Xi‐Qin Ding

Circulating pancreastatin is a marker for the enterochromaffin-like cells of the rat stomach

BACKGROUND/AIMS Peptides of the chromogranin family occur in peptide hormone-producing cells throughout the body. One source of such peptides is the enterochromaffin-like (ECL) cells, which constitute the predominant population of endocrine cells in the fundus (the acid-producing part) of the rat stomach. The purpose of this study was to examine whether ECL cells, which are controlled by gastrin, represent a major source of circulating pancreastatin, a fragment of chromogranin A. METHODS Rats underwent surgical procedures and treatments in which the ECL cells could be manipulated. The procedures included antrectomy, fundectomy, and gastrectomy (and adrenalectomy), and the treatments included fasting or feeding, gastrin-17 infusion, and administration of omeprazole or ranitidine. The concentrations of pancreastatin-like immunoreactivity (LI) and gastrin in the serum were determined by radioimmunoassay. RESULTS The serum pancreastatin-LI concentration was lowered by about 80% by fundectomy and gastrectomy; both of these procedures eliminated the ECL cell population. Adrenalectomy had no effect on the serum pancreastatin-LI concentration. Gastrin infusion, which activates the ECL cells, promptly increased serum pancreastatin-LI concentration. Refeeding after fasting and administration of omeprazole or ranitidine increased the serum pancreastatin-LI concentrations; these responses were prevented by antrectomy. CONCLUSIONS The concentration of circulating pancreastatin-LI reflects the activity of the ECL cells and the size of the ECL cell population in the rat stomach.

CCK2 receptor antagonists: pharmacological tools to study the gastrin–ECL cell-parietal cell axis

Gastrin-recognizing CCK2 receptors are expressed in parietal cells and in so-called ECL cells in the acid-producing part of the stomach. ECL cells are endocrine/paracrine cells that produce and store histamine and chromogranin A (CGA)-derived peptides, such as pancreastatin. The ECL cells are the principal cellular transducer of the gastrin-acid signal. Activation of the CCK2 receptor results in mobilization of histamine (and pancreastatin) from the ECL cells with consequent activation of the parietal cell histamine H2 receptor. Thus, release of ECL-cell histamine is a key event in the process of gastrin-stimulated acid secretion. The oxyntic mucosal histidine decarboxylase (HDC) activity and the serum pancreastatin concentration are useful markers for the activity of the gastrin-ECL cell axis. Powerful and selective CCK2 receptor antagonits have been developed from a series of benzodiazepine compounds. These agents are useful tools to study how gastrin controls the ECL cells. Conversely, the close control of ECL cells by gastrin makes the gastrin-ECL cell axis well suited for evaluating the antagonistic potential of CCK2 receptor antagonists with the ECL-cell HDC activity as a notably sensitive and reliable parameter. The CCK2 receptor antagonists YF476, YM022, RP73870, JB93182 and AG041R were found to cause prompt inhibition of ECL-cell histamine and pancreastatin secretion and synthesis. The circulating pancreastatin concentration is raised, was lowered when the action of gastrin on the ECL cells was blocked by the CCK2 receptor antagonists. These effects were associated with inhibition of gastrin-stimulated acid secretion. In addition, sustained receptor blockade was manifested in permanently decreased oxyntic mucosal HDC activity, histamine concentration and HDC mRNA and CGA mRNA concentrations. CCK2 receptor blockade also induced hypergastrinemia, which probably reflects the impaired gastric acid secretion (no acid feedback inhibition of gastrin release). Upon withdrawal of the CCK2 receptor antagonists, their effects on the ECL cells were readily reversible. In conclusion, gastrin mobilizes histamine from the ECL cells, thereby provoking the parietal cells to secrete acid. While CCK2 receptor blockade prevents gastrin from evoking acid secretion, it is without effect on basal and vagally stimulated acid secretion. We conclude that specific and potent CCK2 receptor antagonists represent powerful tools to explore the functional significance of the ECL cells.

Cholecystokinin-B receptor ligands of the dipeptoid series act as agonists on rat stomach histidine decarboxylase.

BACKGROUND & AIMS The effect of gastrin on the enterochromaffin-like cells in the rat stomach is mediated by cholecystokinin (CCK)-B receptors and manifested as activation of histidine decarboxylase (HDC). The dipeptoids PD 136450, PD 135158, and PD 134308 are thought to be selective CCK-B receptor antagonists. The effects of the dipeptoids and of gastrin-17 and sulfated CCK-8 on rat stomach HDC activity were examined. METHODS Drugs were infused intravenously or subcutaneously to fasted rats, and the HDC activity was determined. RESULTS The dipeptoids activated HDC with maximal responses (50%-60% of the maximal response to gastrin) at 1 mumol.kg-1.h-1. Rat gastrin-17 activated HDC maximally at 3 nmol.kg-1.h-1, and sulfated CCK-8 produced maximal response at 20 nmol.kg-1.h-1. The CCK-B receptor antagonist L-365,260 inhibited the HDC activation induced by gastrin, sulfated CCK-8, or the dipeptoids. The dipeptoids did not inhibit the gastrin-induced HDC activation. CONCLUSIONS Gastrin, sulfated CCK-8, and the dipeptoids activated rat stomach HDC. L-365,260 but not devazepide inhibited the HDC activation. Thus, the dipeptoids, which failed to inhibit the gastrin-induced HDC activation, act as CCK-B receptor agonists and not as antagonists. It is important to recognize this to ensure appropriate interpretation of data obtained with these drugs.

