Influence of pancreatic ducts on saturation of juice with calcium carbonate in dogs.

In several species, bicarbonate and calcium concentrations of pancreatic juice are known to vary during the different phases of pancreatic secretion. The effects of these variations on the saturation of juice with calcium carbonate, a critical factor for the formation of pancreatic stones, are not known. In this work, we studied the saturation degree of pancreatic juice with calcium carbonate in six unanesthetized beagle dogs equipped with Thomas cannulae during basal secretion and after bolus injections of cerulein (30 ng/kg) or secretin (0.25 units/kg). In the different samples of pure pancreatic juice, pH, PCO2, bicarbonate, and proteins were measured by standard methods. Total calcium (CaT) and ionized calcium (Ca2+) were determined using calcium-specific electrodes. Saturation with calcium carbonate was calculated by reference to the solubility product of calcite at 37 degrees C. Almost all the samples were found to be supersaturated with calcium carbonate but large variations of the saturation index were observed. In basal samples, obtained during periods of low secretion rate, the mean saturation index (3.35 +/- 3.01) was significantly lower than under secretion (12.10 +/- 5.14) or cerulein (18.01 +/- 8.42). This low basal saturation index, in spite of a high Ca2+ content, was explained by a low bicarbonate concentration (37.6 +/- 18.9 mmol/liter) and a high PCO2 (13.4 +/- 7.5 kPa). In contrast, in juice obtained after hormonal stimulation, PCO2 (4.8 +/- 1.6 kPa) was similar to plasma PCO2 (5.5 +/- 1.2 kPa).(ABSTRACT TRUNCATED AT 250 WORDS)

Dog gastric lipase: stimulation of its secretion in vivo and cytolocalization in mucous pit cells.

Dog gastric lipase (DGL) secretion is stimulated in vivo by urecholine, pentagastrin, histamine, 16,16-dimethyl prostaglandin E2, and secretin. Under fasting conditions, DGL is irreversibly inactivated by gastric acid below pH 1.5; consequently, DGL output can be underestimated. This problem has been resolved by buffering the acid or by using an antisecretory drug such as omeprazole during stimulation. There is a clear parallelism between the secretion of DGL and of gastric mucus. This observation led to the present investigation of the cellular localization of DGL using immunofluorescence techniques. Results showed that DGL is cytolocalized in mucous pit cells of gastric glands. Pepsinogen is found in chief cells. To the authors' knowledge, this is the first description of an enzyme (gastric lipase) secreted by mucous-type gastric cells. In contrast to other species, gastric lipase of the dog is located in cardiac, fundic, and antral mucosae.

The cephalogastric phase of the pancreatic response to food in the dog.

We studied post-meal pancreatic secretion and gastrin release in conscious dogs with duodenal Thomas cannulas. Normal dogs were tested in physiological conditions and with an i.v. infusion of atropine 20 micrograms/kg/h or secretin 0.5 CU/kg/h. The responses were also studied after antral and truncal vagotomy. In the early phase (0-20 min) of the response, before gastric emptying started, antral vagotomy reduced fluid and protein outputs, and truncal vagotomy reduced them still more. Atropine reduced only the protein response. Gastrin release reached a peak after 20-25 min. After antral and truncal vagotomy, gastrin release was reduced within 10 min after the meal. Late-phase (greater than 20 min) pancreatic secretion depended on the presence of chyme in the duodenum. The effects of atropine and antral vagotomy in the cephalogastric phase could be explained by antropancreatic reflexes stimulating fluid secretion (atropine-resistant pathway) and protein output (atropine-sensitive pathway).

Structural and functional effects of long-term alcohol administration on the dog exocrine pancreas submitted to two different diets.

