POTENTIATION BETWEEN URECHOLINE AND GASTRIN EXTRACT AND BETWEEN URECHOLINE AND HISTAMINE IN THE STIMULATIONS OF HEIDENHAIN POUCHES

Pentapeptide infusion test

Pentapeptide infused intravenously in graded doses provoked at a dose of 1.5 microg per kg per hour a peak HCl output, which was significantly higher than the HCl secretion induced by intravenous histamine in a dose of 40 microg per kg per hour in five healthy subjects. Pentapeptide infusion test at a dose of 1.5 microg per kg per hour appears to be a very reproducible and safe mode of gastric stimulation, giving a sustained and high level of gastric secretion in 20 subjects, including 10 healthy men and 10 duodenal ulcer patients. Infusion test with pentapeptide has some advantage over histamine stimulation in so far as it is safe, and almost completely free of side-effects. No difference in the response curves to pentapeptide and histamine was found between the normal subjects and duodenal ulcer patients.

Effect of bethanechol on gastric functions in primary anorexia nervosa

We have shown previously that patients with primary anorexia nervosa (PAN) have decreased gastric emptying and acid output. The present studies were designed to explore the possibility that bethanechol, a parasympathomimetic agent, would acutely restore normal gastric function in those patients. We used a dye dilution technique to determine acid output and fractional emptying rate in 5 patients with PAN and 11 healthy controls during a basal period and following bethanechol (0.06 mg/kg, subcutaneously). Although bethanechol caused fractional emptying and acid output to increase threefold in PAN (P less than 0.05), it failed to produce stimulation of gastric emptying and acid output to levels similar to those achieved in controls. Therefore, gastric emptying and acid output were less in PAN than in controls, both basally and after bethanechol. Since bethanechol failed to completely restore acute gastric function, the defect of emptying and acid output in PAN does not appear to be caused by a deficiency of parasympathetic neurotransmitter but, instead, could reflect undetermined inhibitory influences or impaired function of the muscular and glandular cells. Following weight gain, fractional emptying rate and acid output were still slightly less in PAN patients than in controls, but the difference was statistically significant only for basal acid output.

Effect of two types of beta-adrenergic blockade on gastric acid secretion during pentagastrin stimulation in non-vagotomized and in vagotomized gastric fistula dogs

The effect of beta-adrenoceptor blockade by propranolol and practolol on submaximally pentagastrin-stimulated gastric acid secretion was studied in conscious non-vagotomized and in vagotomized gastric fistula dogs. Propranolol (0.5 mg/kg) intravenously augmented gastric acid output in vagotomized dogs, more after truncal and selective vagotomy than after parietal cell vagotomy. Vagally innervated dogs also showed an increase, but to a lesser degree and not statistically significant. The increase restored the acid output to preoperative levels in the vagotomized dogs. Practolol (1.0 mg/kg) intravenously resulted in a slight and insignificant increase in acid output in dogs with truncal vagotomy and had only a negligible effect in vagally innervated dogs and after selective and parietal cell vagotomy. It is concluded that propranolol augments pentagastrin-stimulated acid output in vagotomized dogs, and this augmentation was most pronounced in the totally vagotomized stomach. Practolol had minor influence on gastric acid secretion. This effect of the two beta-blocking agents indicates that beta 2-blockade is most important for the secretory augmentation. The restoration of postvagotomy acid secretion to preoperative levels suggests that adrenergic influence is important for the decrease in pentagastrin-stimulated acid secretion after vagotomy.

Acid secretion by isolated canine gastric mucosa

1. An isolated gastric mucosal preparation from the dog stomach which is capable of acid secretion is described. Average values for normal resting potential difference (p.d.) was 49 +/- 2 mV (mucosal side negative with respect to the serosal side), short-circuit current (Isc) was 172 +/- 4 muA and resistance (R) was 285 +/- 6 omega.cm2. Low rates of spontaneous acid secretion (0-0.58 muequiv/cm2.hr) were present initially but following short-circuiting of the tissue these values decreased to low levels (less than 0.1 muequiv/cm2.hr) within an hour. 2. Histamine in doses exceeding 10(-6)M stimulated acid secretion, increased Isc and decreased R. Concentrations ranging from 10(-5) to 8 X 10(-4)M produced maximal secretion. The maximal secretory rate achieved was 4.24 +/- 0.35 muequiv/cm2.hr. 3. Pentagastrin (10(-8)M) and acetylcholine (10(-6)--10(-5)M) also stimulated acid secretion with a lower maximal secretion as compared to histamine stimulation. These concentrations of pentagastrin and acetylcholine did not alter histamine stimulated acid secretion. Higher concentrations of pentagastrin (10(-6)M) and acetylcholine (10(-4) M) reversibly inhibited acid secretion of histamine stimulated mucosa. 4. These results demonstrate that there are many similarities between in vitro and in vivo findings on the dog stomach, indicating the great potential of the in vitro dog gastric mucosa for studies on the mechanism of action and interaction of gastric secretagogues.