Long‐lasting cholecystokinin2 receptor blockade after a single subcutaneous injection of YF476 or YM022

Histamine‐forming ECL cells in the rat stomach operate under the control of gastrin. They represent a convenient target for studying cholecystokinin‐B/gastrin (CCK2) receptor antagonists in vivo. We examined the effectiveness and duration of action of two CCK2 antagonists, YM022 and YF476, with respect to their effect on ECL‐cell histidine decarboxylase (HDC) activity in the rat. Oral administration of subcutaneous deposition of YF476 or YM022 reduced the HDC activity. The maximum/near‐maximum dose for both drugs and for both modes of administration was 300 μmol kg−1 (effects measured 24 h after dose). At this dose and time the serum concentration of YF476 was 20–40 nmol l−1. The dose 300 μmol kg−1 was used in all subsequent studies. A single subcutaneous injection of YF476 inhibited the HDC activity for 8 weeks. The circulating concentration of YF476 remained high for the same period of time (15 nmol l−1). Subcutaneous YM022 suppressed the HDC activity for 4 weeks. A single oral dose of YF476 or YM022 inhibited the HDC activity for 2–3 days. Chronic gastric fistula rats were used to study the effect of subcutaneous YF476 on gastrin‐stimulated acid secretion. A single injection of YF476 prevented gastrin from causing an acid response for at least 4 weeks (the longest time studied). We conclude that a single subcutaneous injection of 300 μmol kg−1 YF476 causes blockade of CCK2 receptors in the stomach of the rat for 8 weeks thus providing a convenient method for studies of the consequences of long‐term CCK2 receptor inhibition.

Time‐course of deactivation of rat stomach ECL cells following cholecystokininB/gastrin receptor blockade

1 The so‐called enterochromaffin‐like (ECL) cells constitute 65–75% of the endocrine cells in the acid‐producing part of the rat stomach. They produce and secrete histamine and pancreastatin, a chromogranin A (CGA)‐derived peptide, in response to gastrin. Cholecystokinin (CCK)B/gastrin receptor blockade is known to suppress their activity. 2 We have examined the time course of the deactivation of the ECL cells following treatment with the selective CCKB receptor antagonists RP73870 and YM022. The drugs were given by continuous subcutaneous infusion for a time span of 1 h to 3 weeks and the serum gastrin concentration and various ECL cell parameters were measured (oxyntic mucosal histidine decarboxylase (HDC) activity, histamine and pancreastatin concentrations, HDC mRNA and CGA mRNA levels, and circulating pancreastatin concentration). 3 The two antagonists caused a prompt and dramatic decline in the oxyntic mucosal HDC activity and HDC mRNA level. The HDC activity started to decline after 1–2 h, was reduced by 60–70% after 6 h and was maximally suppressed (80–90%) after 24–48 h. The HDC mRNA level was reduced after 12 h and was at about 20% of the pretreatment level after 2–4 days of infusion. The ECL cell histamine concentration was lowered by about 50% after 7–10 days. 4 RP73870 and YM022 lowered the serum pancreastatin concentration and the oxyntic mucosal CGA mRNA level. The serum pancreastatin concentration was reduced by 40% after 6 h and the reduction was maximal after 2–3 days. A decline in the oxyntic mucosal CGA mRNA level was noted after 12 h with a maximal reduction after 2–4 days of infusion. The ECL cell pancreastatin concentration was reduced by 30–40% after 3 weeks. 5 The infusion of RP73870 and YM022 induced hypergastrinaemia. The serum gastrin concentration started to rise after 2–4 h, there was a 2 fold increase after 6 h and maximal increase (3–4 fold) after 2–3 days of treatment. 6 In conclusion, CCKB/gastrin receptor blockade promptly deactivates the ECL cells. Deactivation, manifested in a greatly reduced HDC activity, was apparent after 1–2 h of the infusion. The serum pancreastatin concentration and the oxyntic mucosal HDC mRNA and CGA mRNA levels were greatly reduced after 1–2 days. The ECL cell concentrations of histamine and pancreastatin declined quite slowly by comparison.

Reversibility of cholecystokinin-B/gastrin receptor blockade: A study of the gastrin-ECL cells axis in the rat

Gastrin acts via cholecystokinin-B/gastrin receptors to control histamine- and chromogranin A-producing ECL cells, which constitute the quantitatively predominant endocrine cell population in the acid-producing part of the rat stomach. Cholecystokinin-B receptor blockade is known to suppress the activity of ECL cells and to prevent their ability to respond to gastrin stimulation. The present study examines the reversibility of long-standing cholecystokinin-B receptor blockade of ECL cells. YM022, a potent and selective cholecystokinin-B receptor antagonist, was administered in a maximally effective dose by continuous subcutaneous infusion for 4 weeks (via osmotic minipumps). The resulting receptor blockade was manifested in elevated serum gastrin concentration (due to the ensuing acid inhibition), while the serum pancreastatin concentration, oxyntic mucosal histidine decarboxylase activity, histidine decarboxylase- and chromogranin A- mRNA levels and histamine and pancreastatin concentrations were lowered. After withdrawal of YM022, all these parameters returned to normal after varying lengths of time. The serum gastrin concentration and the oxyntic mucosal histidine decarboxylase activity returned to normal within a week after termination of treatment. The serum pancreastatin concentration and the mucosal histidine decarboxylase- and chromogranin A-mRNA levels returned to normal within 2 weeks of drug withdrawal. The mucosal pancreastatin and histamine concentrations remained unchanged for about a week before gradually returning to control levels within the next two weeks. Hence, the various effects of cholecystokinin-B receptor blockade of the ECL cells are fully reversible within 1-3 weeks of drug withdrawal.