Structural and functional changes of rat exocrine pancreas exposed to nicotine

Nicotine, an addictive agent in cigarette smoking, has been implicated in the etiology of pancreatitis and pancreatic carcinoma. Very little experimental data are, however, available regarding the effects of nicotine on the structural and functional changes in the exocrine pancreas. Two groups of rats divided into control and nicotine exposed were used. The animals in the nicotine group were maintained for 28 d with ad libitum water containing 0.77 mM of nicotine. At term, the animals were sacrificed, and pancreas was examined for pathological and functional changes. Nicotine induced cytoplasmic vacuolation and cellular edema in the exocrine pancreas. Plasma levels of glucose and insulin and CCK-8-stimulated amylase release in isolated acini were significantly decreased by nicotine, whereas the total cellular amylase content was significantly increased. Analysis of competitive ligand binding data on membranes from isolated acini showed that the Bmax and Kd values for CCK receptors were not significantly changed by nicotine, p > 0.05. These data indicate that a postreceptor mechanism is involved in the inhibition in stimulus-secretion coupling of enzyme secretion by nicotine. The increase in total cellular amylase content and decreased enzyme secretion by nicotine may be implicated in the induction of pancreatic pathology.

Effects of diet on cholecystokinin-stimulated amylase secretion by pancreatic Acini and amylase mRNA levels in rat pancreas

To investigate the mechanisms by which dietary compositions regulate the exocrine pancreas, we examined the effects of no-fat diet (NFD) and high-fat diet (HFD) on cholecystokinin (CCK)-stimulated amylase secretion from rat pancreatic acini. Rats were maintained for 4 weeks on NFD or HFD, which contained 0 or 45% fat and 58 or 29% carbohydrates, respectively. Pancreatic acini were isolated and stimulated by graded doses of CCK for 30 min. Maximal CCK-stimulated amylase secretion by pancreatic acini from rats on NFD (23.1 +/- 4.3 U/mg protein at 10(-10) M) was significantly higher than that of HFD (5.5 +/- 1.6 U/mg protein at 10(-10) M). In contrast, expressed as a percentage of the initial content, maximal CCK-stimulated amylase secretion by pancreatic acini from rats on NFD (15.0 +/- 0.8%) tended to be lower than that from rats on HFD (28.1 +/- 3.5%). To study further the effects of the diets on amylase mRNA levels, another group of rats was maintained on the respective diets for 4 weeks, sacrificed, and total pancreatic RNA isolated. Amylase mRNA levels in rats on NFD were 2.5 times higher than in rats on HFD. The results suggest that alterations in CCK-stimulated amylase secretion by pancreatic acini, as well as modifications in pancreatic amylase expression, may be involved in the mechanisms by which the exocrine pancreas adapts to diet.

Vanadium: a modifier of drug-metabolizing enzyme patterns and its critical role in cellular proliferation in transplantable murine lymphoma

Vanadium, as ammonium monovanadate, has been found to stimulate tumour cell proliferation in mice bearing a transplantable ascitic lymphoma. Markers including microsomal cytochrome P-450, UDP-glucuronyltransferase and cytosolic glutathione-S-transferase showed substantial alterations in a dose-responsive manner with vanadium administration when compared to the controls. Stimulation of tumour progression is also reflected by increased tumour cell count and decreased survival of the host.

Carbachol and cholecystokinin enhance accumulation of nicotine in rat pancreatic acinar cells

Nicotine is a possible risk factor for chronic pancreatitis and pancreatic cancer. To study the loci where nicotine might exert its effect, we examined interactions between nicotine and rat pancreatic acini. When pancreatic acini were incubated with [3H]nicotine, [3H]nicotine levels in pancreatic acini were increased in time-and dose-dependent manners, and the t1/2 for dissociation of [3H]nicotine was 63.8 min. At 4 degrees C, the association of [3H]nicotine was 33% of the association at 37 degrees C. Unlabeled nicotine had no significant effect on the accumulation of [3H]nicotine. In addition, surface-bound [3H]nicotine was not detected when acini were washed in a low-pH solution or when they were trypsinized. These results suggest that the accumulation of nicotine may be a biological phenomenon and that [3H]nicotine does not bind to surface receptors of acinar cells, but accumulates intracellularly. The addition of verapamil (0.1 mM) or 12-O-tetradecanoylphorbol-13-acetate (1 microM) had no effect on [3H]nicotine association, while 4-bromo-A23187 (2 microM) or EGTA (10 mM) significantly increased the accumulation of [3H]nicotine. Carbachol and cholecystokinin significantly enhanced the accumulation of [3H]nicotine in a dose-dependent manner. Taken together, the increasing effects of carbachol and cholecystokinin on the accumulation of nicotine may explain, at least in part, the mechanisms involved in the multiplicative effects of the combination of two risk factors, smoking habit and high-fat or high-protein diets, on human pancreatic diseases.