A comparison between intragastric titration and aspiration technique under basal conditions and after food or pentagastrin stimulation

A total of 16 healthy subjects had gastric secretory studies where acid was either measured by the conventional aspiration technique (AT) or by intragastric titration at a pH of 5.0 (IT). In a first study food- and pentagastrin-stimulated PAO levels, both measured by IT, were within similar ranges. However, as compared to the respective AT data of the same subjects, the mean IT results were 35% higher, although both values were well correlated. In a second study a similar difference was observed between IT and AT data throughout the whole range of the pentagastrin dose-response curve. Both curves followed Michaelis-Menten kinetics and had similar Km values, while Vmax values were significantly higher at IT. This constellation excludes an increase of the gastrin sensitivity of the parietal cells as a cause for the higher IT data. It is, however, in keeping with the hypothesis that the distension stimulus present at IT potentiates the pentagastrin-stimulated acid secretion. It is likely that methodological problems such as overtitration of acid at IT and transpyloric loss of acid at AT additively contribute to the relatively large difference between AT and IT values. It is therefore not possible to fully interchange AT and IT data, despite their good correlation.

The interaction of histamine with gastrin and carbamylcholine on oxygen uptake by isolated mammalian parietal cells

Using oxygen uptake as an index of the physiological response of isolated parietal cells, the interactions between histamine and gastrin and between histamine and carbamylcholine and the effects of atropine and metiamide on these interactions have been studied. Parietal cells were isolated from canine fundic mucosa by sequential exposure of separated mucosa to collagenase and EDTA. In previous studies carbamylcholine, isobutyl methyl xanthine, gastrin, and histamine have each been shown to increase oxygen uptake by these cells. Isobutyl methyl xanthine greatly enhanced the histamine effect. Carbamylcholine was inhibited by atropine but not by metiamide, histamine was inhibited by metiamide but not by atropine, and gastrin was inhibited by neither, suggesting that each of these agents has a direct action on the parietal cell. In the present studies, potentiating interactions between histamine and carbamylcholine and between histamine and gastrin have been demonstrated. Against a histamine (0.1 and 1 muM) plus isobutyl methyl xanthine (0.1 mM) background, the dose for 50% response for gastrin was approximately 1 nM, and the maximal response was obtained at 0.1 muM. When added to these combinations of stimulants, metiamide and atropine retained their respective specificities against stimulation by histamine and carbamylcholine, in that responses were inhibited to the level that was seen when the component of the pair that was not inhibited was given alone. The observation that histamine plus gastrin and histamine plus carbamylcholine produced maximal responses that were greater than the maximal response to histamine alone further supports the hypothesis that these agents each have direct actions on parietal cells. These observations are not consistent with the hypothesis that histamine is the sole mediator for the effects of other secretagogues. Furthermore, the inhibitory effects of atropine and metiamide on the specific cholinergic and histaminic components of the interactions that occur between secretagogues provide a possible explanation for the apparent lack of specificity of these agents on in vivo acid secretion.

The influence of graded distension and carbachol on the motor response to cholecystokinin in isolated guinea-pig antrum and fundus

Graded distension increased the motor response to cholecystokinin and acetylcholine both in antral and fundal pouches. The increase became even more obvious when the pressure responses were converted into changes in wall tension. The responses to cholecystokinin were additive with low doses (10(-7)M) of carbachol, but diminished or abolished by prestimulation with higher doses. The results indicate that the increased response to cholecystokinin after distension is due to increased smooth muscle stretch.

Gastric acid secretion

Advances in the understanding of physiologic control of gastric secretion raise the hope that an effective nonsurgical therapy for peptic ulcer disease will be developed soon. This paper reviews these advances with special emphasis upon those aspects of hormonal control, cyclic nucleotide function, and histamine activity which may have therapeutic applications.

The influence of secretin on the secretion of pepsin in response to acid stimulants in the anaesthetized cat

Peptic secretion was studied in fasting anaesthetized cats in which the pylorus and common bile duct had been occluded to prevent the release of duodenal hormones which might stimulate or inhibit gastric secretion. Dilute acid was instilled into the stomach at intervals to aid recovery of gastric secretion and to preserve peptic activity. 2. Caerulein, histamine and N-methyl histamine did not increase the output of pepsin when given on their own. Desulphated caerulein was a weak peptic stimulant. 3. Two C.H.R. u./kg per hour secretin initiated pancreatic secretion, the volume of which increased progressively as the dose was increased by stages to 32 C.H.R. u./kg per hour. 4. Four C.H.R. u./kg per hour secretin did not increase the output of pepsin. Peptic secretion was stimulated by 8 C.H.R. u./kg per hour. A maximal output of approximately 2000 u. pepsin/15 min was obtained when 16 C.H.R. u./kg per hour was infused. 5. When each acid stimulant was infused along with 4 C.H.R. u./kg per hour secretin the output of pepsin increased significantly. The peak output, which usually occurred between 15 and 30 min after stimulation, did not exceed 1000 u. pepsin/15 min. 6. The proposed explanation for the potentiation of the peptic response when an acid stimulant is infused along with a dose of secretin, in itself below the threshold of peptic stimulation, is that each acid stimulant increases gastric mucosal blood flow, approximately doubling the effective concentration of secretin delivered to the peptic cell.