Our purpose was to study the influence of two different levels of dietary protein and fat on the action of chronic alcohol feeding on the exocrine pancreatic secretion and the pancreatic morphology of conscious dogs. Ten animals were provided with gastric and duodenal cannulas. Five of them (group H) received a high-protein (39% of calories), high-fat (34%) diet, and the five others (group L) a moderately low-protein (15%), low-fat (20%) diet. Animals were housed in closed kennels lightened with artificial light and did not have free access to sunlight. Five series of experiments were performed just before and 5 and 12 months after daily alcohol administration through the gastric cannula (2 g/kg/day). Volume, bicarbonate, and protein were measured under basal conditions after intragastric ethanol infusion (1.5 g/kg), under hormonal stimulation with 1 clinical unit (CU)/kg/h secretin or 1 CU/kg/h secretin plus 3 Crick Harper Rate (CHR) U/kg/h cholecystokinin (CCK), before and after intravenous ethanol 1.3 g/kg for 20 min, and after intragastric ethanol (1 g/kg) given with a meal. Group H was the most sensitive to the action of chronic alcohol feeding. At the end of 1 year of alcohol administration, volume and bicarbonate were not affected, but protein secretion was significantly increased in basal conditions and under secretin infusion, but not under CCK infusion or in response to a meal. The secretory pattern of these dogs was different from the response of dogs studied in previous experiments having the same diet but housed in an open kennel and having free access to outside and sunlight. In group L, protein was less affected, but volume and bicarbonate were significantly decreased 1 year under secretin stimulation. Histological damages were seen in the two groups characterized by a slight periacinar fibrosis and alterations of ductal cells. Acinar and ductal luminae were dilated and filled with protein plugs also present in pancreatic juice and able to stop the flow of juice. At the difference from human beings, these plugs were built up of all secretory protein but not of an insoluble fibrillar molecular form of pancreatic stone protein. This study confirms the role of chronic alcoholism on the formation of protein plugs and shows the influence of nutritional and environmental conditions.

Pancreatic exocrine responses to secretin, 2-deoxyglucose, a meal, and ethanol after coeliac ganglionectomy in the conscious dog.

The effects of coeliac ganglionectomy on pancreatic exocrine responses to graded doses of secretin, intravenous 2-deoxyglucose 100 mg/kg, ethanol 0.56 g/kg, and 1 g/kg, and to a meat meal were studied in conscious dogs (weight 11 to 27 kg). Five animals underwent coeliac ganglionectomy and up to seven control animals were studied. Coeliac ganglionectomy increased four-fold the pancreatic fluid response to secretin. The early part of the fluid response to 2-deoxyglucose was reduced, but there was no effect on the protein response to 2-deoxyglucose. In controls, ethanol 0.56 g/kg stimulated pancreatic secretion, to nearly double the basal level, but after coeliac ganglionectomy this dose of ethanol inhibited secretion to one third of basal values. There was no effect of coeliac ganglionectomy on pancreatic response to ethanol 1 g/kg. After coeliac ganglionectomy the early response to a meal was increased by 100% for fluid output and by 50% for protein secretion, but from 10 minutes to two hours after the meal there was no effect on pancreatic response. These data shed further light on the mode of action of ethanol on pancreatic secretion, and they indicate that therapeutic coeliac ganglia ablation in man is unlikely to be detrimental to physiological pancreatic secretion.

The effect of oxyntomodulin (glucagon-37) and glucagon on exocrine pancreatic secretion in the conscious rat.

The inhibitory effect of glucagon on exocrine pancreas has been the subject of controversial reports. On the other hand, oxyntomodulin (bioactive enteroglucagon or glucagon-37), a 37 amino acid peptide isolated from porcine lower intestine, has been shown to be 10-20 times more potent than glucagon in inhibiting gastric acid secretion in the rat. In view of this, the effect of glucagon and oxyntomodulin on basal and caerulein-stimulated pancreatic secretion has been studied, during re-introduction of pancreatic juice into duodenum, in the conscious rat provided with pancreatic and duodenal fistulas. A depression of pancreatic function was observed with both peptides on the three parameters studied: (volume of juice secreted, bicarbonate and protein output), either under basal conditions or during stimulation by caerulein. In all the experimental conditions used, oxyntomodulin was ca. ten times more potent than glucagon in its inhibitory effect. The fact that oxyntomodulin, as what is observed in the stomach, is one order of magnitude more potent than glucagon in inhibiting pancreatic secretion suggests that the biological mechanisms by which the peptides of the glucagon-family act on exocrine pancreas are similar, or related to that present at the gastric level.

Pancreatic responses to endogenous and exogenous gastrin in the dog.

Serum gastrin and pancreatic secretion were measured in conscious Thomas fistula dogs during infusion of increasing doses of porcine gastrin, against a background of secretin. Dose-response relationships were calculated for the effects of gastrin on pancreatic secretion. Gastrin release was also measured after a test meal and after vagal stimulation with 2-deoxyglucose. Peak serum gastrin levels after these stimuli were less than the serum gastrin level associated with the minimal effective dose of gastrin. From the dose-response relationship of serum gastrin and pancreatic protein output, it was possible to calculate the protein output corresponding to the peak gastrin levels after 2-deoxyglucose or a meal. These were equivalent to 20-30% of the observed protein response to these stimuli. We conclude that gastrin plays at most a small part in the stimulation of pancreatic secretion after a meal and in response to 2-deoxyglucose. We also found that truncal vagotomy reduces pancreatic sensitivity to gastrin.

