The role of the beta-adrnergic receptor in the secretion of gastrin: studies in normal subjects and in patients with duodenal ulcers

Use of beta-blockers and risk of serious upper gastrointestinal bleeding: a population-based case-control study

BACKGROUND

Some studies indicate a reduced risk of serious upper gastrointestinal bleeding (UGIB) for users of beta-blockers, but the association remains to be confirmed in larger studies and characterized with respect to differences among beta-blockers. We aimed to assess whether beta-blocker use decreases the risk of UGIB.

METHODS

We conducted a register-based, population-based case-control study in Denmark. We identified cases with a first validated discharge diagnosis of UGIB during the period 1995-2006. Controls were selected by risk-set sampling in a ratio of 10:1. We estimated crude and adjusted odds ratios (ORs) of the association between current beta-blocker use and the risk of UGIB by using conditional logistic regression and further stratified by selective and non-selective beta-blockers, respectively.

RESULTS

We identified 3571 UGIB cases and 35,582 controls. Use of beta-blockers was not found to be associated with a decreased risk of UGIB (adjusted OR 1.10; 95% CI: 1.00-1.21). The association remained neutral after stratification by selective and non-selective beta-blockers, and by single beta-blocker substances. Similarly, we found no association between current beta-blocker use and the risk of UGIB within different subgroups.

CONCLUSIONS

We found no association between beta-blocker use and UGIB.

The role of catecholamines in clinical medicine

The sympathetic nervous system is of major importance for the regulation of several physiological functions. Drugs which inhibit the actions of catecholamines and adrenergic drugs are used in the treatment of many clinical disorders. The potential role of catecholamines in a number of human diseases has, however, until recent years been studied to a limited extent only due to lack of methods for quantitation of sympathetic nervous activity. After the development of enzymatic isotope-derivative assays, reliable measurements of noradrenaline and adrenaline in plasma became available. Studies in man have shown that plasma noradrenaline is an index of sympathetic nervous activity. The present survey deals with sympathetic nervous activity and plasma adrenaline in a number of clinical disorders viz. arterial hypertension, duodenal ulcer, thyrotoxicosis, diabetes mellitus and ketotic hypoglycemia.

Antihypertensive drugs and the risk of gastrointestinal bleeding

PURPOSE

Calcium channel blockers have been reported to increase the risk of gastrointestinal bleeding. We tested this hypothesis, and also assessed whether beta blockers decrease this risk.

SUBJECTS AND METHODS

A nested case-control design within a population-based cohort of all 34,074 new users of beta blockers, angiotensin-converting enzyme (ACE) inhibitors, or calcium channel blockers in Saskatchewan, from 1990 to 1993 and followed up to March 1995, was used. We identified all 311 subjects hospitalized because of gastrointestinal bleeding during this period, each of whom was matched to 10 randomly selected controls.

RESULTS

The rate of hospitalization for gastrointestinal bleeding was 3.0 per 1,000 per year. The adjusted rate ratio of gastrointestinal bleeding for current use of calcium channel blockers was 1.1 (95% confidence interval [CI] 0.8 to 1.4) and 0.66 (95% CI 0.44 to 0.98) for beta blockers compared with no current use of anti-hypertensive drugs. The adjusted rate ratio for ACE inhibitor use was 1.0 (95% CI 0.7 to 1.3) while that for diuretic use was 1.4 (95% CI 1.0 to 2.0).

CONCLUSIONS

The use of calcium channel blockers does not appear to increase the risk of gastrointestinal bleeding in the first five years of treatment, while beta blockers may prevent this adverse event. The unexpected elevated risk associated with the use of diuretics needs to be investigated further.

Functional and molecular evidence for beta 1-, beta 2- and beta 3- adrenoceptors in human colon

