Gastrin and Acid Studies in the Pouch Dog

Serum gastrin and pouch acid secretion were measured in dogs with either innervated (Pavlov) or denervated (Heidenhain) pouches in the basal state and following a meat meal or insulin hypoglycaemia. The gastrin response to meat was consistently greater than to insulin hypoglycaemia and pouch acid output followed the changes in serum gastrin in both groups. These studies confirm that gastrin is the secretagogue responsible for acid secretion from a denervated pouch. They also indicate that intact vagal innervation is essential for the optimal effect of gastrin on acid secretion to be observed.     

Studies in dogs on the biphasic nature of the gastric secretory response to hypoglycaemia and other stimuli with special reference to the role of the adrenals: 1 The pattern of the biphasic response and the relation to gastric innervation and to hypoglycaemia

The gastric secretory response of dogs with fundal pouches to insulin hypoglycaemia is biphasic in character, the two secretory peaks being separated by some hours. The first response depends on the intact innervation of the pouch and is attributed to direct vagal action on the parietal cell. Experiments have been made to test the hypothesis that the second peak is due to activation of a pituitary adrenal mechanism.

The second phasic response does not depend on the intact innervation of the pouch and does not coincide with the period of hypoglycaemia. No relationship has been established with the second phase and plasma cortisol levels nor is this peak abolished by bilateral adrenalectomy. The second acid secretory response, however, is only evident when acid secretion of the main stomach makes prolonged contact with the antral mucosa; it is abolished by antrectomy. The hypothesis is put forward that the pattern of response following insulin hypoglycaemia after the initial vagal response is attributable to an interaction of acid-inhibiting and acid-stimulating mechanisms of gastric acid secretion mediated through the gastric antrum.

     

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).     

Inhibition of insulin secretion by intracerebroventricular infusion of pancreatic polypeptide in conscious dogs

Previously, we demonstrated that peripheral infusion of pancreatic polypeptide (PP) inhibits insulin response to several stimuli through vagal innervation. Since PP is found not only in pancreas but also in brain or cerebrospinal fluid, we studied the effect of intracerebroventricular infusion of PP on insulin secretion before and after vagotomy in dogs. Mongrel dogs were settled with a chronic cannula allowing intraventricular infusions into the third (n = 4) or lateral (n = 4) cerebral ventricle. All the experiments were performed one week after the operation in a fully conscious, relaxed state. Porcine PP (pPP, 50 ng or 5 micrograms/dog in 100 microliter saline), which has the same primary structure with that of canine PP, or saline alone was infused into the cerebral ventricles for 5 minutes at the rate of 20 microliter/minutes. As stimuli of insulin secretion, modified sham feeding (MSF; sight and smell of food for 5 minutes), glucose injection (IV-Glucose; 0.5 g/kg/30 seconds, intravenously) and CCK-octapeptide infusion (IV-CCK-8; 0.07 micrograms/kg/5 minutes, intravenously) were applied immediately after (and in some experiments various intervals after) the end of pPP or saline infusion into the ventricles. Immunoreactive PP or insulin was measured by a specific radioimmunoassay. Administration of PP caused significant inhibition of insulin secretion by MSF, IV-Glucose and IV-CCK-8 without affecting basal insulin secretion. The observed effect of the peptide was most potent when infused into the third cerebral ventricle at a dose of 50 ng/dog and not in a dose-related fashion. The integrated insulin responses to MSF, IV-Glucose and IV-CCK-8 were 28, 58 and 30%, respectively, as those of controls. This effect was likely to be of central origin because an overflow of PP to the periphery could not be observed by PP radioimmunoassay. Prior transthoracic bilateral truncal vagotomy abolished the suppressive effect of PP on glucose- and CCK-8-induced insulin secretion. Furthermore, the time course study of CCK-8 suggested that PP could interact with the regions surrounding the third cerebral ventricle. These results suggest that PP affects the central nervous system to control pancreatic insulin secretion via the vagus nerve like other peptides/neuroregulators which modify physiological processes (e.g. insulin release, acid secretion, motility).     

