The direct inhibition of pancreatic electrolyte secretion by noradrenaline in the isolated perfused cat pancreas

Altered glucose homeostasis in alpha2A-adrenoceptor knockout mice

To elucidate the functions of alpha2-adrenoceptor subtypes in metabolic regulation, we determined plasma glucose and insulin levels and tissue uptake of the glucose analogue 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) in C57Bl/6J wild-type (WT) and alpha2A-adrenoceptor knockout (alpha2A-KO) mice at baseline and following alpha2-adrenoceptor agonist ((+)-4-(S)-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole (dexmedetomidine)) and antagonist (4-[2-ethyl-2,3-dihydro-1H-inden-2-yl]-1H-imidazole (atipamezole)) administration. Basal glucose levels were 30% lower in alpha2A-KO mice than in WT mice. In WT mice, dexmedetomidine lowered insulin and elevated glucose levels, and atipamezole reduced glucose levels. In alpha2A-KO mice, neither drug affected the glucose or insulin levels. [18F]FDG uptake was investigated in plasma, heart, liver, kidney, pancreas, lung, fat, and skeletal muscle. Cardiac [18F]FDG uptake was a sensitive indicator of sympathetic function. Liver [18F]FDG uptake conformed to the plasma glucose levels. In alpha2A-KO mice, drug effects on [18F]FDG tissue uptake were absent. Thus, the alpha2A-adrenoceptor is the alpha2-adrenoceptor subtype primarily involved in the regulation of blood glucose homeostasis in vivo.

Catecholamines and 5-hydroxytryptamine in tissues of the rabbit exocrine pancreas

OBJECTIVES

Norepinephrine (NE), dopamine (DA), epinephrine (Epi), and 5-hydroxytryptamine (5-HT) all modulate pancreatic exocrine secretion, yet their concentrations in specific tissues of the exocrine pancreas are unknown.

METHODS

Concentrations of catecholamines and 5-HT in rabbit pancreatic ganglia, acini, ducts and ampullae, and arteries and veins were measured using HPLC.

RESULTS

Concentrations of NE in ganglia from the head/neck region were significantly higher than those from the body (1620 +/- 220 vs. 778 +/- 179 pmol/mg protein). Acini contained little NE, DA, or 5-HT (9 +/- 2, 0.9 +/- 0.2, 13 +/- 5 pmol/mg protein). Ducts and ampullae contained NE (314 +/- 74 and 156 +/- 24 pmol/mg protein), DA (43 +/- 14 and 13 +/- 4 pmol/mg protein), Epi (63 +/- 29 and 39 +/- 6 pmol/mg protein), and 5-HT (696 +/- 151 and 3563 +/- 288 pmol/mg protein). Arteries and veins contained the highest concentrations of NE (1962 +/- 463 and 736 +/- 80 pmol/mg protein, respectively).

CONCLUSIONS

Pancreatic ganglia and blood vessels, rather than acini, are the main sites of noradrenergic sympathetic innervation of the rabbit exocrine pancreas. These nerves preferentially target ganglionic transmission in the head/neck versus the body. Serotonergic nerves provide little or no innervation of rabbit pancreatic ganglia or acini.

Antro-pancreatic reflexes: long- and short-route reflexes in exocrine and endocrine pancreatic secretion in dogs

Pancreatic exocrine secretion is known to be facilitated by gastric antral distension via long- and short-route reflexes. In this study, we studied the effects of gastric distension on intra-pancreatic nerve discharges and blood insulin level as well as pancreatic exocrine secretion. Mongrel dogs were anesthetized with ketamine and thiopental, and immediately decerebrated. This study consisted of two series of experiments. In the first series, efferent discharges in an intra-pancreatic nerve branch were recorded, and its responses to antral distension were analyzed. In the second series, effects of antral distension on pancreatic exocrine secretion and blood insulin level were observed before and after vagotomy in splanchnicectomized dogs. Efferent discharges in a pancreatic nerve branch were increased by antral distension. Neither vagotomy nor splanchnicectomy produced obvious changes in the neural response. In splanchnicectomized dogs, antral distension elevated blood insulin level and increased pancreatic exocrine secretion. After subsequent vagotomy, these effects were reduced, but the increases were still greater than 50%. These results indicate that the antro-pancreatic short-route reflex plays a significant role in exocrine secretion, and also suggest that insulin release is increased by antral distension independent of blood glucose level.