1. Relaxation of carbachol pre-contracted human colonic muscle to (-)-isoprenaline was examined in circular, longitudinal and taenia coli preparations to determine the beta-adrenoceptor subtypes involved. beta 1-, beta 2- and beta 3-Adrenoceptor mRNAs were also measured in colonic muscle and mucosa. 2. (-)-isoprenaline caused relaxation of longitudinal smooth muscle preparations with pEC50-7.39 +/- 0.12, and this response was inhibited by both propranolol (0.1 microM, pKB 8.55 +/- 0.12) and the selective beta 1-antagonist, CGP 20712A (0.1 microM, pKB 8.80 +/- 0.20), while the selective beta 2-antagonist, ICI 118551 (0.1 microM) failed to inhibit isoprenaline relaxation consistently. 3. (-)-Isoprenaline caused relaxation of taenia coli with a pEC50 of 6.70 +/- 0.17. Propranolol (0.1 microM). CGP 20712A (0.1 microM) and ICI 118551 (0.1 microM) inhibited the isoprenaline response with similar low affinities (pKB values 7.93, 7.71 and 7.54, respectively). Carbachol pre-contracted circular smooth muscle preparations failed to relax consistently to isoprenaline and these responses were not characterized. 4. beta 1- and beta 2-Adrenoceptor mRNAs were present in circular longitudinal muscle samples and taenia coli samples, and lower levels were detected in mucosa. beta 3-mRNA was also present in both muscle preparations but was not detected in human colonic mucosa. 5. In summary, beta 1-adrenoceptors are the predominant subtype mediating isoprenaline-induced relaxation of the thin longitudinal smooth muscle of human colon, while beta 1-receptors do not appear to be involved in these responses. However, beta 3-adrenoceptors may play a role in relaxation of the taenia coli as conventional antagonist affinities are low. beta 3-Adrenoceptor mRNA was present in taenia coli and circular/longitudinal smooth muscle but absent from human colonic mucosa.

Effect of propranolol on secretin-induced gastrin release and secretin-induced tachycardia in patients with the Zollinger-Ellison syndrome

The mechanism for secretin-induced gastrin release in the Zollinger-Ellison syndrome is uncertain. We evaluated whether the stimulatory effect of intravenous secretin on gastrin release was partly mediated through a beta-adrenergic stimulatory mechanism. Serum gastrin concentrations and heart rate were monitored in six patients with the Zollinger-Ellison syndrome. Secretin (2 clinical units/kg) increased mean serum gastrin concentrations from 1558 pg/ml basally to a peak of 3683 pg/ml (136% above baseline). This increase was not altered by pretreatment with 2 mg of propranolol intravenously, a dose which in previous studies blocked terbutaline-induced gastrin release. Secretin increased heart rate by 14 beats/min (20% above base-line) and this also was not altered by propranolol pretreatment. Thus, the stimulatory effects of secretin on gastrinoma cells and the heart do not appear to be mediated by beta-adrenergic receptors.

Role of circulating catecholamines in the control of pancreatic polypeptide and gastrin release

The influence of circulating catecholamines on the release of pancreatic polypeptide (PP) and gastrin was studied in volunteers. Physical exercise increased plasma epinephrine by 374 +/- 123% and plasma norepinephrine by 167 +/- 30%, but plasma PP concentrations remained unchanged during standardized bicycle ergometry. Immediately after cessation of exercise catecholamine levels decreased rapidly, whereas PP concentrations increased by 55%. In a second series, epinephrine infusion (5, 25, and 75 ng.kg-1.min-1) increased epinephrine levels by 38 +/- 12, 331 +/- 69, and 1229 +/- 131%, respectively, whilst norepinephrine was unaffected. Neither during nor after catecholamine infusion PP secretion was affected. Gastrin release increased by a maximum of 85 +/- 38% (at epinephrine 75 ng.kg-1.min-1). It is concluded, that (1) changes in circulating adrenaline do not significantly influence PP secretion in man; (2) the PP increase immediately following physical exercise cannot be attributed to a rapid fall of catecholamine levels; (3) endogenous catecholamines are of minor importance in the control of gastrin secretion.

Increased serum pancreatic polypeptide and serum gastrin secretion in patients with functional dyspepsia: correlation to the shape of the duodenal loop

Simultaneous measurement of food-stimulated serum pancreatic polypeptide and serum gastrin was carried out in 18 patients with functional dyspepsia and correlated to the shape of the duodenal loop. Significantly higher serum concentrations of pancreatic polypeptide and gastrin were encountered in patients with an abnormal shape of the duodenal loop compared to patients with a normal shape. Although no cause could be given to the phenomenon it may be taken into account when evaluating hormone profiles in patients with functional dyspepsia.