Neural pathways for the release of gastrin, cholecystokinin, and pancreatic polypeptide after a meal in dogs. Role of gastric and splanchnic nerves.

We have measured gastrin, cholecystokinin (CCK), and pancreatic polypeptide (PP) release after a meal in normal dogs under basal conditions and during atropine infusion, and after various neural sections. Denervation of the gastric antrum (antral vagotomy) abolished the early part of the gastrin response to food. Truncal vagotomy, celiac ganglionectomy, and atropine reduced the early release of CCK, which occurred before the start of gastric emptying, suggesting that a neural, cholinergic mechanism may release CCK immediately after a meal. PP release was abolished by truncal vagotomy, and also by antral vagotomy. As no direct pathways are known between the antrum and the pancreas, this suggests either that antral afferents are essential for this response or that vagally mediated hormone release from the antrum mediates PP release.

Action of dopamine on the exocrine pancreatic secretion of the intact dog.

The effects of dopamine and domperidone, a dopamine antagonist, have been studied on the exocrine secretion of the dog pancreas. The purpose of this study was to see if dopamine acted on enzyme secretion and if its action was merely 'pharmacological' or had a physiological role. Conscious Beagle dogs, fitted with Thomas cannulae were studied following infusions of dopamine 125-1000 micrograms kg-1 h-1. During dopamine infusion, a secretory peak lasting 10 min was observed. This was followed by a stable plateau which was approximately 1/3 of the peak. The pattern of water, bicarbonate and protein secretion was similar. The maximum effect was obtained with 500 micrograms kg-1 h-1 dopamine. The stimulatory action of dopamine was blocked by domperidone, without any detected effect on the central nervous system, but not by propranolol or phenoxybenzamine. Domperidone 10 micrograms kg-1 almost completely suppressed the secretory response to the maximally effective dose of dopamine. This inhibition was not competitive. Atropine decreased the secretory response to dopamine. The protein response was not observed when dopamine was infused against a background infusion of secretin. This suggests that the effect of dopamine on protein secretion could be due to a wash-out phenomenon. The maximally effective dose of domperidone, 10 micrograms kg-1, did not modify the pancreatic response to a solid meal. Thus, in the non-anaesthetized dog, the effect of dopamine on water and bicarbonate secretion has been confirmed. It is concluded that dopamine had no detectable action on protein secretion and that the physiological role of dopamine with respect to pancreatic secretion is still questionable.

Entero-pancreatic reflexes revealed by duodenal anesthesia in the dog.

This study was designed to improve our understanding of duodeno-pancreatic reflexes, the existence of which was suggested by the previous observation of a reduction in secretin-stimulated pancreatic secretion during local anesthesia of the duodenal mucosa. The effects on this reduction in secretin-stimulated secretion of cholinergic or adrenergic blocking agents (alone or in combination) and of truncal vagotomy, were studied in conscious dog with gastric and pancreatic fistulae. For each agent and for secretin alone in normal and vagotomized dogs, a comparison was made of pancreatic secretion with and without lignocaine anesthesia of the duodenal mucosa. Lignocaine reduced pancreatic secretion with secretin alone, and stimulated it during infusion of atropine. The changes in both protein bicarbonate secretion were blocked by pentolinium and by phenoxybenzamine whereas propranolol mainly blocked the effects on bicarbonate output. The effect of truncal vagotomy resembled that of atropine. These results suggest the existence of two enteropancreatic reflex mechanisms; an excitory cholinergic vagal reflex and an inhibitory, atropine-resistant non-vagal reflex. Both are blocked by pentolinium (a ganglion blocker) and by phenoxy-benzamine, suggesting the involvement of alpha-adrenergic receptors probably also at the level of the ganglion cell. Beta-adrenergic receptors are also involved in the regulation of bicarbonate and fluid secretion.

Effect of acute and chronic oral administration of ethanol on canine exocrine pancreatic secretion.

