on the basal amylase secretion. Biphasic dose-response curves to cholecystokinin for amylase release shifted to the right with an increase in the concentration of the drug. IC50 (half-maximal inhibitory concentration) of CR-1409 for cholecystokinin-stimulated amylase release was 0.64 microM, and the potency of this drug on the inhibition of amylase release was 3400 times greater than that of proglumide. The effect of CR-1409 was rapid, reversible, and selective for cholecystokinin. In addition, CR-1409 at concentrations between 0.1 and 30 microM inhibited 125I-cholecystokinin octapeptide binding to rat pancreatic acini. IC50 of CR-1409 for 125I-cholecystokinin octapeptide binding was 0.22 microM, and the potency of this drug on the effect was 5900 times greater than that of proglumide.

Effect of short- and long-term alcohol feeding in rats on pancreatic enzyme content and enzyme secretion in isolated pancreatic lobules in vitro

The effect of short- and long-term ethanol intake on digestive enzyme secretion was determined in isolated pancreatic lobules of rats. Groups of male Wistar rats were fed a modified Lieber-DeCarli diet containing either 5% (w/v) of ethanol, isocaloric amounts of a liquid diet in which ethanol was substituted by starch, or solid rat chow; for 3 days, 1, 2, 4, 8 and 12 weeks. Basal and caerulein-stimulated secretion of lipase, amylase, chymotrypsin and trypsin and the enzyme content in the tissue were studied. Feeding the liquid control diet decreased the tissue content of the four enzymes as compared with the values obtained in the group receiving solid rat chow. While basal and stimulated amylase secretion was markedly reduced in the former group, the secretion pattern of the other enzymes exhibited only transient changes. Caerulein-stimulated secretion of lipase and the proteases was increased by ethanol, the effect being more pronounced during the initial phase of the experiment. Alcohol feeding stimulated the basal secretion of these enzymes only in weeks 1-4. In contrast to the other enzymes, basal and stimulated amylase secretion was not enhanced by ethanol feeding. The results suggest that the enzyme secretion of the rat pancreas is distinctly altered by chronic ethanol feeding. However, the response of the pancreatic enzymes is non-parallel, and changes with the duration of alcohol intake.

Morphological and biochemical changes of the pancreas in rats treated with acetaldehyde

Daily intraperitoneal injections of acetaldehyde for 10 days to adult rats produced distinct morphological and biochemical changes in the exocrine pancreas, without affecting the body weight, pancreatic weight, and DNA, RNA, and protein content of the pancreas. By electronmicroscopy, although the number and size of the acinar zymogen granules appeared to be the same between the saline- and acetaldehyde-treated rats, the zymogen granules of the latter group showed decreased osmiophilia. Acinar mitochondria of the acetaldehyde-treated rats were found to be slightly swollen with dense granules, and plasma membrane fragments were often seen in the acinar lumen. Administration of acetaldehyde significantly decreased immunoreactive cationic trypsin (ogen) and total amylase activity in the pancreas, but not in the serum, where amylase activity was markedly increased. Basal secretion of amylase, trypsinogen, and chymotrypsinogen from isolated dispersed pancreatic acini of acetaldehyde-treated rats was increased by 40-50%. Nicotine (5-25 mM) induced a profound increase in secretion of the same enzymes from isolated acini of both saline- and acetaldehyde-treated rats, but in the latter group there was a concomitant rise in LDH release. Furthermore, CCK-8 (1 nM), secretin (1 microM), and carbachol (10 microM) either alone or in combination with nicotine (12.5 mM) produced a profound stimulation in amylase, trypsinogen, and chymotrypsinogen secretion from acini of both groups of rats. On the other hand, secretion of 3H-pulse-labeled proteins from isolated acini of acetaldehyde-treated rats by nicotine was decreased by approximately 50% compared with the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of extracellular digestive enzymes to alter in vitro secretion by rat pancreas

The basal rate of amylase secretion from rat pancreatic lobules was found to diminish with time. This decline, which is not due to depletion of amylase stores or loss of tissue integrity, has been attributed to the build-up of amylase in the extracellular space [Ho and Rothman, Am. J. Physiol. 245 (Cell Physiol. 14): C21-C27, 1983]. This accumulation of amylase would result in a decrease in the intracellular-extracellular amylase gradient, which, according to the so-called equilibrium hypothesis, is responsible for net amylase secretion under basal conditions. Using rat pancreatic lobules and acini, we have tested the validity of this hypothesis by adding to the incubation medium at the onset of incubation either collected secretory products or purified amylase. Based on the equilibrium hypothesis, one would have predicted that these additions would also reduce the concentration gradient favoring net secretion and would result in an apparent reduction in the initial rate of basal in vitro digestive enzyme secretion. The results obtained from these studies, however, were not in accord with those predictions, since these additions did not diminish the initial rate of basal amylase secretion. Our observations therefore indicate that the decrease in the rate of basal amylase secretion from rat pancreas with time is not due to the loss of a concentration gradient favoring efflux. These results argue against the validity of the equilibrium hypothesis.

Glucocorticoids increase cholecystokinin receptors and amylase secretion in pancreatic acinar AR42J cells.