Beta adrenergic influence on esophageal and colonic motility in man

Gastrointestinal (GI) motility is centrally controlled through the sympathetic and parasympathetic nerves, sympathetic effects being partly mediated by beta adrenoceptors. Although beta adrenoceptor agonists and antagonists are widely used for different disorders, little is known about the influence of these agents on GI motility. The present study was initiated to investigate whether there is a physiological, beta adrenergic influence on human GI motility and to describe the effects of selective beta adrenoceptor stimulation on motility in the proximal and distal parts of the GI tract. Esophageal peristalsis was measured in healthy subjects using electronic catheters. Distal colonic motility was measured with an open-tipped, water-perfused catheter in the sigmoid colon and from an air-filled balloon in the rectum in healthy subjects and in patients with the irritable bowel syndrome (IBS). In one study, colonic motility was stimulated with continuous infusion of the octapeptide of cholecystokinin (CCK-OP). Esophagus: Peristaltic amplitude was increased in the distal smooth muscle part of the esophageal body after infusion of both the nonselective beta blocker propranolol and the beta-1 selective blocker metoprolol. After infusion of the beta-1 agonist prenalterol and the beta-2 selective agonist terbutaline, a profound decrease in esophageal peristaltic amplitude was seen. Pretreatment with metoprolol selectively blocked the response to a moderate dose of prenalterol but did not block the response to terbutaline. The latter response was blocked by propranolol. Peristaltic velocity in the proximal part of the esophagus was decreased by beta-1 stimulation and in the distal part by beta-2 stimulation. Distal colon: In healthy subjects the sigmoid motility index showed a dose-dependent increase after metoprolol and propranolol, respectively. The increase was more marked after propranolol infusion. Terbutaline decreased the sigmoid motility index both in healthy subjects and in patients with the IBS. Furthermore, the rectal motility index was decreased in the group of healthy subjects. The effects of prenalterol on rectal and sigmoid motility did not differ from those of placebo. The IBS patient group showed larger intraindividual variations in sigmoid motility from day to day and also lower rectal motility indices than the healthy subjects. Infusion of CCK-OP increased the sigmoid motility index compared to non-stimulated conditions. No effects on CCK-OP stimulated motility were seen after either terbutaline, prenalterol or placebo.(ABSTRACT TRUNCATED AT 400 WORDS)

Beta-adrenergic blockade and the gastrointestinal system

As beta-adrenergic blockers grow increasingly popular for the therapy of a wide variety of disorders, it becomes increasingly important to appreciate the spectrum of physiologic effects on the gastrointestinal system and the potential hazards associated with use of these agents. This review details the effects of the beta-adrenergic blocking agents on the gastrointestinal tract.

Adrenergic control of rat gastric somatostatin and gastrin release

The effect of adrenergic agonists and antagonists on the secretion of gastric somatostatin-like immunoreactivity (SLI) and gastrin was investigated in an isolated, vascularly perfused rat stomach preparation. Two- to six-fold increases in SLI secretion induced by isoproterenol, epinephrine, and norepinephrine were completely abolished by propranolol but were not influenced by phentolamine. Propranolol did not alter glucagon- and DB-cAMP-induced stimulation of SLI release. Experiments in which the beta 2-agonist salbutamol and the beta 1- and beta 2-blockers practolol and H35/25 were used showed that both subtypes of beta receptors are involved. Gastrin secretion revealed only minor changes in dose-response studies with a wide range of isoproterenol concentrations (2 X 10(-8) to 1.5 X 10(-4) M). The results obtained in this study suggest that in rats 1) the SLI response to adrenergic agonism is predominantly mediated by beta receptors; 2) both beta 1- and beta 2-adrenergic receptors are involved; 3) under in vitro conditions, adrenergic agonism is a weak stimulus for gastrin secretion.

hPP and gastrin response to a liquid meal and oral glucose during prolonged severe exercise, caloric deficit, and sleep deprivation

Sixteen young healthy military cadets were subjected to prolonged severe exercise, caloric supply deficiency, and sleep deprivation during a 5-day ranger training course. Several cadets complained of gastric discomfort. The fasting and postprandial human pancreatic polypeptide (hPP) and gastrin levels induced by a liquid meal (no. = 9) and peroral glucose load (no. = 7) were measured during normal school activities (control) and on the third day during the course. The results showed that the fasting level of hhPP was significantly increased during the course. Both during meal and glucose stimulation the hPP level during the course was significantly higher at most registrations than during control conditions. The fasting level of gastrin was not changed. The maximal level of gastrin during meal stimulation was higher during the course than during the control period. Glucose loading, on the other hand, did not change the gastrin response. The integrated response of hPP and gastrin were not changed during the course either for the liquid meal or for the peroral glucose load.

