Giorgio Linari

The action of caerulein on pancreatic and biliary secretions of the chicken

Abstract Caerulein, by intravenous infusion, had a strong stimulating action on the chickens pancreatic secretion. Threshold rates were 0.1–0.25 ng/kg/min. Subcutaneous injection proved ineffective up to 5 mug/kg; by rapid intravenous injection the action was manifest only with 50 ng/kg. Caerulein increased output of fluid, bicarbonate and enzymes, greatly enhancing the enzyme concentration. Atropine inhibited the effect of caerulein on enzyme concentration only. Porcine secretin had no effect on the chickens pancreatic secretion. Flow of hepatic bile and the output of solid biliary components were also stimulated by caerulein. The threshold doses were: 10 ng/kg by rapid intravenous injection, and 0.5 ng/kg/min by intravenous infusion. These actions were not inhibited by atropine. Caerulein hastened plasma clearance and biliary excretion of BSP. Furthermore, it increased output of cystic bile by stimulating gall bladder motility. Tachyphylaxis to effects of caerulein on pancreastic or biliary secretions was not seen. Porcine secretin reduced the flow of hepatic bile by intravenous infusion. The mechanism of action of caerulein is discussed.

The effects of [Arg14, Lys15] nociceptin/orphanin FQ, a highly potent agonist of the NOP receptor, on in vitro and in vivo gastrointestinal functions

Nociceptin/orphanin FQ (N/OFQ) administered into the lateral left cerebral ventricle of rats has been reported to inhibit in vivo gut motor and secretory functions. Recently, a novel N/OFQ analog, [Arg14, Lys15] N/OFQ, was synthesized and demonstrated to behave as a highly potent agonist at the human recombinant N/OFQ peptide (NOP) receptors and to produce long-lasting effects in vivo in mice compared with the natural ligand N/OFQ. In the present study, the pharmacological profile of [Arg14, Lys15] N/OFQ was further evaluated and compared with that of N/OFQ in vitro on guinea pig exocrine pancreas and in vivo on gastric emptying, colonic propulsion and gastric acid secretion in rats. [Arg14, Lys15] N/OFQ and N/OFQ significantly decreased the KCl-evoked amylase secretion from isolated pancreatic lobules of the guinea pig. In in vivo experiments, [Arg14, Lys15] N/OFQ mimicked the effects of N/OFQ, inducing, after intracerebroventricular injection, a delay (up to 70%) in the gastric emptying of a phenol red meal, an increase (about 40 times) of the mean bead colonic expulsion time and a decrease (up to 90%) of gastric acid secretion in water loaded rats after 90 min pylorus ligature. In all these assays, [Arg14, Lys15] N/OFQ was more effective than N/OFQ, and its effective doses were at least 10-fold lower than N/OFQ effective doses. The highly selective NOP receptor antagonist, UFP-101, decreased the efficacy of [Arg14, Lys15] N/OFQ in in vitro and in vivo assays above reported. These findings: (a) show that pancreatic NOP receptors mediate an in vitro inhibitory effect on stimulated guinea pig amylase secretion; (b) confirm that the stimulation of central NOP receptors exerts an inhibitory control on gastric emptying, colonic motility and gastric secretion in rats and (c) put in evidence that [Arg14, Lys15] N/OFQ, being more potent and effective than the natural ligand N/OFQ, represents a new pharmacological tool for the study of the physiological and pharmacological roles mediated by the N/OFQ-NOP receptor system.

Involvement of cannabinoid CB1- and CB2-receptors in the modulation of exocrine pancreatic secretion.

The role of the cannabinoid system in the regulation of exocrine pancreatic secretion was investigated by studying the effects of the synthetic CB1- and CB2-receptors agonist, WIN55,212, on amylase secretion in isolated lobules and acini of guinea pig and rat, and the expression of CB-receptors in rat pancreatic tissue by immuno-chemistry and Western-blot analysis in both basal and cerulein (CK)-induced pancreatitis condition. In pancreatic lobules of guinea pig and rat, WIN55,212 significantly inhibited amylase release stimulated by KCl depolarization through inhibition of presynaptic acetylcholine release, but did not modify basal, carbachol- or CK-stimulated amylase secretion. The effect of WIN55,212 was significantly reduced by pre-treatment with selective CB1- and CB2-receptor antagonists. The antagonists, when given alone, did not affect the KCl-evoked response. Conversely, WIN55,212 was unable to affect basal and CK- or carbachol-stimulated amylase release from pancreatic acini of guinea pig and rat. Immunofluorescent staining of rat pancreatic tissues showed that CB1- and CB2-receptors are expressed in lobules and in acinar cells and their presence in acinar cells was also shown by Western-blot analysis. After CK-induced pancreatitis, the expression of CB1-receptors in acinar cells was not changed, whilst a down-regulation of CB2-receptors was observed. In conclusion, the present study shows that WIN55,212 inhibits amylase release from guinea pig and rat pancreatic lobules and, for the first time, that cannabinoid receptors are expressed in lobules of the rat pancreas, suggesting an inhibitory presynaptic role of this receptor system. Finally, in rat pancreatic acinar cells, CB1- and CB2-receptors, expressed both in basal conditions and after CK-induced pancreatitis but inactive on amylase secretion, have an unknown role both in physiological and pathological conditions.