Neural pathways for the release of gastrin,cholecystokinin, and pancreatic polypeptide after a meal in dogs

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.     

Impaired Pancreatic Innervation after Selective Gastric Vagotomy

The secretion of pancreatic polypeptide (PP) was studied in 38 duodenal ulcer patients before, 4 months after, and, in 25 patients, again 18 months after either selective gastric vagotomy or parietal cell vagotomy. Selective gastric vagotomy on average reduced the PP response to food measured 4 months after operation to 20% of the preoperative value. The prolonged PP response (30-120 min) increased to 50% from the 4th to the 18th postoperative month (p < 0.005). Parietal cell vagotomy did not significantly change the PP response to food, although in a few patients (3/15) the response was reduced to below one third of the preoperative value. The PP response to insulin hypoglycemia was measured after operation in 16 patients; those who had a reduced PP response to food demonstrated a response to hypoglycemia which was reduced to the same extent. It is concluded that PP secretion is generally unaffected by parietal cell vagotomy but is impaired after selective gastric vagotomy and that the prolonged PP response to food is partially regenerated after vagotomy. It is suggested that selective gastric vagotomy interferes with the vagal innervation of the PP-rich head of the pancreas.     

Parietal cell vagotomy in dogs. Influence on heidenhain pouch acid secretion, serum gastrin concentration, gastric emptying and motility.

No change was observed in fasting Heidenhain pouch (HP) acid secretion and fasting serum gastrin concentration following parietal cell vagotomy (PCV) in six dogs whereas significant increase in food-stimulated pouch secretion and serum gastrin concentration was observed. The increase in pouch secretion after PCV took place mainly in the first 2 h after meal. The maximum serum gastrin concentration was reached at 15 min after feeding before as well as after PCV. Maximum in HP secretion was reached later, at 120 min before and at 90 min after surgery. Gastric emptying studies, using a food-barium meal, showed a slight decrease in the emptying rate after PCV in two dogs, while it was unchanged in the others. Cineradiography showed an unaffected antral motility in all dogs after PCV.     

Effects of truncal vagotomy and antrectomy on bombesin-stimulated pancreatic secretion,release of gastrin,and pancreatic polypeptide in the anesthetized dog

The short-term effects of truncal vagotomy and antrectomy on bombesin-stimulated pancreatic secretion and release of gastrin and pancreatic polypeptide (PP) were studied in 18 anesthetized dogs. Together with an intravenous infusion of secretin (250 ng/kg/hr) bombesin (500 ng/kg/hr) was given before and after truncal vagotomy, antrectomy, and sham operation (N=6 dogs per group). Peak incremental pancreatic protein output in procedures (tachyphylaxis). Neither truncal vagotomy nor antrectomy significantly altered the pancreatic protein response to bombesin when compared with sham operation. Bombesin produced a mean 1-hr increase over basal of 196 pM for gastrin, which was abolished by antrectomy but not appreciably affected by truncal vagotomy and sham operation. The mean 1-hr increment (207 pM) for PP in response to bombesin was not changed by truncal vagotomy, antrectomy, and sham operation. This study shows in the anesthetized dog that exogenous bombesin stimulates release of PP as well as gastrin; that the release of gastrin by bombesin is not vagally dependent; that neither truncal vagotomy nor antrectomy alter the release of PP by bombesin; and that the action of bombesin on pancreatic protein secretion does not depend on release of gastrin or on intact vagal nerves.Parts of this paper have been presented at the 12th European Pancreatic Club Meeting, Copenhagen, Denmark, October 11–13, 1979, and at the 3rd International Symposium on Gastrointestinal Hormones, Cambridge, England, September 15–18, 1980.     

Parietal cell vagotomy in dogs. A comparative study of the effects on gastric secretion and antral muscle contraction.