Reflex activation of the sympatho-adrenal system inhibits the gastrin release caused by electrical vagal stimulation in cats

The present study on anesthetized cats was performed to investigate how vagally induced gastrin release is influenced by simultaneous activation of the sympatho-adrenal system. The gastrin concentration in portal blood and in antral perfusates was measured with radioimmunoassay. The vagi were activated electrically and the sympatho-adrenal system by bilateral clamping of the carotid arteries. It was found that the vagally induced release of gastrin both into the circulation and into the antral lumen, was markedly inhibited (30% of control values) by simultaneous sympathetic activation, both at neutral and at acid intraantral pH. Infusions of adrenaline or noradrenaline did not mimick the effect on gastrin release induced by clamping of the carotid arteries. It is possible that the inhibitory effect of sympathetic activation on stimulated gastrin secretion is mediated via release of an inhibitory peptide, e.g. somatostatin, from the splanchnic nerves.

The effect of phenoxybenzamine on the gastrin response to glycine stimulation

The nature of adrenergic mechanism involved in gastrin release in response to local stimuli and feeding is still unclear. In the present study, the effect of phenoxybenzamine, a potent alpha-blocking agent, on the gastrin release in response to glycine perfusion (pH 7.0) of an isolated canine antral pouch was examined. The experiment was repeated with truncal vagotomy performed before glycine perfusion. It was found that gastrin concentrations measured via right gastroepiploic vein were significantly increased during phenoxybenzamine infusion with and without truncal vagotomy. This finding indicates the presence of an alpha-adrenergic mechanism which inhibits gastrin release when the antrum is locally stimulated. After the drug was discontinued, though there was an enhancement in gastrin response in both saline and glycine perfused groups, the peak gastrin levels were reached earlier in the vagotomized dogs. This finding might indicate the influence of vagus nerve during the experiment.

Effect of a beta 2-sympathomimetic on gastrin release, acid secretion, and blood glucose during basal conditions and in response to insulin, 2-deoxy-D-glucose, and feeding in the dog

The effect of a selective beta 2-adrenoceptor agonist on basal volume and on insulin-, 2-deoxy-D-glucose (2-DG)-, and food-induced gastrin release was studied in conscious gastric fistula dogs. Acid output and blood glucose changes were also studied, except in the food experiments. Basal acid secretion and serum gastrin were unchanged after beta 2-sympathetic infusion, whereas a slight increase in blood and glucose was found. The beta 2-agonist almost prevented acid output and gastrin release after insulin hypoglycaemia. However, the hypoglycaemia was also inhibited. Gastric acid secretion stimulated by 2-DG was inhibited, as was probably the gastrin release. 2-DG increased the blood glucose level, and no significant differences were found after beta 2 infusion. After feeding, gastrin release was initially decreased for one of five doses of the beta 2-agonist, and higher doses of the beta 2-agonist prevented the subsequent fall in serum gastrin after the initial peak value. This pattern was also found for the histamine H2-blocker cimetidine in a dose that blocks acid output. The beta 2-agonist and 2-DG increased pulse rate. It is concluded that beta 2-sympathetic stimulation inhibits acid output and gastrin release after insulin and 2-DG stimulation, but one should be cautions in drawing conclusions from the insulin experiments. The effect on gastrin release is small compared with the effect on the acid secretion, and it is unlikely that the inhibition of acid secretion acts through a change in gastrin release.

Abnormal duodenal loop demonstrated by X-ray. Relation to gastric emptying time

Gastric emptying time of a solid meal was estimated on X-ray in 7 patients with a normal duodenal loop, 7 patients with a proximal duodenal anomaly, and 12 patients with a distal duodenal anomaly. A determination coefficient between gastric emptying time and duration of serum gastrin increase was calculated. The food-stimulated serum gastrin secretory pattern was studied in 9 patients with a normal duodenal loop, 6 with a proximal duodenal anomaly, and 13 with a distal duodenal anomaly. The various groups presented significantly different gastric emptying times; thus patients with normal duodenal loop had a mean gastric emptying time of 6 h, patients with proximal duodenal anomalies ahd a mean gastric emptying time of 4.5 h, and patients with distal duodenal anomalies had a mean gastric emptying time of 9 h. Gastric emptying time and duration of increased serum gastrin secretion was positively correlated (R2 = 0.89). The food-stimulated serum gastric secretory pattern was equal in patients with proximal duodenal anomalies and those with distal duodenal anomalies and furthermore, reached significantly higher serum gastrin concentrations than in patients with a normal duodenal loop.

