The effect of adrenaline and noradrenaline on the blood flow, electrical conductance and external secretion of the pancreas

The influence of the splanchnic nerves on the external secretion, blood flow and electrical conductance of the cat pancreas

1. Electrical stimulation of the cut peripheral end of the splanchnic nerves results in a biphasic change in electrical conductance measured across the tail of the pancreas. A phase of decreased conductance is followed by a more prolonged phase of increased conductance.2. Simultaneous measurements of pancreatic blood flow indicate that the phase of decreased conductance occurs as a result of vasoconstriction, whilst the phase of increased conductance is due to vasodilatation.3. The initial phase of decreased conductance and vasoconstriction is abolished by alpha-receptor blocking agents such as phenoxybenzamine and the phase of increased conductance blocked by beta-receptor blocking agents such as pronethalol.4. Short periods of electrical stimulation applied to the splanchnic nerves result in a secretion of amylase and a reduction in the volume rate of secretion.5. When the vasoconstrictor response was abolished by phenoxybenzamine, nerve stimulation still reduced the rate of secretion, suggesting that the inhibitory effect is in part due to a direct action of the secretory cells.6. After bretylium tosylate, splanchnic nerve stimulation no longer produced vasomotor changes in the pancreas and the inhibitory effect on the volume response was converted to one of augmentation, but the secretion of enzymes was unaffected.7. The secretion of amylase on splanchnic stimulation was abolished by intravenous injection of atropine, suggesting that a cholinergic mechanism is involved.8. Noradrenaline did not mobilize pancreatic enzymes.

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.

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.

Noradrenergic inhibition of canine gallbladder contraction and murine pancreatic secretion during stress by corticotropin-releasing factor

Gastrointestinal secretory and motor responses are profoundly altered during stress; but the effects of stress and its mediator(s) on the two major gut functions, exocrine pancreatic secretion and gallbladder motility, are unknown. We therefore developed two animal models that allowed us to examine the effects of acoustic stress on canine gallbladder contraction and restraint stress on rat exocrine pancreatic secretion. Acoustic stress inhibited cholecystokinin-8 (CCK)- and meal-induced gallbladder contraction, and restraint stress inhibited basal and CCK/secretin-stimulated pancreatic secretion. These inhibitory responses were mimicked by cerebral injection of corticotropin-releasing factor (CRF) and abolished by the CRF antagonist, alpha-helical CRF-(9-41). The effects of stress and exogenous CRF were simulated by intravenous infusion of norepinephrine but prevented by ganglionic, noradrenergic, and alpha-adrenergic but not beta-adrenergic receptor blockade. Vagotomy, adrenalectomy, and--in rats--hypophysectomy did not alter the effects produced by stress and CRF. These results indicate that endogenous CRF released in response to different stressors in distinct species inhibits canine gallbladder contraction and murine exocrine pancreatic secretion via activation of sympathetic efferents. Release of norepinephrine appears to be the final common pathway producing inhibition of biliary and pancreatic digestive function during stress mediated by cerebral CRF.

Regulation of rat ileal water absorption by central alpha 2 adrenergic receptors

This study examined the role of central adrenergic receptors in the regulation of water absorption by the rat ileum. Clonidine, an alpha 2-adrenergic receptor agonist, increased water absorption in vivo following intracerebroventricular but not intravenous injection. Intracerebroventricular injection of prazosin, an alpha 1-adrenergic receptor antagonist, did not alter basal water absorption. Prazosin did not prevent the clonidine effect. In contrast, the alpha 2-adrenergic receptor antagonist, yohimbine, reduced basal absorption and prevented the intracerebroventricular clonidine effect. Treatment with reserpine reduced ileal norepinephrine content by 98%, reduced basal water absorption consistent with a loss of sympathetic outflow to the mucosa, but did not prevent the increase in water absorption due to intracerebroventricular clonidine. These results suggest that central alpha 2 receptors regulate water absorption by the rat ileum. The clonidine-induced increase in water absorption is not mediated by the sympathetic nerves innervating the intestine.