The aim of this work was to further investigate whether it is possible, through parietal cell vagotomy (PCV), to obtain both a complete suppression of the gastric secretory response to vagal impulses and to retain a normal contractile response of the antral muscle. Acid and peptic secretions, the electrical activity and the force of circular antral contractions were simultaneously studied in dogs, before and after PCV, under 2-deoxy-D-glucose (2DG) and pentagastrin (PG) stimulation. After PCV, the response to 200 mg/kg 2DG was reduced by about 70% for acid and 80% for pepsin; the slopes of the dose-response curves were significantly reduced after PCV. The slope of the regression line pepsin/acid after 2DG was decreased following PCV. The mean acid response to PG was reduced about 50% after PCV. Plasma immunoreactive gastrin increased following 2DG, and the variations were identical before and after PCV. The gastric control electrical activity in basal conditions (fasted dogs) and following 2DG was similar before and after PCV. The antral contractile response to 2DG was reduced by about 40% after PCV. In conclusion, when PCV induced an 80% reduction in the gastric secretory response to maximal vagal stimulation by 2DG, the contractile antral response was not entirely normal. This effect might be due either to a partial antral denervation or to some intrinsic influence of the denervated gastric body upon the strength of antral contractions.     

Parietal cell structure and acid secretion in the vagally innervated stomach and the vagally denervated fundic pouch in cats.

In seven cats provided with gastric fistula (GF) of the main stomach and a denervated Heidenhain pouch (HP) the structure of the innervated and denervated mucosa was examined by light and electron microscopy. In four of these cats dose-response curves for acid output to pentagastrin were determined before and after vagal denervation of the fundic pouch. Vagal denervation reduced the acid response to pentagastrin by decreasing both the secretory capacity and the sensitivity of the oxyntic glands. Accordingly, in the same cat the parietal cells of the HP were less sensitive to pentagastrin than the cells of the innervated main stomach. Light and electron microscopic investigations revealed that the fundic mucosa was thinner, and the size and proportion of the parietal cells was smaller in the HP than in the GF. It is likely that the morphological changes in the pouch were caused by the vagal denervation rather than by the loss of mucosal contact with food. The secretory and morphological changes produced by the vagotomy are not necessarily related.     

Mechanism of gastric acid response to pylorus ligation: effects of nephrectomy

In the rat nephrectomy raises the serum gastrin concentration but makes the parietal cells refractory to gastrin. Pylorus ligation stimulates the gastric acid output by a long vago-vagal reflex in innervated animals and by an intramural reflex in chronically vagotomized animals. Nephrectomy reduced the acid response to pylorus ligation in vagally intact rats but enhanced it in vagotomized rats. The acid response to pylorus ligation in all the experimental groups was inhibited by a muscarinic blocker, atropine, and by an H2-antagonist, metiamide. The serum gastrin concentration was raised by nephrectomy and by vagal denervation. Histamine mobilization from gastric endocrine cells is reflected in the activity of gastric histidine decarboxylase. The enzyme activity in pylorus-ligated innervated rats was raised by pentagastrin, atropine, and metiamide. In nephrectomized rats the basal enzyme activity was high, and it was raised further, slightly but significantly, by pentagastrin. The basal enzyme activity in pylorus-ligated rats was also quite high after vagotomy, and it was raised further by pentagastrin. After vagotomy + nephrectomy the basal enzyme activity was very high; it was not raised further by pentagastrin. It appears that both vago-vagal and intramural reflexes involve a cholinergic and a histaminergic pathway, that gastrin is not important for the neurally mediated acid response elicited by pylorus ligation, and that the postulated histaminergic pathway does not involve histamine derived from the gastric endocrine-like cells.     