The action of an intragastric injection of ethanol (1.0-1.5 g/kg), either in the fasting animal or with a solid meal, has been studied in two groups of 4 conscious dogs provided with gastric and duodenal Thomas cannulae: one group of 'alcoholic dogs' (AD) had been given 2 g/kg/day ethanol over a period of 24 months, the second group of 'nonalcoholic dogs' (NA) had been given water as control. In NA, intragastric ethanol inhibited water and bicarbonate secretions, alcohol being given in the fasting animal or with a meal. In AD: (a) the nonstimulated output of water and bicarbonate, and to a lesser extent of protein, was decreased compared to NA, protein concentration being increased; (b) the bicarbonate response to a meal without ethanol was decreased, and (c) the most interesting finding is that in AD, the inhibitory action of intragastric ethanol as observed in NA, disappeared and was even replaced by a stimulation of water, bicarbonate and protein secretions. The disappearance in AD of alcohol-induced mechanisms inhibiting pancreatic secretion had already been found with other experimental protocols and involves muscarinic receptors. Inhibition of water and bicarbonate secretions remains unexplained.

Vagal influence on exocrine pancreas of alcohol-fed and of normal dogs.

A histochemical study has indicated increased activity of acetylcholine in the pancreas of chronic alcoholic dogs, and we have recently reported decrease pancreatic responsiveness to cholinergic stimulation in such dogs. This prompted us to determine, in chronic alcoholic dogs, the net pancreatic response to stimulation mediated by cholinergic nerves. Therefore, the pancreatic response to vagal stimulation by intravenous 2-deoxy-d-glucose (2DG) infusion was examined in such dogs and in controls. After 2DG, 100 mg kg-1, significant and similar increases in protein output up to maximally 2.7 +/- 0.8 and 2.3 +/- 0.5 mg kg-1 (15 min)-1 were observed in control and alcohol-treated dogs. A significant rise in flow rate and HCO-3 output up to maximally 0.26 +/- 0.07 ml kg-1 (15 min)-1 and 43 +/- 13 mumol kg-1 (15 min)-1, respectively, occurred in the controls but was delayed in the alcoholics. The finding in alcoholic dogs of no change in protein response to 2DG is not in favour of a primary increase of vagally mediated pancreatic protein secretion. It could, however, be compatible with a primary increase in cholinergic receptor resistance due to alcohol and secondary adaptive increase in cholinergic activities, which when combined, would yield no net change of the cholinergically mediated protein response.

Influence of environmental conditions on exocrine pancreatic response to intravenous injection of ethanol or 2-deoxyglucose in the dog.

When dogs have free access to the outside, an intravenous injection of ethanol depresses secretin-stimulated exocrine pancreatic secretion by a vagally mediated mechanism. This was shown in two separate series of six and seven dogs each. When dogs were kept in air-conditioned windowless kennels, the response to a meal was unchanged but the response to ethanol was reversed to stimulation. In four dogs, ethanol 1 g/kg was given during a secretin infusion. Three months after changing from open to closed kennels the inhibition (-86% for protein output) was still present, but after 6 months ethanol produced a stimulation (+62%) of pancreatic secretion. This increase was abolished, but not reversed, by keeping the animals outside during the day for four weeks, whereas after three months there was a partial restoration of the inhibitory effect (-39%). In contrast, changing from an open to a closed kennel changed the initial response to 2-deoxy-D-glucose (2-DG), 100 mg/kg, from stimulation to inhibition. These results suggest that environmental conditions affect the cranial regulation of pancreatic secretion.

Cholinergic stimulation and inhibition of pancreatic secretion in alcohol-adapted dogs.

There is indirect evidence of increased release of acetylcholine in the exocrine pancreas of chronically alcoholic dogs. Our aim was to ascertain whether altered pancreatic responsiveness to cholinergic stimulation was an associated phenomenon. Pancreatic dose-response tests with graded bethanechol stimulation on constant secretion stimulation, without or with a low dose of background atropine, were performed in four chronic gastric and duodenal fistula dogs after 3 and 12 months of intragastric feeding with ethanol. The secretory protein response was dose-dependently increased by bethanechol in the control dogs but not in the test dogs, after 3 or 12 months of daily alcohol. They responded significantly only to a dose four to eight times greater than the minimum effective dose in the control dogs. Atropine depressed the entire dose-response curve of these dogs but only the response to the greatest doses in the alcohol-treated dogs. In previous experiments caerulein and/or secretin evoked increased secretory responses of bicarbonate in chronically alcoholic dogs, but this was not the case in this study with bethanechol, which did not have a stimulating effect on bicarbonate in either test or control dogs. Concomitant atropine, however, unmasked a bicarbonate-stimulating effect of bethanechol in control but not in treated dogs. It is concluded that chronic alcohol-feeding, already after 3 months, leads to a diminished pancreatic responsiveness to cholinergic stimulation and inhibition of protein output, as evidenced by at least a fourfold increase of the minimum effective dose of bethanechol and diminished inhibitory action of atropine.

The role of nicotinic receptors in dog pancreatic exocrine secretion.