Reflex adrenergic gastrin release evoked by unloading of carotid baroreceptors in cats

Gastric acid and pepsin output in response to 0.10 and 6.0 microgram . kg-1h-1 of pentagastrin response to complete elimination of the carotid baroreceptor discharge by cutting the bilateral sinus nerves. Such unloading of the baroreceptors simulates a blood pressure drop to 50--60 mmHg, resulting in a pronounced reflex increase in the activity of the sympatho-adrenal system. Cutting the sinus nerves caused an increased level of immuno-reactive gastrin in the portal plasma, and this elevated gastrin concentration was virtually extinguished by bilateral adrenalectomy. We conclude that the carotid baroreceptors can influence the gastrin release by a reflex adjustment of the release of adrenal catecholamines.

Increased sensitivity of gastrin release to adrenaline in duodenal ulcer

Serum gastrin concentrations were measured in patients with duodenal ulcer and controls before, during, and after one-hour intravenous infusion of various doses of adrenaline (0.12 microgram to 6 microgram/min). Gastrin concentrations in the basal state were significantly increased in duodenal ulcer patients compared to controls. The maximal rise in serum gastrin concentrations was obtained at a dose of 4 microgram/min adrenaline in both groups of subjects, and the increase was significantly higher in duodenal ulcer patients than in controls. Adrenaline increased predominantly the gastrin III component (gastrin-17 like) in both duodenal ulcer patients and controls. The threshold level of adrenaline-induced gastrin release was significantly lower in duodenal ulcer patients: intravenous infusion of adrenaline in a dose of 0.12 microgram and 0.25 microgram/min increased serum gastrin concentrations 23 and 43%, respectively, but had no effect in controls. Rises in plasma adrenaline concentrations were similar in both groups of subjects in response to the various doses of adrenaline employed. Only the smallest dose of adrenaline (0.12 microgram/min) resulted in clearly physiological variations in plasma adrenaline concentrations. The results indicate that endogenous adrenaline may stimulate the secretion of gastrin during physiological conditions in patients with duodenal ulcer.

Increased plasma noradrenaline and serum gastrin in patients with duodenal ulcer

Serum gastrin, serum insulin, plasma noradrenaline, plasma adrenaline, pulse rate and blood pressure were measured repeatedly during 24h in six patients with duodenal ulcer and in six control subjects. Mean serum gastrin concentration was 3-4 times higher in duodenal ulcer patients than in controls during both the day and at night. Serum insulin was the same in both groups of subjects. Overnight fasting and mean supine plasma noradrenaline as well as mean supine pulse rate were significantly higher in duodenal ulcer patients than in controls. Plasma adrenaline and arterial blood pressure were the same in patients and controls. These results suggest that sympathetic nervous activity is increased in patients with duodenal ulcer. The increased sympathetic nervous activity may mean that duodenal ulcer patients are subject to more stress than normal subjects or may be compensatory to increased vagal nervous activity presumed by some authors to be present in such patients.

Hypogastrinemia in hypothyroidism

Fasting plasma gastrin levels measured by radoimmunoassay were found to be low in patients with hypothyroidism. The intravenous infection of arginine caused an increase of plasma gastrin in hypothyroid patients but was significantly lower than those in normal subjects. The decreased gastrin level in patients with hypothyroidism was significantly improved after the thyroid function was normalized by treatment.

The influence of an abnormal duodenal loop on basal and food-stimulated serum gastrin concentrations

Postprandial serum gastrin secretion was studied in 26 patients with X-ray-negative dyspepsia. Seven patients had a normal duodenum while 19 had duodenal anomalies. In patients with an abnormal duodenal loop, the mean postprandial serum gastrin secretion was significantly higher after 45, 60 and 120 min than that of the control group. No significant difference was demonstrated in the basal state. A delay in gastric emptying rate might be the cause of increased postprandial serum gastrin secretion in patients with an abnormal duodenal loop.

Inhibition of parathyroid hormone secretion by isoproterenol

Intravenous infusion of the beta-adrenergic agonist isoproterenol produced a fall in the serum concentration of parathyroid hormone. It also produced a pronounced fall in the serum phosphate concentration, and significant increases in blood glucose and serum insulin concentration and in pulse rate. The fall in serum parathyroid hormone was abolished by beta-adrenergic blockage with propranolol. Oral glucose loads produced a pronounced fall in serum phosphate concentration, comparable to the fall after isoproterenol infusion, but no significant changes in serum parathyroid hormone. It is concluded that the fall in serum parathyroid hormone after isoproterenol is due to a beta-adrenergic effect. It is unknown, if isoproterenol acts directly on the parathyroid hormone secreting cell, or the fall in serum parathyroid hormone is secondary to the effect of isoproterenol on other endocrine glands or the cardiovascular system.