Alpha-adrenergic influences on exocrine pancreatic secretion in the rabbit

Action of phenylephrine (35 micrograms/Kg/min) alone or previously blocked by phentolamine (100 micrograms/Kg/min) on exocrine pancreatic secretion of anaesthetized rabbits has been studied, in basal state or under stimulation by secretin (1 C.U./Kg/h) or by the octapeptide of cholecystokinin (OP-CCK) (0.15 Ivy dog units/Kg/h). Phenylephrine increased arterial pressure. This effect was blocked by phentolamine. However no variations were seen in pancreatic blood flow in any of the experimental conditions assayed. Phenylephrine produced a secretin-like effect on hydroelectrolytic secretion in basal conditions. This action was maintained after the infusion of secretin but not after OP-CCK. This effect was not blocked by phentolamine. Phenylephrine increased protein secretion in the basal state, an action that was blocked by phentolamine. After secretin or OP-CCK stimulation phenylephrine did not increase protein secretion. It is concluded that phentolamine blocks the effects of phenylephrine on acinar cells but not on ductular cells.

The influence of cutting the pancreatic nerve plexus on exocrine function in the pancreas of rats

This study was performed to clarify changes in protein synthesis and exocrine enzymes of the pancreas after cutting the pancreatic nerve plexus of Wistar rats. The rats were divided into two groups, consisting of a group that underwent cutting of the pancreatic nerve plexus (neurotomy group) and a group that underwent a sham operation (control group). 3H-leucine uptake in the pancreatic protein fraction of the neurotomy group at 3, 5 and 7 days after the operation was significantly lower than that of the control group (P less than 0.05-0.01), and this low uptake returned to the normal range at 14 days. Amylase, lipase and trypsin values in pancreatic tissue of the neurotomy group decreased during the period of from 1 to 7 days, and there were significant differences in the values of the respective enzymes at 5 or 7 days between the neurotomy and the control group (P less than 0.05). Thereafter, all enzyme values increased to within the normal range. Upon examination of pancreatic blood flow using a microsphere, the neurotomy group showed a significant reduction at 7 days compared with the control group (P less than 0.05), and thereafter exhibited recovery of blood flow. These results indicate that after cutting the pancreatic nerve plexus, exocrine function in the pancreas is reduced immediately but recovers within a short period of time, and that these changes in exocrine function are affected by blood flow in the pancreas.

Beta 1 and beta 2 adrenergic agonists in exocrine pancreatic secretion in the rabbit

The effect of Dobutamine (a beta 1-adrenergic agonist) and Terbutaline (a beta 2-adrenergic agonist) on exocrine pancreatic secretion was studied in anaesthetized rabbits, simultaneously controlling pancreatic blood flow and blood pressure. The secretion of fluid and ions (bicarbonate, sodium and potassium) was unaffected by the infusion of Dobutamine (8 micrograms.kg-1.min-1) or Terbutaline (10 micrograms.kg-1.min-1). Neither were pancreatic blood flow or mean blood pressure altered. Dobutamine or Terbutaline depress the function of the acinar cells, amylase secretion being more affected by the action of Terbutaline. The results show that beta 1 and beta 2-adrenergic stimulation has no effect on the ductular cells but does decrease the secretion by the acinar cells.

Flow distribution between the endocrine and exocrine parts of the isolated rat pancreas during perfusion in vitro with different glucose concentrations

Previous studies in our laboratory have indicated that pancreatic islet blood flow is stimulated by glucose. In an attempt to evaluate to what extent intrapancreatic control mechanisms are involved in the glucose modulation of islet blood flow the distribution of flow between the endocrine and exocrine parts of the rat pancreas during perfusion in vitro with different glucose concentrations have now been studied. For this purpose pancreatic glands from 29 rats were perfused at a flow rate of 1.5 ml min-1 for 95 min with low (2.8 mM) or high (16.7 mM) glucose-containing media. Maintenance of vascular reactivity of this preparation in spite of a marked exocrine oedema was confirmed by administration to the perfusion medium of adrenaline, which immediately raised the perfusion pressure. Insulin concentrations in the effluent media were measured to correlate rates of insulin release to changes in islet flow and to assess the functional viability of the preparation. In each experiment non-radioactive microspheres with a diameter of 10 micron were injected into the perfusion medium at one of four time-points: 15, 30, 35 or 80 min after the beginning of the perfusion. Two of these injections (15 and 80 min) took place during perfusion with the low-glucose media and the remaining two during perfusion with high-glucose medium. The microspheres were counted separately in the endocrine and exocrine parts of the pancreas. The results showed that all preparations had a biphasic insulin response to glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Entero-pancreatic reflexes revealed by duodenal anesthesia in the dog