1 The effects of pentamethonium, an autonomic ganglion blocker, were studied on the exocrine pancreatic secretion of six conscious dogs given intravenous infusions of urecholine, caerulein or pentagastrin on a background of submaximal doses of secretin. 2 Urecholine-induced protein secretion was not affected but both caerulein- and to a smaller extent, pentagastrin-induced protein secretions were depressed by pentamethonium. 3 These results indicate that intravenous caerulein and pentagastrin, but not urecholine, act at least partially via nicotinic receptors. 4 Volume and bicarbonate output were depressed by pentamethonium when stimulated by intravenous caerulein with a background of secretin, but not when stimulated by pentagastrin on a background of secretin. 5 From these data it is suggested that caerulein and pentagastrin may potentiate secretin-stimulated hydrelatic secretion by different mechanisms.

Repeated I. V. injections of calcium salts give rise to increased exocrine pancreatic cell sensitivity to caerulein and urecholine in the dog.

The persisting modifications induced by repeated intravenous infusion of calcium salts were investigated in five dogs with Thomas fistulae. Five control dogs were also tested. In calcium treated dogs the pancreatic secretion stimulated by graded doses of either caerulein or urecholine showed: a) an increase in the sensitivity of acinar cells to caerulein and urecholine and potentiation by caerulein of the water and bicarbonate response to secretin, in contrast to the decreased sensitivity to secretin alone reported previously. b) an inhibition of water and bicarbonate secretion with urecholine stimulation, c) an inhibition of calcium secretion which was significant with caerulein. These findings could explain the data previously observed on basal pancreatic secretion of calcium treated dogs such as protein hypersecretion with protein precipitates and reduced bicarbonate secretion which are similar to modifications observed in chronic alcoholic dogs and men. These results have a clinical relevance to the understanding of the pathology of chronic pancreatitis.

Physiological conditions for the study of basal and meal stimulated exocrine pancreatic secretion in the dog. Absence of feedback inhibition of basal secretion.

Pancreatic secretion has been studied in dogs in basal and postprandial conditions, as nearly physiological as possible. When pancreatic juice was excluded from the duodenum pancreatic secretion was not raised, compared with secretion during the return of juice to the duodenum. In fact, in seven mongrels, returning pancreatic juice led a transient rise in pancreatic secretion. This was not seen in five beagles. These results indicate that dogs do not manifest the feedback control of pancreatic secretion by pancreatic juice observed in other species. Pancreatic secretory activity was determined in 10 dogs after stimulation by food. The highest secretion rates occurred during the initial 60 min. The maximal secretion of protein occurred before the maximal secretion of fluid and bicarbonate. The effect of the meal diminished slowly during the subsequent minutes but did not reach basal levels after 2 h. In physiological conditions, maximal pancreatic secretion of fluid and bicarbonate was about one-fifth and of protein was almost one-seventh of the maximal secretory capacity obtained with secretin and cholecystokinin, respectively. Potential specific activity of trypsinogen was unchanged during the different experimental conditions. Trypsinogen output represented a constant average of 20% of protein output. The interindividual variability of pancreatic secretion rates was reduced when outputs were expressed per kilogram of body weight. In general, a significant positive correlation was found between body weight and the secretory outputs. No differences were observed in the response of mongrel and beagle dogs to a meal.

Disappearance of an inhibitory factor of exocrine pancreas secretion in chronic alcoholic dogs.

In non-alcoholic dogs the exocrine pancreatic response to caerulein, but not to urecholine or secretin alone, was increased by atropine. This indicated a pancreatic inhibition triggered by the caerulein stimulation and blocked by atropine. The present aim was to examine whether atropine had a similar action on the caerulein-stimulated pancreatic secretion in dogs submitted to long-term alcohol feeding. Alcohol-fed dogs showed an increased volume and bicarbonate response to submaximal caerulein but a non-modified protein response as compared with the responses before alcohol adaptation. The elevated water and bicarbonate responses were not further enhanced by atropine, which, in contrast, enhanced the responses of normal dogs to such an extent as to equalize their responses with those of the treated dogs. Atropine, 5 micrograms X kg-1 X h-1, enhanced similar protein responses to submaximal caerulein more in normal than in alcohol-fed dogs, but with an eightfold higher atropine dose no enhance was produced in dogs alcohol-fed for 36 months. This dose of atropine still evoked a small and similar enhancement in the normal and 9-month-treated dogs. The enhancing action of atropine on caerulein-stimulated secretion, present in normal dogs, hence diminishes and finally disappears as a result of chronic alcohol feeding.