N. Kwiecien

Cholecystokinin in the inhibition of gastric secretion and gastric emptying in humans

Cholecystokinin (CCK) is known to inhibit gastric acid secretion and gastric emptying but its physiological role in the inhibition of gastric functions is not settled. In this study performed on 16 young male subjects, gastric acid secretion and emptying rate were determined after intragastric administration of 8% peptone meal alone or in combination with intravenous infusion of graded doses of CCK-8 (5-80 pmol/kg.h) or with addition of vegetable oil to meal without or with pretreatment with loxiglumide, a specific CCK antagonist. CCK-8 infusion at lower dose (5 pmol/kg.h) was ineffective but at higher doses (20-80 pmol/kg.h) it resulted in a significant reduction in acid output by 39 and 43% and a decrease in gastric emptying from 54% to 40 and 22%, respectively. Pretreatment with loxiglumide abolished almost completely the inhibition of both gastric acid and gastric emptying by CCK-8. Fat added to peptone meal reduced gastric acid secretion by 42-65% and decreased gastric emptying to 24-32%. The pretreatment with loxiglumide tended to reduce fat-induced inhibition of gastric acid secretion and gastric emptying but the difference in the inhibition of gastric functions between the tests without and with loxiglumide was not significant. This study provides evidence that exogenous CCK administered at pharmacological doses is a potent inhibitor of gastric acid secretion and gastric emptying and probably acts via specific CCK receptors. In contrast, fat induces inhibition of gastric acid secretion and gastric emptying that cannot be fully attributed to hormonally acting CCK.

Effect of somatostatin on meal-induced gastric secretion in duodenal ulcer patients.

The effect of somatostatin, a growth hormone release-inhibiting hormone (GH-RIH), on basal and meal-, pentagastrin-, or histamine-stimulated gastric acid and pepsin secretion was studied in six duodenal ulcer patients. Intravenous GH-RIH infused in graded doses ranging from 0.62 to 5.0 μg/kg/hr produced a dose-related inhibition of pentagastrin-induced acid secretion reaching about 15% of control level at the dose of 5.0 μg/kg/hr. Acid inhibition was paralleled by a decrease in the pepsin output and accompanied by a dosedependent reduction in serum growth hormone and insulin levels measured by radio-immunoassay. GH-RIH used in a single dose of 2.5 μg/kg/hr produced about 85% inhibition of acid secretion induced by a meal (measured by intragastric titration) accompanied by a significant decrease in serum gastrin and insulin levels. The effect of GH-RIH on histamine-stimulated secretion was very modest and observed only after stopping the GH-RIH infusion. Thus GH-RIH suppressed acid and pepsin secretion induced by pentagastrin and a meal, and this effect was accompanied by a suppression of serum growth hormone and gastrin levels which may contribute to the inhibition of gastric secretion observed.

Prostaglandins and Vagal Stimulation of Gastric Secretion in Duodenal Ulcer Patients

The effects of a stable prostaglandin (PG) E2 analog (15-R-15 methyl PGE2) and aspirin, a potent inhibitor of cyclooxygenase, on modified sham-feeding (MSF)-stimulated gastric secretion and serum gastrin and pancreatic polypeptide (PP) levels were measured in patients with duodenal ulcer. PGE2 analog given orally significantly reduced gastric acid and pepsin secretion and suppressed serum PP but not gastrin responses to MSF. Suppression of PG generation in the gastric mucosa did not influence the secretory or hormonal responses to MSF. This study shows that endogenous PGs are not involved in the control of vagally stimulated gastric secretion, but exogenous PGE2 analog is an effective inhibitor of such secretion and merits clinical evaluation in the treatment of duodenal ulcer.

Effect of orally administered 15(R)-15-methyl prostaglandin E2 and/or an anticholinergic drug on meal-induced gastric acid secretion and serum gastrin level in patients with duodenal ulcers.

The purpose of the present series of tests was to measure and compare the effects of ingestion of gelatin capsules containing 15(R)-15-methyl PGE2 (PG) and/or an anticholinergic drug (methscopolamine bromide, Pamine) on meal-induced gastric acid secretion and serum gastrin level. Eleven duodenal ulcer patients were stimulated by a 5% peptone meal. Acid secretion was determined by the intragastric titration technique, and serum gastrin was measured by radioimmunoassay. The tests were randomized and double-blind. PG alone given 30 min before a test meal at a dose of 50 micrograms or 100 micrograms produced no side effects and inhibited meal-stimulated acid secretion by about 43% and 55%, respectively. Gastric acid inhibition after a single dose of PG was most pronounced in the first hour of a test meal and was accompanied by almost complete suppression of the meal-induced serum gastrin level. Pamine alone in a dose of 2.5 mg reduced gastric acid response to a meal by about 29% but caused a further rise of postprandial serum gastrin level over control values. The combination of PG, 50 micrograms, and Pamine, 2.5 mg, did not result in significantly greater acid inhibition (about 48%) than when either compound was given alone. When the higher dose of PG (100 micrograms) was given together with Pamine (2.5 mg), the degree of inhibition produced by PG alone was not changed. It is concluded that PG given orally in capsules is a potent inhibitor of gastric acid and serum gastrin response to a meal and that this effect may be of potential value in the treatment of peptic ulcer disease.