This study was designed to improve our understanding of duodeno-pancreatic reflexes, the existence of which was suggested by the previous observation of a reduction in secretin-stimulated pancreatic secretion during local anesthesia of the duodenal mucosa. The effects on this reduction in secretin-stimulated secretion of cholinergic or adrenergic blocking agents (alone or in combination) and of truncal vagotomy, were studied in conscious dog with gastric and pancreatic fistulae. For each agent and for secretin alone in normal and vagotomized dogs, a comparison was made of pancreatic secretion with and without lignocaine anesthesia of the duodenal mucosa. Lignocaine reduced pancreatic secretion with secretin alone, and stimulated it during infusion of atropine. The changes in both protein bicarbonate secretion were blocked by pentolinium and by phenoxybenzamine whereas propranolol mainly blocked the effects on bicarbonate output. The effect of truncal vagotomy resembled that of atropine. These results suggest the existence of two enteropancreatic reflex mechanisms; an excitory cholinergic vagal reflex and an inhibitory, atropine-resistant non-vagal reflex. Both are blocked by pentolinium (a ganglion blocker) and by phenoxy-benzamine, suggesting the involvement of alpha-adrenergic receptors probably also at the level of the ganglion cell. Beta-adrenergic receptors are also involved in the regulation of bicarbonate and fluid secretion.

Inhibition of pancreatic exocrine secretion and bile entry into the duodenum by isometheptene, a sympathomimetic agent

We have studied the effect of isometheptene, an indirectly acting sympathomimetic with analgesic and antispastic properties, on secretin-cholecystokinin-stimulated pancreatic and biliary outputs. Isometheptene, infused intravenously at a dose of 100 mg in 30 min, significantly inhibited bicarbonate, enzyme, and bilirubin output in eight healthy subjects (compared to control values, the maximum percent inhibition was 34% for bicarbonate, 57% for lipase, 61% for chymotrypsin, and 86% for bilirubin). In four cholecystectomized subjects, the drug inhibited only pancreatic outputs. The inhibitory effect on pancreatic secretion, coupled with the analgesic action, suggest a potential benefit of this drug in acute pancreatic pathology.

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

The continuous infusion of noradrenaline into the arterial supply of the isolated saline-perfused pancreas caused a dose-dependent rise in perfusion pressure, a reduction in perfusion rate and an inhibition of pancreatic secretion. With increasing dose there was always a greater reduction in secretion rate than there was of perfusate flow rate. Manual reduction of the perfusion rate resulted in a reduction in secretion rate. When noradrenaline reduced the perfusate flow by 44.2 +/- 6.0% the secretion rate fell by 76.6 +/- 14.1%. Manual reduction of the perfusion flow rate by a similar amount (43.0 +/- 5.7%) only reduced the secretion rate by 41.4 +/- 7.0%. The infusion of noradrenaline, when all calcium had been removed from the perfusate, caused only a small increase in perfusion pressure with little change in the perfusion flow whilst at the same time the inhibition of electrolyte secretion was relatively unaffected. The vasomotor and secretory effects of noradrenaline were abolished by phentolamine. It is concluded that noradrenaline inhibits pancreatic electrolyte secretion by a direct action on the secretory cell and indirectly by vasoconstriction and that both these effects are mediated through the alpha-receptor.

Effects of nicardipine on pancreatic exocrine secretion in the dog

1. The effects of nicardipine on the secretion of pancreatic juice were investigated in dog isolated, blood-perfused pancreas, and compared with those of papaverine, aminophylline and secretin. 2. Intra-arterial administration of nicardipine (1-10 micrograms) elicited a dose-dependent increase in pancreatic secretion. Papaverine (0.1-1 mg), aminophylline (0.3-3 mg) and secretin (0.03-0.1 units) also elicited increased secretion. The secretory activity of nicardipine (10 micrograms) was approximately equal to that of 0.5 mg of papaverine, 1.5 mg of aminophylline and 0.03 units of secretin. 3. The concentration of bicarbonate in the pancreatic juice induced by nicardipine was increased, but the protein concentration was only increased slightly. These effects are analogous to those of secretin. 4. Nicardipine-induced secretion was not modified by pretreatment with relatively large doses of phentolamine, propranolol, atropine, guanethidine, haloperidol or metiamide. 5. Secretin-induced secretion was significantly potentiated by infusion of papaverine, but not by infusion of nicardipine or aminophylline. 6. These results suggest that nicardipine acts on the exocrine cells in the dog pancreas, at least in part, through the increase of intracellular cyclic AMP concentration by inhibiting phosphodiesterase activity.