The influence of vagotomy on basal and postprandial pancreatic secretion and plasma levels of gastrointestinal hormones in conscious rats

This study was conducted to investigate the effect of vagotomy on basal and postprandial pancreatic secretion and plasma levels of gastrointestinal hormones. Thirteen rats underwent vagotomy and 12 underwent sham operation. All of the rats were prepared with gastric and pancreatic fistulas. Before and after an intragastric infusion of liquid meal, pancreatic fluid and protein outputs and plasma levels of cholecystokinin and gastrin were measured. Vagotomy induced a delay and a decrease in postprandial responses in pancreatic volume and protein outputs. Vagotomy had no effect on basal and postprandial plasma levels of cholecystokinin. Basal and postprandial levels of plasma gastrin were significantly increased after vagotomy, but the postprandial patterns of gastrin release were not significantly different between the two groups. Vagal regulation may be important in the basal gastrin release but is not involved in basal release of cholecystokinin or postprandial releases of gastrin and cholecystokinin. The current results indicate that vagotomy influences postprandial pancreatic secretion. This effect is probably the result of interrupted vagus-mediated reflexes between the intestinal tract and the pancreas.

The role of gastrointestinal peptides on pancreatic secretion in response to different stimulants in conscious rats

Effects of intragastric food, intraduodenal amino acids, and intravenously administered bombesin and gastrin-releasing peptide (GRP) were examined in conscious rats with pancreatic fistula in terms of responses of exocrine pancreatic secretion, plasma levels gastrin, and cholecystokinin (CCK). Pancreatic juice and blood samples were collected at regular intervals before and after the stimuli. Intragastric food increased pancreatic secretion and plasma levels of gastrin and CCK. Intraduodenal infusion of amino acids had no effect on pancreatic secretion and plasma levels of gastrin and CCK. Intravenous infusion of bombesin at 1 microgram/kg/h induced significant increases in pancreatic volume and protein outputs, but had no effect on plasma levels of gastrin and CCK. Bombesin infusion at 10 micrograms/kg/h resulted in significant increases in pancreatic volume and protein outputs as well as plasma gastrin levels, but had no effect on plasma CCK levels. Intravenous infusion of GRP induced increases in pancreatic volume and protein outputs and plasma gastrin levels, but had no effect on CCK levels. Antrectomy resulted in significant decreases in basal levels of plasma gastrin. GRP-stimulated pancreatic volume and protein outputs were not significantly changed by antrectomy. In rats that underwent antrectomy, GRP infusion significantly increased pancreatic volume and protein outputs, but had no effect on plasma levels of gastrin and CCK. Food-stimulated pancreatic secretion and plasma levels of gastrointestinal peptides of rats were similar to other species, but amino acids, bombesin, or GRP may not be the stimulants for CCK release in rats. The stimuli that release CCK from duodenal mucosa probably varies among species.

Agonist-regulated alteration of the affinity of pancreatic muscarinic cholinergic receptors