Pancreatic polypeptide response to insulin in duodenal ulcer. Different levels in accordance with ulcer activity and its response to treatment

Pancreatic polypeptide is said to be a marker of vagal tone in duodenal ulcer. To determine whether pancreatic polypeptide levels are related to the course of duodenal ulcer, we studied acid and pancreatic polypeptide responses to insulin in 80 patients with duodenal ulcer disease: 40 with unoperated duodenal ulcer and 40 with proximal vagotomy. Data were analysed in accordance with the presence of an ulcer (active disease) and, when present, in accordance with the ulcer healing on medical treatment (cimetidine, 1 g/day for 4 weeks). In both groups acid and pancreatic polypeptide responses to hypoglycaemia were slightly correlated (r = 0.38) (p less than 0.05). The basal pancreatic polypeptide level was higher in patients with active disease than in those with inactive disease, who had a basal level similar to that of normal subjects of the same age range. Like the insulin-stimulated acid secretion, the pancreatic polypeptide response to insulin hypoglycaemia was higher in patients with active disease than in those with inactive disease (p less than 0.05): 26.1 +/- 3.9 versus 20.1 +/- 4 nmol/l/120 min, respectively, in unoperated patients and 34.8 +/- 2.2 versus 24.3 +/- 2.5 nmol/l/120 min, respectively, after proximal vagotomy. In active disease the pancreatic polypeptide response to insulin hypoglycaemia was higher in subjects whose ulcer did not heal further after cimetidine therapy than in those whose ulcer did. These data suggest that the pancreatic polypeptide response to insulin is an indicator of duodenal ulcer activity and is related to the treatment efficacy. These relationships are partly mediated by increased vagal tone.     

Physiological stimulation of pepsin secretion. The role of vagal innervation

The studies were performed on eight double-pouch dogs with one vagally innervated Amdrup pouch (AP) and one denervated Heidenhain pouch (HP), allowing comparison of pepsin secretion from innervated and denervated mucosa at the same time in the same animal. Food stimulation was done with a mixture of liver, heart, and bonemeal in doses of 1.25, 2.5, 5, 10, and 20 g/kg body weight, plus maximal stimulation by repeated meals of 5 g/kg every 15 min up to 10 times. 'Non-active' secretion of pepsin was determined by instillation in the pouches of 0.1 M and 0.005 M HCl dissolved in 0.15 M NaCl. The pepsin secretion in the HP equalled the 'non-active' output for all doses of food. In the innervated pouch there was an immediate, very high pepsin output similar to the response that can be elicited by 2-deoxy-D-glucose and bethanechol chloride. The secretion of pepsin was gradually reduced, but it was, as long as the volume and electrolyte secretion lasted. well above the 'non-active' level. The results show that stimulation of pepsin secretion by food is completely dependent on intact vagal innervation. The volume and acid output were increased as the dose of food was increased, but the concentration of pepsin was stepwise reduced when the volume increased, resulting in approximately the same output of pepsin for all doses of food. The pepsin to acid ratio was statistically higher in juice secreted from innervated than from denervated mucosa for all doses of food, for lower doses of histamine and pentagastrin, and for higher doses of bethanechol chloride.     

Graded vagotomy and gastric secretion

In 3 dogs with gastric fistulae, partial denervation of the acid secreting area of the stomach halved the insulin-stimulated acid secretion. Completion of a “highly selective” (proximal gastric) vagotomy resulted in a further fall of the peak acid output after insulin to 4% of control values, and there was no further change when selective and truncal vagotomy were performed. The pentagastrin dose-response curve was shifted to the right after partial denervation and remained so shifted after subsequent operations. At low doses there was a considerable decrease in acid output, and the maximal acid output was unchanged but achieved only with a higher dose of pentagastrin. These results suggest that the gastric secretory response after vagotomy is not an all-or-none phenomenon and that the fall in peak acid output after insulin is related to the extent of the acid-secreting mucosa denervated. Tailored vagotomy operations might lower the acid secretion sufficiently to heal an ulcer without interfering with other aspects of gastrointestinal function.     

Is antral gastrin important in the resistance of duodenal ulcers to H2 receptor antagonists or in recurrent ulceration after highly selective vagotomy?