Effects of Protective Drugs on Gastric Alkaline Secretion in Man

This study was designed to determine the effects of sucralfate, De-Nol, and Maalox 70 on gastric HCO3 secretion in 34 healthy humans. Alkaline secretion was measured after pretreatment with ranitidine to abolish H+ secretion, using a constant perfusion-aspiration system and back-titration of the perfusates to the original pH 6.0. Luminal release of PGE2 was also measured in the gastric perfusates. Addition of sucralfate or De-Nol resulted in increments of gastric HCO3 secretion, reaching about 45% and 59%, respectively, of the maximal HCO3 response to 16,16-dimethyl PGE2 (dmPGE2). The highest response to Maalox 70 reached about 21% of dmPGE2 maximum. These effects of sucralfate, De-Nol, and Maalox 70 were accompanied by a significant increase in luminal release of PGE2. Pretreatment with atropine reduced basal and, in part, sucralfate-, De-Nol-, and Maalox 70-induced alkaline secretion, whereas pirenzepine did not affect this secretion. Aspirin reduced the release of PGE2 by about 80% and suppressed almost completely the gastric HCO3 response to sucralfate, De-Nol, and Maalox 70. This study provides evidence that sucralfate, De-Nol, and Maalox 70 stimulate gastric alkaline secretion via a prostaglandin-dependent mechanism.

Effects of Colloidal Bismuth Subcitrate on Aspirin-Induced Gastric Microbleeding, DNA Loss, and Prostaglandin Formation in Humans

Ten healthy young male subjects took part in a double-blind, placebo-controlled, crossover trial to assess the effect of colloidal bismuth subcitrate (De-No) on prostaglandin (PG) E2 generation and mucosal integrity in an aspirin (ASA)-treated stomach. After administration of ASA (2.5 g) plus placebo, a marked reduction in mucosal generation of PGE2 (by about 85%) was observed, and this was accompanied by a significant increase in gastric microbleeding and DNA loss and endoscopic and histologic damage of the mucosa. After the combination of De-Nol (300 mg four times daily) with ASA, mucosal generation of PGE2 showed a reduction similar to that in tests with ASA plus placebo, but gastric microbleeding and mucosal damage were significantly reduced. It is concluded that De-Nol has a protective action on ASA-induced gastric microbleeding and that this protection occurs despite a marked suppression of mucosal production of prostaglandins.

Effects of Nocloprost on Gastric Functions in Man

Previous studies in animals and humans demonstrated that nocloprost, a stable prostaglandin E2 analogue, shows very high gastroprotective potency, relatively weak gastric inhibitory activity, and low systemic bioavailability after oral administration. In this study the effects of nocloprost on gastric acid secretion and intraluminal pH and on gastric emptying and plasma gastrin levels were determined in humans. Nocloprost at doses of 50 and 100 micrograms was ineffective, but at a dose of 200 micrograms it reduced the response to pentagastrin significantly and that to a peptone meal by 30-50% and abolished plasma gastrin response without affecting the rate of gastric emptying. Nocloprost given at a dose of 100 micrograms three times daily 30 min before the major meals (breakfast, lunch, and dinner) did not affect intragastric pH significantly as monitored by continuous intraluminal pH-metry. We conclude that nocloprost does not affect gastric acid secretion or intraluminal pH when applied at a dose (50-100 micrograms) that is gastroprotective and that is proposed for peptic ulcer therapy. A higher dose (200 micrograms) of nocloprost causes moderate gastric acid inhibition and suppression of plasma gastrin release without affecting gastric emptying or causing any side effects.

Gastric Protection by Nocloprost against Aspirin Damage in Humans Possible Role of Epidermal Growth Factor

Ten healthy young male subjects took part in a double-blind, placebo-controlled crossover study to assess the effects of nocloprost on gastric microbleeding and endoscopic mucosal injury induced by the administration of aspirin (2.5 g). In addition, basal and pentagastrin-induced gastric acid and pepsin secretion and salivary and plasma contents of epidermal growth factor (EGF) were measured after placebo plus aspirin or nocloprost plus aspirin treatment in these subjects. Nocloprost (100 micrograms/dose) significantly reduced spontaneous gastric microbleeding and almost completely prevented gastric mucosal injury induced by aspirin. Nocloprost failed to affect basal and pentagastrin-stimulated gastric acid and pepsin secretion but increased significantly the salivary outputs and plasma concentrations of EGF. In conclusion, nocloprost is effective in preventing gastric injury by aspirin even at a non-antisecretory dose, and this protection may involve an excessive release of EGF.

Experimental and clinical studies on the prevention of aspirin-induced gastric damage by “cytoprotective” drugs

Experimental studies initiated by Robert and co-workers1,2 have demonstrated that a number of prostaglandins (PGs) given exogenously or released endogenously by “mild irritant” in the stomach3, prevent gross mucosal lesions caused by various necrotizing substances.