The action of caerulein on gastric secretion of the chicken.

Abstract Caerulein stimulated gastric secretion of the chicken, particularly after intravenous infusion. The threshold doses given by subcutaneous and intravenous injection were 10 ng/kg and 50 ng/kg respectively. Caerulein increased output of the fluid and solid components of gastric juice and generally raised the concentration of pepsin. Slight tachyphylaxis particularly on the fluid and acid components was observed. Caerulein stimulation of gastric secretion was completely inhibited by atropine but unaffected by drugs altering histamine stores. Caerulein was four time as effective on fluid and acid secretion than human gastrin I, and fifteen times as effective on pepsin secretion. Porcine secretin did not affect the chickens gastric secretion.

Effect of bombesin on pancreatic secretion and gall bladder motility of the chicken

Bombesin strongly stimulated the chicken pancreatic secretion. When given by i.v. infusion, the threshold dose was of the order of 7.5-45.0 ng/kg/min and maximum enzyme output was obtained at a rate of 60 ng/kg/min. In addition to total enzyme output, enzyme concentration was also increased. Caerulein displayed a more potent stimulant effect, but composition of juice produced by the two polypeptides was similar. Tachyphylaxis occurred only with bombesin. Neither atropine nor gastric acidification affected the response to bombesin. Bombesin was totally ineffective in promoting gall bladder emptying. It is suggested that in the chicken, bombesin acts on the exocrine pancreas indirectly through release of an endogenous pancreozymin possibly devoid of cholecystokinetic activity.

Cannabinoid agonist WIN55,212 in vitro inhibits interleukin‐6 (IL‐6) and monocyte chemo‐attractant protein‐1 (MCP‐1) release by rat pancreatic acini and in vivo induces dual effects on the course of acute pancreatitis

Background  Cannabinoids (CBs) evoke their effects by activating the cannabinoid receptor subtypes CB1‐r and CB2‐r and exert anti‐inflammatory effects altering chemokine and cytokine expression. Various cytokines and chemokines are produced and released by rodent pancreatic acini in acute pancreatitis. Although CB1‐r and CB2‐r expressed in rat exocrine pancreatic acinar cells do not modulate digestive enzyme release, whether they modulate inflammatory mediators remains unclear. We investigated the CB‐r system role on exocrine pancreas in unstimulated conditions and during acute pancreatitis. Methods We evaluated in vitro and in vivo changes induced by WIN55,212 on the inflammatory variables amylasemia, pancreatic edema and morphology, and on acinar release and content of the cytokine interleukin‐6 (IL‐6) and chemokine monocyte chemo‐attractant protein‐1 (MCP‐1) in untreated rats and rats with caerulein (CK)‐induced pancreatitis. Key Results In the in vitro experiments, WIN55,212 (10−6 mol L−1) inhibited IL‐6 and MCP‐1 release from acinar cells of unstimulated rats and after CK‐induced pancreatitis. In vivo, when rats were pretreated with WIN55,212 (2 mg kg−1, intraperitoneally) before experimentally‐induced pancreatitis, serum amylase, pancreatic edema and IL‐6 and MCP‐1 acinar content diminished and pancreatic morphology improved. Conversely, when rats with experimentally‐induced pancreatitis were post‐treated with WIN55,212, pancreatitis worsened. Conclusions & Inferences These findings provide new evidence showing that the pancreatic CB1‐r/CB2‐r system modulates pro‐inflammatory factor levels in rat exocrine pancreatic acinar cells. The dual, time‐dependent WIN55,212‐induced changes in the development and course of acute pancreatitis support the idea that the role of the endogenous CB receptor system differs according to the local inflammatory status.

Selective tachykinin NK3-receptor agonists stimulate in vitro exocrine pancreatic secretion in the guinea pig

The tachykinins, including substance P, neurokinin A and neurokinin B, are a mammalian peptide family that have documented motor, sensory and circulatory neurotransmitter functions in the gut. Little is known about their action on the exocrine pancreas. In this study we investigated the effects of PG-KII, a natural NK3-tachykinin receptor agonist, and senktide, a synthetic NK3-tachykinin receptor agonist, on amylase release from isolated pancreatic lobules of the guinea pig in comparison with the secretagogues carbachol, caerulein and substance P and the depolarizing agent KCl. When added to incubation flasks at various concentrations (from 10(-10) to 10(-6)M), PG-KII and senktide both caused a dose-dependent increase in amylase release from pancreatic lobules. PG-KII and senktide elicited a lower maximal response (7.5+/-0.8 and 8.1+/-0.6% of the total lobular amylase content) than carbachol (34.4+/-3.9%), caerulein (26.5+/-2.8%) and KCl (22.5+/-3.8%). Whereas atropine left PG-KII and senktide-stimulated secretion unaffected, the non peptide NK3 receptor antagonist SR 142801 significantly reduced the stimulant effect of PG-KII and senktide. PG-KII (10(-7)M) also slightly though significantly increased the response to lower concentrations of caerulein (10(-11) and 10(-10)M) and carbachol (10(-7) and 10(-6)M). These findings show that PG-KII and senktide are weak stimulants of exocrine pancreatic secretion that act directly on the acinar cells through NK3 receptors, without cholinergic involvement. We suggest also that the tachykininergic NK3 receptor system cooperates with the other known secretagogues in the control of pancreatic exocrine secretion.