[The effect of mainly alpha-adrenergic drugs, indirect sympathomimetrics and dopamine on exocrine pancreatic function. Studies in the isolated cat pancreas (author's transl)]

The influence of mainly alpha-adrenergic drugs (noradrenaline, adrenaline, phenylephrine), indirect sympathomimetics (ephedrine, tyramin) and dopamine on the exocrine pancreatic function of the isolated perfused organ of cats was studied. The injection of noradrenaline and adrenaline induced simultaneously a rapid depression of flow rate and an increase of perfusion pressure. Phenylephrine, indirect sympathomimetic drugs and dopamine did not change the perfusion pressure and the hydrelatic function (flow rate, secretion of chloride and total calcium). The protein and enzyme secretion was enhanced both in normal animals and cats pretreated by reserpine or 6-hydroxydopamine. The pancreatic protein secretion was inhibited by alpha-adrenolytic as well as beta-adrenolytic substances, tetracain and atropine. It is concluded, that mainly alpha-adrenergic drugs stimulate the pancreatic enzyme secretion in a cholinergic manner.

beta-Adrenoceptor stimulation of exocrine secretion from the rat pancreas

1 Effects of catecholamines given intravenously on exocrine secretion from the pancreas were investigated in anaesthetized rats. The flow rate of pancreatic juice under resting conditions was 11.1 +/- 3.2 microliter per hour in 100 animals. 2 Dopamine (0.3--3 mg/kg) and isoprenaline (1--10 microgram/kg) induced almost the same increase in the pancreatic secretion, so that dopamine was 300 times less potent than isoprenaline. The relative potency of the two amines for stimulation of pancreatic secretion was equivalent to that for beta-stimulation of the contractile force of the left ventricle in vivo. 3 Propranolol (0.5 mg/kg) antagonized completely the dopamine- and isoprenaline-induced stimulation of the pancreatic secretion. 4 Haloperidol (10 mg/kg) failed to suppress the secretory effect of dopamine on the exocrine pancreas but abolished the dopamine-induced hypotension. 5 The dopamine-induced secretion was not modified by atropine (3 mg/kg), phenoxybenzamine (3 mg/kg), vagotomy or pithing. 6 Adrenaline and noradrenaline (10 microgram/kg) induced secretion after phenoxybenzamine treatment (3 mg/kg). 7 It is suggested that the rat pancreas has a stimulatory beta-adrenoceptor mechanism of exocrine secretion.

Circulatory response to systemic infusion of norepinephrine in the pregnant ewe

Seven pregnant ewes from 100 to 137 days of gestation were infused with systemic doses of norepinephrine and uterine arterial flow dose-response curves were determined. A constant infusion of norepinephrine at a mean rate of 0.24 mug per minute per kilogram led to a 39.3 per cent decrease in total uterine arterial blood flow as measured with isotope-labeled microspheres while systemic pressure was unaltered. At this dose the reduction in endometrial blood flow (--64 per cent) was significantly greater than that in either the myometrium (--45 per cent) or placental cotyledons (--31 per cent) (p less than 0.005). Significant decreases in blood flow to small bowel, skeletal muscle, vagina, cervix. Fallopian tubes, kidneys, spleen, pancreas, and mammary gland were documented. There were no significant increases in blood flow. This study demonstrates that during the period or pregnancy studied, the overwhelming response to norepinephrine is vasoconstriction and that the vascular beds of all the tissues of pregnant uterus are sensitive to the alpha-adrenergic effects of norepinephrine.

Hemodynamic effects of norepinephrine and isoprenaline in various regions of the canine splanchnic area

Responses to norepinephrine (NE) and isoprenaline (ISO) (1-1024 ng/kg i.v.) were assessed by electromagnetic flowmetry on 18 arteries of the splanchnic region in anesthetized dogs. Measurements were judged according to the 2 criteria: 1. direction of effect; 2.sensitivity of vascular areas to catecholamines, expressed as D50 (i.e. the calculated dose inducing 50% of the maximum effect). NE decreased flow in all arteries (40-80%), but caused additionally an increase in the celiac, splenic and splenic artery proper. Thus changes in the spleen are responsible for the increase with NE. Flow reduction in the pancreatic branch of the cranial mesenteric artery was small. All flow reductions induced by NE had a similar D50 (about 30 ng/kg), except that in the hepatic artery (100 ng/kg).