We recently reported in AR42J pancreatic acinar cells that glucocorticoids increased the synthesis, cell content, and mRNA levels for amylase (Logsdon, C.D., Moessner, A., Williams, J.A., and Goldfine, I.D. (1985) J. Cell Biol. 100, 1200-1208). In addition, in these cells glucocorticoids increased the volume density of secretory granules and rough endoplasmic reticulum. In the present study we investigate the effects of glucocorticoids on the receptor binding and biological effects of cholecystokinin (CCK) on AR42J cells. Treatment with 10 nM dexamethasone for 48 h increased the specific binding of 125I-CCK. This increase in binding was time-dependent, with maximal effects occurring after 48 h, and dose-dependent, with a one-half maximal effect elicited by 1 nM dexamethasone. Other steroid analogs were also effective and their potencies paralleled their relative effectiveness as glucocorticoids. Analyses of competitive binding experiments conducted at 4 degrees C to minimize hormone internalization and degradation revealed the presence of a single class of CCK binding sites with a Kd of approximately 6 nM and indicated that dexamethasone treatment nearly tripled the number of CCK receptors/cell with little change in receptor affinity. Treatment with 10 nM dexamethasone increased both basal amylase secretion and the amylase released in response to CCK stimulation. In addition, dexamethasone increased the sensitivity of the cells to CCK. The glucocorticoid decreased the concentration of CCK required for one half-maximal stimulation of amylase secretion from 35 +/- 6 to 8 +/- 1 pM. These data indicate, therefore, that glucocorticoids induce an increase in the number of CCK receptors in AR42J cells, and this increase leads to enhanced sensitivity to CCK.

Irreversible inhibition by acetaldehyde of cholecystokinin-induced amylase secretion from isolated rat pancreatic acini

Acetaldehyde inhibited both amylase secretion induced by maximal concentrations (300 pM) of cholecystokinin octapeptide and the binding of radioiodinated cholecystokinin to receptors on isolated rat pancreatic acini. This inhibition was concentration dependent (10 mM to 1M for amylase secretion and 100 mM to 1M for binding). However, a correlation between the two inhibitory effects could not be obtained. Furthermore, the inhibitory effects were not reversible. Acetaldehyde did not alter the basal amylase secretion between 6 and 45 mM concentrations. However, 60, 100 and 300 mM acetaldehyde significantly decreased basal amylase secretion; no significant change in amylase secretion was observed at 600 mM and 1M. Higher concentrations of acetaldehyde produced a 2- to 10-fold increase in basal amylase secretion. 51Cr release from prelabeled acini revealed no significant cell membrane damage between 10 and 600 mM acetaldehyde. These data suggest that acetaldehyde inhibition of cholecystokinin-induced amylase secretion is intracellularly mediated.

PIRENZEPINE: A RELATIVELY WEAK ANTAGONIST OF MUSCARINIC RECEPTOR IN ISOLATED MOUSE PANCREATIC ACINI

The effects of pirenzepine, a selective antimuscarinic agent, on both carbachol-stimulated amylase release and [3H]N-methyl scopolamine ([3H]NMS) binding were studied in isolated mouse pancreatic acini. Pirenzepine at concentrations between 0.1-3.0 μM was found to inhibit carbachol-stimulated amylase release without any appreciable effect on the basal amylase secretion. The inhibition by pirenzepine was rapid and reversible. Biphasic dose-response curves to carbachol for amylase release shifted to the right with an increase in pirenzepine concentration, and pA2 value was estimated to be 6.8. IC50 of pirenzepine for carbachol-stimulated amylase release was 440 nM, and the potency of pirenzepine on the inhibition of amylase release was 2% relative to atropine. The effect of pirenzepine was selective for carbachol; amylase release stimulated by other secretagogues such as cholecystokinin (CCK), bombesin and Ca2+ ionophore A23187, was not affected by pirenzepine. In addition, pirenzepine was found to inhibit the specific binding of [3H]NMS, a muscarinic antagonist, to mouse pancreatic acini. The potency of pirenzepine in this action was 1% relative to atropine. The inhibitory effect of pirenzepine on receptor binding was selective for the muscarinic receptor. These results indicate that pirenzepine is a specific but relatively weak antagonist of muscarinic receptor in mouse pancreatic acini.

Chronic administration of an organophosphorus insecticide to rats alters cholinergic muscarinic receptors in the pancreas

Male rats were treated for 10 days with the organophosphorus insecticide, acetylcholinesterase inhibitor, O, O-diethyl S-[2-(ethylthio)ethyl]phosphorodithioate (disulfoton, 2 mg/kg/day by gavage). At the end of the treatment, binding of [ 3H]quinuclidinyl benzilate ([ 3H]QNB) to cholinergic muscarinic receptors and cholinesterase (ChE) activity were assayed in the pancreas. Functional activity of pancreatic muscarinic receptor was investigated by determining carbachol-stimulated secretion of α-amylase in vitro. ChE activity and [ 3H]QNB binding were significantly decreased in the pancreas from disulfoton-treated rats. The alteration of [ 3H]QNB binding was due to a decrease in muscarinic receptor density with no change in the affinity. Basal secretion of amylase from pancreas in vitro was not altered, but carbachol-stimulated secretion was decreased. The effect appeared to be specific since pancreozymin was able to induce the same amylase release from pancreases of control and treated rats. The results suggest that repeated exposures to sublethal doses of an organophosphorus insecticide lead to a biochemical and functional alteration of cholinergic muscarinic receptors in the pancreas.