The action of bombesin on gastric secretion of the chicken

The natural tetradecapeptide bombesin at a threshold dose of 3--5 ng/kg/min i.v. stimulates gastric secretion in the chicken with either an acute or a chronic proventriculus fistula; this effect is blocked by atropine. The occurrence of tachyphylaxis in the acute, but not in the chronic preparation, and the inhibition of the response by proventriculus acidification, in the presence of an intact sensitivity to caerulein -- a directly stimulating agent -- support the hypothesis of an indirect mechanism of action of bombesin, namely the release of endogenous gastrin, as well as of the existence of gastrin also in the chicken.

Stimulatory effect of PG-KII, an NK3 tachykinin receptor agonist, on isolated pancreatic acini: species-related differences

More information is needed on the physiological role of the tachykinins (TKs), especially neurokinin3-receptor (NK3) agonists, in the pancreas. In this paper we investigated and compared the effect of PG-KII (10(-9) to 10(-6) M), a natural NK3-receptor agonist, with that of the known secretagogues substance P (10(-9) to 10(-6)M), caerulein (10(-11) to 10(-8) M) and carbachol (10(-8) to 10(-5) M), on amylase secretion from dispersed pancreatic acini of the guinea pig and rat. PG-KII (10(-7) M) significantly increased basal amylase release from guinea pig pancreatic acini (from 5.4+/-0.9% to 11.3+/-0.5%, P < 0.05) but left basal release in the rat unchanged (6.5+/-0.5%). The stimulant effect of PG-KII on guinea pig acini was significantly reduced by the NK3-receptor antagonist, SR 142801 (5 x 10(-7) M), and left unchanged by the NK1-receptor antagonist, SR 140333 (5 x 10(-7) M). Conversely, substance P (10(-7) M) significantly stimulated amylase secretion from rat and guinea pig acini (12.6+/-0.6% and 12.1+/-0.7%, P < 0.05). This stimulated effect of substance P was antagonized by the NK1--receptor antagonist (5 x 10(-7) M), but not by the NK3-receptor antagonist (5 x 10(-7) M). The PG-KII- and substance P-evoked maximal responses were lower than those evoked by caerulein (10(-9) M) (guinea pig, 19.1+/-1.3%; rat, 1802+/-0.9%, P < 0.01) and carbachol (10(-5) M) (guinea pig, 23.3+/-1.2%; rat, 24.0+/-1.1%, P < 0.01). The inhibitors of phospholipase C U-73122 (10(-5) M), phospholipase A2 quinacrine (10(-5)M), and protein tyrosine kinase genistein (10(-4) M), partly but significantly inhibited PG-KII, as well as carbachol-stimulated amylase release. Coincubation of PG-KII 10(-7) M with submaximal doses of caerulein (10(-11) to 10(-10) M) and carbachol (10(-7) to 10(-6) M) had an additive effect on amylase release. Pre-incubation with PG-KII (10(-7) M) for 30 min significantly reduced the subsequent amylase response to PG-KII, whereas pre-incubation with caerulein 10(-10) M or carbachol 10(-6) M did not. These findings suggest that PG-KII directly contributes to pancreatic exocrine secretion by interacting with acinar NK3 receptors of the guinea pig but not of the rat. PG-KII signal transduction involves the intracellular phospholipase C, phospholipase A2 and protein tyrosine kinase pathways. The NK3 receptor system cooperates with the other known secretagogues in regulating guinea pig exocrine pancreatic secretion and undergoes rapid homologous desensitization.

Features of the choleretic action of caerulein

Abstract I.v. infusion of caerulein had a thorough choleretic effect in the chicken, stimulating secretion of bicarbonate and bile salts, both in the absence of enterohepatic circulation of bile salts, and in animals in which bile secretion was supported with i.v. or intraduodenal administration of exogenous bile salts. In the case of the intraduodenal route, both the concentration and output of bile salts were increased. A dose-response relation was evident, although more modest in the case of the bile salts output than in the bicarbonate output. A significant positive correlation between bile salts output and bile flow during caerulein stimulation was evident. The mechanism of the choleretic action of caerulein in the presence or absence of an enterohepatic circulation of bile salts is discussed.