Effects of epinephrine on distribution of blood flow in the pregnant ewe

Seven pregnant ewes ranging from 85 to 140 days of gestation were infused with systemic doses of epinephrine and uterine arterial flow dose-response curves were determined. With a constant systemic infusion of epinephrine at a mean rate of 0.29 +/- 0.03 mug/Kg.-min., and the radionuclide lebeled microsphere method to measure arterial blood flow, a 38.5 per cent decrease in total uterine arterial blood flow was demonstrated while systemic pressure was unaltered. At this dose the reduction in endometrial blood flow was significantly greater (-58.7 per cent) than that in either the myometrium (-36.9 per cent) or placental cotyledons (-34.5 per cent) (p less than 0.025 and less than 0.005, respectively). There also occurred a decrease in blood flow to the mammary gland and the pancreas, whereas increased in blood flow to the skeletal muscle, adipose tissue, and spleen were documented. It is evident from this study that during the period of ovine pregnancy investigated, the vascular bed of all tissues comprising the pregnant uterus, including the placental cotyledons, are sensitive to the vasoconstrictive effects of epinephrine.

The kinetics of pancreatic amylase secretion and its relationship to volume flow and electrical conductance in the anaesthetized cat

1. Enzyme secretion in response to short duration vagal stimulation or to rapid I.V. injections of cholecystokinin-pancreozymin (CCK-PZ) or gastrin or to intra-arterial injections of acetylcholine is a function of the volume of juice secreted and not primarily a function of time.2. The output of amylase in response to each stimulus occurred in a constant volume of approximately 15 drops (0.5 ml.) regardless of the rate of background secretin stimulated flow of water and electrolyte.3. It is argued that because amylase secretion occurs in this constant volume, it is due to the rapid secretion of enzyme into the duct system from the acini, and subsequently the secretin stimulated secretion of water and bicarbonate washes the enzyme from the duct system.4. When enzyme secretion is stimulated an increase in the electrical conductance (measured at 1.592 kHz) occurs across the tail of the pancreas. This increased conductance has two components. An early peak associated with the extrusion of enzyme from the acinar cell and a later peak which is probably due to vasodilatation.5. Atropine was without effect on both enzyme secretion and the conductance record when the stimulant was CCK-PZ. Atropine blocked enzyme secretion and both peaks of the conductance record in response to stimulation by acetylcholine. Atropine blocked enzyme secretion and abolished the early phase of the conductance record, on vagal stimulation. It was without effect on the later peak which probably indicates an atropine resistant vasodilation of the pancreatic vessels.6. When the vagus is stimulated on a background of submaximal electrolyte secretion caused by the intravenous infusion of secretin, the volume rate of secretion and the rate of amylase secretion follow a similar time course. The maximal volume response occurred between 7 Hz and 15 Hz and the maximal amylase output per impulse was at 5 Hz.

Prostaglandin action on pancreatic blood flow and on electrolyte and enzyme secretion by exocrine pancreas in vivo and in vitro

1. Intra-arterial injection or infusion of prostaglandins E(1) and E(2) into anaesthetized cats caused a fall in arterial blood pressure, a reduction in pancreatic blood flow and an inhibition of secretin-stimulated pancreatic electrolyte secretion. In some experiments these effects were preceded by a transient increase in blood flow and secretion.2. The fall in blood pressure and reduction in blood flow, but not the inhibition of secretion, were much less marked following administration of the alpha-adrenergic blocking agent phenoxybenzamine.3. Prostaglandins F(1alpha) and F(2alpha) caused only a slight reduction in blood pressure and had very little effect on pancreatic blood flow or electrolyte secretion.4. Addition of prostaglandins to the perfusate of the saline-perfused cat pancreas stimulated electrolyte secretion, with E(1) = E(2) >> F(1alpha) = F(2alpha). This stimulatory action was markedly potentiated by theophylline.5. Enzyme secretion was not stimulated by any of the prostaglandins, even in the presence of theophylline.6. It is concluded that prostaglandins can stimulate electrolyte transport by exocrine pancreas, perhaps through a mechanism involving adenylate cyclase, but that in vivo this action is masked by a secondary inhibition resulting either from vasoconstriction, or from the libration of an antisecretory agent, or both.