Role of adrenergic receptors in veratridine-stimulated amylase secretion from rabbit pancreatic lobules

Sympathetic inhibition of pancreatic enzyme secretion has been attributed to vasoconstriction and direct inhibition of acinar cells. We observed both adrenergic inhibition and facilitation of cholinergic transmission in rabbit pancreatic ganglia, which innervate acini. Here we used pancreatic lobules to determine whether adrenergic receptors also regulate synaptic transmission between pancreatic nerves and acini. Stimulation of pancreatic nerve terminals with veratridine (Ver), an activator of voltage-dependent Na+ channels, resulted in a 102% increase in amylase secretion, which was unaffected by alpha and beta receptor antagonists but inhibited 65% by atropine. At a concentration of 10 microM, norepinephrine inhibited (38%) and epinephrine potentiated (40%) Ver-stimulated secretion. At the same concentration, the alpha2 agonist clonidine (Clon) inhibited (39%), whereas the nonselective beta agonist isoproterenol (Iso) and the selective beta3 agonist BRL 37344 potentiated (71 and 67%, respectively) nerve-stimulated secretion. The effects of Clon and Iso and BRL 37344 were antagonized by yohimbine and propranolol, respectively. Phenylephrine, dobutamine, and terbutaline had no effect. Neither basal, bethanechol-stimulated, nor noncholinergic nerve-stimulated secretion was significantly altered by Clon or Iso. Thus, cholinergic nerve terminals innervating pancreatic acini exhibit both inhibitory alpha2 and atypical facilitatory beta adrenergic receptors. The apparent lack of adrenergic innervation suggests that adrenergic receptors on the nerve terminals of cholinergic pancreatic neurons are under hormonal control by circulating catecholamines. These results provide further evidence that intrinsic pancreatic neurons, which supply most, if not all, of the cholinergic innervation of acini, are important sites of sympathetic regulation of pancreatic exocrine secretion.

Arginine vasopressin inhibits fluid secretion in guinea pig pancreatic duct cells

The effects of arginine vasopressin (AVP) on pancreatic ductal secretion were studied in guinea pigs. In the isolated vascularly perfused pancreas, AVP reduced secretin-stimulated fluid secretion and increased the vascular resistance when the perfusion rate was held constant. In the isolated interlobular duct segments, AVP inhibited secretin-stimulated fluid secretion, indicating the direct inhibitory action of AVP on the duct cells. AVP affected neither the basal nor the secretin-induced cAMP productions, suggesting that AVP inhibits the fluid secretion at a point distal to the production of cAMP. AVP increased intracellular Ca(2+) concentration ([Ca(2+)](i)) in the absence of extracellular Ca(2+). When [Ca(2+)](i) was elevated by the application of thapsigargin, AVP caused a rapid decrease in [Ca(2+)](i). AVP seems to activate both Ca(2+) release from intracellular stores and Ca(2+) efflux across the plasma membrane, but its relation to the inhibition of fluid secretion remains to be clarified. It is concluded that AVP directly inhibits secretin-stimulated ductal fluid secretion in the guinea pig pancreas.

Adenylate cyclase activity in human pancreatic adenocarcinoma cell lines

CONCLUSION

BxPC-3, Hs 766T, Capan-2, Panc-1, and Capan-1 cells possess receptors for VIP and beta-adrenergic agonists that are functionally coupled to adenylate cyclase. In this respect, they resemble pancreatic duct cells. However, we speculate that the process of neoplastic transformation has either downregulated the expression of secretin receptors or led to a defect in the receptor itself, placing a question mark over the usefulness of these adenocarcinoma cell lines as models of the pancreatic ductal epithelium

BACKGROUND

Because of the importance of ducts in pancreatic disease, we wished to establish which duct cells receptors are functional on adenocarcinoma cell lines.

METHODS

We investigated the expression of agonist-stimulated adenylate cyclase activity in six human pancreatic adenocarcinoma cell lines. Known stimulants of pancreatic ductal secretion, VIP, PHI, secretin, beta-adrenergic, and dopamine, were tested.

RESULTS

For responsive cell lines, VIP was the most effective stimulant followed by adrenaline, isoprenaline, PHI, and secretin. Dopamine was without effect. Since high concentrations of PHI and secretin were required to stimulate cyclase activity, their effect is probably mediated by VIP receptors. Based on the degree of stimulation observed with the individual agonist, Hs 766T and BxPC-3 were the most responsive cell lines, followed by Capan-2 and Capan-1, and finally Panc-1. MIAPaCa-2 cells did not respond to any of the agonists tested.

Cholinergic and adrenergic control of enzyme secretion in isolated rat pancreas

While cholinergic nervous control of pancreatic enzyme secretion is well documented, data concerning adrenergic regulation of the exocrine pancreas are contradictory. In the present study we attempted to elucidate the direct action of adrenergic stimulation on pancreatic enzyme secretion. Rat pancreatic segments were set up in an organ bath and superfused with modified Krebs-Henseleit solution. Electrical field stimulation (EFS) stimulated amylase release from the segments. This stimulation was subject to inhibition with atropine up to 80%. Atropine-resistant enzyme discharge in response to EFS could be blocked by propranolol. Cholinergic agonist urecholine-induced amylase release was completely blocked by atropine. Noradrenaline (NA) exhibited a biphasic effect on amylase release. It inhibited the urecholine-induced amylase release in lower concentrations (10(-8)-10(-7) M), while it stimulated basal enzyme secretion in higher concentrations (10(-5)-10(-4) M). The inhibitory effect was mimicked by phenylephrine and completely prevented by prazosin. Isoprenaline concentration dependently enhanced, while clonidine and guanfacine did not affect amylase discharge. In conclusion, in rat pancreatic acinar tissue it seems likely that acetylcholine is the main neurotransmitter. Adrenergic action can be dual, inhibitory via alpha 1-adrenoceptors or stimulatory via beta-adrenoceptors on amylase secretion.