Basal serum gastrin, integrated gastrin response to a meal, and integrated gastrin response to insulin induced hypoglycaemia were measured in 60 patients with duodenal ulcer before and after elective highly selective vagotomy to determine whether antral gastrin has a role in resistance to H2 receptor antagonist treatment which the patients had received before surgery or in the development of recurrent ulceration after vagotomy. The basal gastrin, integrated gastrin response to a meal, and the integrated gastrin response to insulin were similar in patients whose ulcers healed after H2 receptor agonist treatment or were refractory to at least three months of this treatment. The same parameters measured before or after highly selective vagotomy were similar in patients who eventually developed recurrent ulceration compared with those who did not. As expected the basal and meal stimulated (but not insulin stimulated) serum gastrin values increased after highly selective vagotomy. Ulcer patients with particularly high gastrin values (whether basal or stimulated) were not more resistant to H2 receptor antagonist treatment or prone to develop ulcer recurrence after highly selective vagotomy. This study suggests that antral gastrin is not important in 'resistance' of duodenal ulceration either to H2 receptor antagonist treatment or to highly selective vagotomy.     

Intracerebroventricular administration of cholecystokinin-8 elevates plasma pancreatic polypeptide levels in awake dogs

The effect of intracerebroventricular (ICV) administration of cholecystokinin-8 (CCK-8) (0.5, 1.0, 2.0, 4.0 micrograms) on plasma levels of pancreatic polypeptide (PP) was studied in conscious dogs. ICV administration of CCK-8 (1.0, 2.0, 4.0 micrograms) produced a rapid and transient elevation in plasma concentrations of PP. Peripheral muscarinic receptor blockade with atropine or truncal vagotomy abolished PP secretion induced by ICV CCK-8. Pretreatment with ICV atropine also prevented the elevation in plasma PP induced by CCK-8. Plasma levels of CCK-33/39, CCK-8, and gastrin were not affected by ICV CCK-8. Our results indicate that central administration of CCK-8 selectively elevated plasma PP concentration. Since the effect of CCK-8 on plasma PP was abolished by central and peripheral atropine pretreatment, as well as by vagotomy, central and peripheral vagal cholinergic mechanisms appear to participate in release of PP that is induced by CCK-8 given by ICV injection.     

Effects of stimulation of the hypothalamic area on pancreatic exocrine secretion in dogs

The effects of electrical or chemical (0.1 M dl-homocysteic acid) stimulation of the hypothalamus on pancreatic exocrine secretion were studied in chloralose-anesthetized and hemispherectomized dogs whose pyloric sphincter had been ligated. Excitatory pancreatic flow responses with frequently increased antral contractility and small changes in blood pressure were induced by stimulation of the ventral and dorsal portions of the anterior hypothalamic area, the lateral part of the middle hypothalamus, and the mamillary body. The inhibitory pancreatic responses with reduced antral and corpus contractility and elevated blood pressure were elicited by stimulation of the posterior hypothalamic area, the middle portion of the anterior hypothalamus and the most dorsal area of the hypothalamus. Both excitatory and inhibitory responses were obtained even in dogs with cervical cord transection. The excitatory responses and some of the inhibitory ones were abolished by vagotomy or atropine, but some inhibitory responses remained even after vagotomy. These results indicate that hypothalamic stimulation induced both excitatory and inhibitory responses in pancreatic exocrine secretion via the vagus and other routes.     

Gastric manometric abnormalities in patients with dyspeptic symptoms after fundoplication.