Chemical stimulatory mechanism in gastric secretion

1. The serum gastrin level, gastric mucosal blood flow and acid secretion from the canine Heidenhain pouch have been measured in response to the introduction of bovine serum albumin, pepsin-digested albumin, an amino acid mixture, liver extract and mannitol used as control. 2. Distention of the Heidenhain pouch with mannitol or albumnin at pH 5-0 produced a similar pressure-related increase of acid secretion reaching a peak of only 10 percent of the maximal response to histamine. Pepsin-digested albumin was capable of producing larger acid outputs than undigested albumin. The highest acid output, attaining about 80 percent of the maximal response to histamine, was obtained with liver extract both before and after exhaustive dialysis to remove all the amino acids and short peptide fragments. An amino acid mixture containing all essential amino acids was also found to stimulate acid secretion but a lesser degree than liver extract. 3. This concluded that it is not the intact protein but the products of its digestion, the polypeptides and free amino acids, which are potent chemical stimulants of acid secretion from the oxyntic gland area. Since the serum gastrin level was not changed during acid secretion induced by peptic digests bathing the oxyntic gland area, the mechanism of chemical stimulation appears to be gastrin-independent. 4. The response to chemical stimulation by peptic digests can be greatly potentiated by combining this with distention of the oxyntic gland area. Topical application of xylocaine or atropine causes a marked decrease of Heidenhain pouch response to peptic digests, suggesting a possible neural reflex component in the mechanism of chemical stimulation of the oxyntic gland area. 5. When the pH of the liver extract in the Heidenhain pouch was gradually decreased in sequential order from 5-0 to 1-0, this resulted in a pH-related decrease in acid secretion and in the mucosal blood flow falling to the basal level at pH 1-0. Exogenous secretion given in graded doses from 0-5 to 8-0 u./kg. hr caused a small but dose-related inhibition of acid response to liver extract accompanied by a decrease of mucosal blood flow but without any significant change in the serum gastrin level. 6. The results indicate that the chemical stimulation of the oxyntic gland area by peptic digests is capable of inducing acid secretion by a local, gastrin-independent, partially neural reflex mechanism; sensitive to pH, pressure and secretin.

Secretin and cholecystokin-pancreozymin in combination in the inhibition of gastric acid secretion

Both secretin, and the single substance which possesses both cholecystokinin and pancreozymin activity, have been shown to inhibit gastric acid secretory responses. Since potentiation may occur between pairs of stimulants of gastric secretion, the effects of combining secretin and cholecystokinin/pancreozymin have been studied in Heidenhain pouches stimulated by continuous intravenous pentagastrin. Evidence suggesting potentiation between these two inhibitor agents is presented.

Rat gastric acid secretion studies with histamine and synthetic gastrin-like pentapeptide

1. Gastric acid secretion was measured in the urethane anaesthetized rat whilst maintaining a recirculated gastric perfusion fluid at pH 4.2. The latent period of onset of secretion following single intravenous doses of histamine and pentapeptide in combination was significantly shorter than that following either stimulant alone.3. When administered over a period of 2 hr the maximal steady rate of secretion in response to pentapeptide was 75% of that to histamine.4. Acid stimulatory effects were additive both when the drugs were given concurrently over a 2 hr period and when one was administered after a maximal response had been obtained to the other.5. Although there is some evidence to indicate that histamine and pentapeptide might be initiating acid secretion by different mechanisms it is suggested that they may not be acting with total independence.

Maximal acid response of Pavlov pouches to food and histamine

Secretion of gastric acid in response to histamine, insulin, and a meal of liver, with and without 5% bone dust, was studied in three dogs with Pavlov pouches and gastric fistulas. The ratios of insulin-induced to histamine-induced secretion were the same in pouch and main stomach indicating that their innervation was equivalent. Meals of a liver and bone dust mixture in amounts of 11 to 44 g/kg resulted in Pavlov pouch acid outputs that were 34 to 56% higher than the maximal response to histamine (p < 0.05 to < 0.001). Liver without bone dust also produced higher acid outputs than histamine. These results indicate that combinations of endogenously generated stimuli can produce a potentiated gastric response which exceeds that produced by histamine alone.

Latency of the gastric secretory response to sham feeding in the dog

In conscious dogs with gastric fistulas the latency of both the gastric acid and pepsin responses to sham feeding was about 6 min. When a background secretion was induced with various closes of hog gastrin, the latency of the acid response to sham feeding was unchanged, but the latency of the pepsin response was shortened. The peak rates of acid and pepsin secretion after sham feeding were not altered by the infusion of gastrin.