A mixed endocrine adrenal tumour causing steatorrhoea

A 60 year old man developed steatorrhoea, weight loss, mild diabetes mellitus, labile hypertension and limb cramps. Raised plasma concentrations of catecholamines, particularly noradrenaline and a computed tomography-scan showing an adrenal tumour strongly suggested a pheochromocytoma. Adrenoreceptor blockade reversed the symptoms, decreased faecal fat, and increased duodenal trypsin to normal concentrations. After adrenalectomy the patient was asymptomatic and there was no steatorrhoea. The blood glucose concentrations became normal. Immunocytochemistry revealed the tumour cells to store large amounts of enkephalin and somatostatin reactive material and moderate amounts of immunoreactive beta-endorphin and dynorphin.

Dopamine, noradrenaline and isoprenaline: secretory and electrophysiological effects in vitro on mouse pancreas

The amylase release from mouse pancreatic fragments was studied after dopamine (DA), and alpha- or beta-sympathomimetic agonist application. The electrical parameters of the acinar cell membrane were also monitored. Both DA (from 5 X 10(-6) to 10(-4) M) and beta-stimulants (isoprenaline from 5 X 10(-6) to 5 X 10(-5) M; noradrenaline from 3 X 10(-4) to 10(-3) M) evoked an increase in amylase release, while noradrenaline in alpha-receptor stimulating doses failed to have any effect. The stimulatory effect of DA was blocked by ganglion blockers (Arfonad 10(-5) M; pentamethonium 3 X 10(-5) M) in a competitive manner and a dual antagonism was observed with atropine (10(-7) M, 10(-9) M). An alpha-receptor antagonist (phentolamine 10(-5) M) and a beta-receptor antagonist (propranolol 10(-5) M) had no influence on the dopamine response. Moreover, the DA-induced stimulation was dependent on the presence of extracellular calcium. Perfusion with 10(-4) and 10(-3) M-DA or local application (from 77 micrograms to 4.3 mg), resulted in marked membrane depolarization with diminution of the input resistance. This effect was blocked by atropine (10(-5) M) and pentamethonium (10(-4) M), but not by propranolol (10(-5) M) or phentolamine (10(-5) M). The isoprenaline- (IP) and noradrenaline- (NA) induced increase in amylase release was competitively blocked by propranolol (10(-5) M) but not by phentolamine (10(-5) M). Atropine caused a dose-dependent (10(-7) M, 10(-6) M) decrease in the maximal response (non-competitive antagonism), while the ganglion blocker pentamethonium (10(-4) M) was without effect. NA caused membrane depolarization accompanied by a decrease in the input resistance after local application (from 77 micrograms to 1.6 mg). This effect persisted in the presence of 10(-5) M-phentolamine but was abolished by 10(-5) M-propranolol. IP perfusion (10(-4) and 10(-3) M) or local application (0.3 M; from 32 to 130 micrograms) caused the same electrical changes as those induced by NA and DA. The effect of IP persisted in the presence of 10(-5) M-phentolamine, 10(-4) M-pentamethonium and 10(-4) M-domperidone, but was abolished by propranolol (10(-5) M) and tetrodotoxin (5 X 10(-6) M) and markedly diminished by atropine (10(-5) M).(ABSTRACT TRUNCATED AT 400 WORDS)

Ex-vivo isolated perfusion of the pancreas in the Syrian golden hamster

The technique of ex-vivo isolated pancreatic perfusion has been a valuable method for investigation of the physiology of the exocrine and endocrine pancreas. We have adapted the technique of isolated pancreatic perfusion for use in the Syrian golden hamster, an animal used widely in studies of pancreatic carcinogenesis. The technique involves surgical harvest of the pancreas with its aortic and portal venous blood supply intact and perfusion of the pancreas with a modified Krebs buffer at 37 degrees C. Physiological function of the perfused pancreas system was examined in 27 Syrian hamsters. In tests of endocrine function, the perfused pancreas responded by increasing insulin secretion within 1 min of elevating perfusate glucose concentration, and also secreted insulin promptly in response to 10 mM arginine. In exocrine studies, the flow of pancreatic juice was stimulated by the addition of 0.8 X 10(-9) M secretin to the perfusate, and amylase output was significantly increased by the addition of 0.2 X 10(-9) M cholecystokinin (CCK-8). The ex-vivo isolated perfused pancreas in the hamster thus appears to respond appropriately to physiological stimuli and is a valuable additional tool for studies of the hamster pancreas.