Heterologous desensitization is a term that indicates that exposure of a cell to an agonist attenuates the response of that cell to other agonists. We examined heterologous desensitization of muscarinic cholinergic receptors of pancreatic acini and characterized mechanisms that might be responsible for desensitization. Muscarinic cholinergic receptor binding was measured by using N-[3H]methscopolamine bromide ([3H]NMS). N-Methscopolamine bromide (NMS), a receptor antagonist, bound to a single class of receptors with an affinity of 0.22 +/- 0.04 nM and a capacity of 61.5 +/- 5.1 fmol/mg of protein. These parameters of NMS binding sites were not altered by an addition of cholecystokinin (CCK) octapeptide, CCK-JMV-180, vasoactive intestinal peptide, 8-bromo-cAMP, 4-bromo-A23187, thapsigargin, or 12-O-tetradecanoylphorbol-13-acetate (TPA). Analysis of competitive inhibition curve of [3H] NMS binding by carbachol showed apparently two classes of carbachol binding sites with high affinity (38.6%) and low affinity (61.4%). Simultaneous incubation of carbachol with CCK or TPA increased the relative affinity of [3H]NMS binding, and the competitive inhibition curves showed a single class of carbachol binding site. L-364,718 blocked the effect of CCK, and staurosporine blocked the effects of TPA and partially blocked the effect of CCK. CCK-JMV-180, vasoactive intestinal peptide, 8-bromo-cAMP, 4-bromo-A23187, and thapsigargin had no effects on the competitive binding. Second, the carbachol-induced sequestration of the receptors was examined. Incubation of acini with carbachol resulted in a decrease of [3H] NMS binding sites, and the addition of CCK or TPA caused an inhibition of the carbachol-induced disappearance of [3H]NMS binding sites. Finally, studies that examined the biological response of the acinar cells showed that biphasic amylase release in response to carbachol was completely suppressed by 10 nM CCK for entire range of carbachol. Taken together, these results suggest that the effect of CCK on carbachol-induced sequestration is important for the alteration of the apparent affinity of carbachol binding sites and the biological response of acinar cells to carbachol. Further, the results suggest that another factor that induces uncoupling of receptor from effector might be involved in agonist-regulated desensitization. The results, that CCK-JMV-180 or other agonists that activate the adenylate cyclase pathway did not exert these effects of CCK, suggest that protein kinase C may be one of the key factors involved in heterologous desensitization by CCK on the carbachol binding sites and the suppression of carbachol-induced amylase release.

The effect of intravenous cadmium on exocrine and endocrine pancreatic functions in conscious dogs

This study was conducted in conscious dogs to investigate the effect of cadmium on exocrine pancreatic secretion and plasma levels of pancreatic polypeptide (PP). Mongrel dogs weighing 20-25 kg were prepared with chronic gastric and pancreatic fistulas, and were acclimated for 3 wk prior to studies. The dogs were given iv infusion of saline, secretin at 25 U/kg/h, cadmium at 0.15 mg/kg/h, or various combinations of these compounds. During the infusion, pancreatic juice and blood samples were collected at regular intervals. Secretin infusion stimulated pancreatic secretions. Infusion of cadmium alone had no effect on pancreatic secretions and plasma levels of PP. When cadmium infusion was stopped with the background infusion of secretin, pancreatic secretions and plasma levels of PP were significantly increased. This latent effect of cadmium on pancreatic secretions and plasma levels of PP was abolished by an iv injection of 100 mg/kg atropine. These results indicate that cholinergic signaling may be involved in the effect of cadmium on pancreatic exocrine secretions and PP release. The current study suggests that cadmium may have diverse physiological functions in both exocrine and endocrine pancreatic cells.

Retrieval and amplification of DNA from unstained histopathological sections

Testing of compounds for carcinogenic potential in vivo involves various experimental designs. A few of these techniques are directed to demonstrate the genotoxicity and mutagenicity of the compound by histopathology. These changes shown by histochemical means include monoclonal antibody directed cellular markers. Development of the polymerase chain reaction technique (PCR) for amplification of DNA has facilitated the investigation of molecular events related to the formation of malignant neoplasms. We describe here a method for screening tissues for mutations of the H-ras gene using monoclonal antibodies directed toward normal and mutant p21 proteins. Formalin-fixed, paraffin-embedded tissue sections are used to subsequently confirm the gene mutation by PCR amplification of the H-ras gene. The results indicated a successful application of this technique to demonstrate the presence of p21 oncoprotein in the tissues tested.

Exogenous administration of estradiol and cholecystokinin alters exocrine pancreatic function in rats

This study was conducted in rats to investigate the influence of exogenously administered estradiol (ESD) and/or cholecystokinin (CCK) on components and secretions of the pancreatic acini. Intact male rats were treated for 14 d with exogenous administration of ESD, CCK, or ESD+CCK. After 14 d CCK treatment induced significant increases in DNA and RNA contents, and DNA/RNA ratio in the pancreas, indicating hyperplasia and hypertrophy of the pancreas, however, ESD treatment did not have these effects. Both ESD treatment and CCK treatment induced significant increases in amylase and trypsinogen contents in pancreatic acini and each decreased secretion from acini in response to CCK. Combined treatment with ESD plus CCK augmented these effects on enzyme contents and secretion. The results indicate that exogenous administration of CCK has trophic effects on the exocrine pancreas, increasing effects on enzyme contents and inhibitory effects on amylase secretion. In contrast, exogenous administration of ESD had no trophic effects on pancreas, but had increasing effects on enzyme contents and inhibitory effects on amylase secretion. The results suggest that the effects of exogenous ESD and CCK on pancreas are not similar to each other, but both ESD and CCK may be involved in regulating pancreatic exocrine functions.