We describe six patients in whom severe dyspeptic symptoms developed after fundoplication. The symptoms began immediately after operation (three patients) or shortly thereafter (three and eight months). There were no other known predisposing factors to gastroparesis. Seven, age-matched, healthy volunteers served as controls. Pressure activity from antrum (two sites), duodenum (two sites), and jejunum (one site) was recorded by a low compliance perfusion system connected to external strain gauge transducers. Activity was recorded for three hours during fasting and for two hours after the ingestion of a solid and a liquid meal. To determine whether an inadvertent vagotomy had been performed, basal acid output and the response to insulin (Hollander's test) were measured on a separate day. Manometric studies revealed postprandial hypomotility in these patients, whereas fasting antral and intestinal activities were normal. Acid output increased in all patients during insulin induced hypoglycaemia. In three patients, an antrectomy was subsequently performed, and they were relieved of their symptoms. We conclude that, after fundoplication, symptoms associated with postprandial antral hypomotility may develop in some patients. The pathophysiologic mechanism is unknown, but a positive acid response to insulin induced hypoglycaemia does not support the occurrence of incidental vagotomy. We do not know the prevalence of this motor abnormality among asymptomatic patients with prior fundoplication. A favourable symptomatic response to antrectomy in several of our patients, however, suggests that the symptoms were related to antral motor dysfunction.     

Nervous control of gastric and pancreatic secretory response to 2-deoxy-D-glucose in the dog

The relative contribution of the vagus and splanchnic nerves as mediators of the action of 2-deoxy-D-glucose (2-DG) on the stomach and the pancreas is largely unknown. In conscious dogs with gastric and pancreatic fistulas, the effect of 2-DG (100 mg kg-1, given as an intravenous bolus) on gastric acid and pancreatic exocrine secretion was tested before and after bilateral truncal vagotomy and after truncal vagotomy plus celiac and superior mesenteric ganglionectomy (i.e. extrinsic denervation of the stomach and the pancreas). In another set of dogs, only ganglionectomy was performed and the same experiments were done as in the first set of dogs. With the extrinsic nerves intact, 2-DG caused a rapid (within 15 min) and prolonged increase in gastric acid output as well as in pancreatic flow rate, bicarbonate and protein output. Truncal vagotomy abolished the gastric acid and pancreatic secretory response to 2-DG; additional ganglionectomy had no further effect. Ganglionectomy alone did not significantly alter 2-DG-stimulated gastric acid output, pancreatic flow rate and bicarbonate output; protein output, however, was significantly diminished by 57%. These results indicate that (a) intravenous 2-DG is a potent stimulant of gastric acid and pancreatic bicarbonate and protein output; (b) the vagus nerves are the major mediators of the gastric and pancreatic secretory response to 2-DG; (c) the sympathetic nerve fibers running through the celiac and superior mesenteric ganglia are probably not involved in the mediation of the 2-DG-induced gastric acid and pancreatic bicarbonate secretion. The diminished protein response to 2-DG after ganglionectomy is probably due to cut vagal fibers running through these ganglia.     

Relationship between insulin- and histamine-stimulated gastric secretion before and after vagotomy.

The relationship of gastric secretion in response to a single injection of insulin and in response to a histamine infusion, in unoperated patients with duodenal ulcer was studied before and after vagotomy. The secretion in response to insulin was significantly less than that in response to histamine. The ratio was about 0.7 before vagotomy, and about 0.4 after vagotomy irrespective of the adequacy of vagotomy. Highly significant correlations were obtained between the responses to the two stimuli, both in the unoperated group and in the whole postoperative group as well as in the inadequate vagotomy group, but not in patients after adequate vagotomy. Thus, the proportional differences between individuals in response to insulin were substantially the same as the proportional differences in response to histamine. The algebraic excess of histamine- over insulin-stimulated secretion before vagotomy did not differ from the value after vagotomy. Histamine-stimulated secretion after adequate vagotomy approximated to, but after inadequate vagotomy was greater than the preoperative algebraic excess of histamine- over insulin-stimulated secretion. These results are consistent with a new model of acetylcholine/histamine-receptor relationships. A certain proportion of the parietal cells are insensitive to the vagus but sensitive to histamine; and those sensitive to the vagus are also sensitive to histamine, but only when their vagal innervation is intact.