Characteristics of the axonal transport of vasoactive intestinal polypeptide (VIP) in nerves of the cat

The axonal transport of vasoactive intestinal polypeptide (VIP) was examined in anesthetized cats. The distally directed (anterograde) flux of peptide was found to be about 35 fmol/h in the sciatic nerve. A smaller retrograde flux (8.5 fmol/h) weas also detected. In ulnar, radial and sciatic nerves, the average velocity of transport was calculated to be 2.5 mm/h in the anterograde and 0.6 mm/h in the retrograde direction. Clearance experiments indicated that the amounts of peptide available for transport in these two phases were 28% and 15% of the total, respectively. Estimates of true velocity based on these figures are 9 mm/h for anterograde transport and 4 mm/h for retrograde transport. Local injections of vinblastine were found to induce marked local increases in VIP-immunoreactivity, indicating that microtubules play a role in peptide transport. Subcellular distribution experiments showed that most of the transported VIP was associated with a particulate fraction, possibly corresponding to large vesicles. Only one molecular form of VIP-immuno-reactivity was detected by gel permeation chromatography and no evidence was obtained for cleavage of VIP precursors in the axon. Comparison of axonal flux of peptide with the apparent content of VIP in terminal regions indicated that the turnover time for this peptide is 5 days or longer in the periphery. The results are consistent with the view that peripheral neurons are dependent upon rapid axonal transport for the supply of vip to their terminals.

Effect of vasoactive intestinal polypeptide (VIP) upon myometrial blood flow in non-pregnant rabbit

Vasoactive intestinal polypeptide (VIP) containing nerve fibres have previously been demonstrated in the female genital tract of several mammalian species including the rabbit. These nerve fibres seemingly innervate vascular and non-vascular smooth muscle. For that reason we investigated the dose-relationship between VIP (5, 50, 500 pmol . min-1 . kg-1) and myometrial blood flow (MBF) using Xenon-133 washout technique. VIP increased MBF dose-dependently. VIP was on molar base 100 times more potent than acetylcholine. The action of VIP seems to be direct on vascular smooth muscle rather than mediated by other neurotransmitters, because the MBF increase was not antagonized by atropine, adrenergic blocking agents or naloxone. These findings make it likely that VIP plays a role in the local nervous control of myometrial blood flow.

Infusion of vasoactive intestinal polypeptide in man: pharmacokinetics and effect on gastric acid secretion

Elimination and effect on acid secretion of vasoactive intestinal polypeptide (VIP) were studied in six healthy volunteers. On a background infusion of pentagastrin, 100 ng/kg-h, VIP was administered as stepwise intravenous infusions in doses of 0.5, 0.9, and 2.7 micro/g/kg-h, each dose being give for 1 h. Mean plasma VIP concentrations rose from 5.7 pmol/l to 28, 106 and 336 pmol/l during the VIP infusions. No significant changes in acid secretion occurred during VIP infusion as compared to infusion of pentagastrin alone, and no duodeno-gastric reflux was registered. Serum gastrin concentrations were unaltered during VIP infusion. Elimination of VIP was bi-exponential with half-lives of 2 and 21 min, respectively. Metabolic clearance rate was 42 ml/kg-min and the estimated volume of distribution 135 ml/kg.

Secretory effects of cholecystokinins on the isolated perfused porcine pancreas

Three different molecular forms of cholecystokinin (CCK-39, -33, and -8) were used in concentrations from 10(-11) to 19(-8) mol/l to stimulate the endocrine and exocrine secretion from the isolated perfused porcine pancreas. During perfusion with a glucose concentration of 7.5 mmol/l CCK-39 in the highest concentration increased the insulin secretion slightly. No significant effect was observed at lower glucose concentrations (5.0 and 3.5 mmol/l). CCK-33 and -8 did not stimulate the secretion of insulin significantly, and neither of the cholecystokinins increased the secretion of glucagon and bicarbonate. All three molecular forms stimulated the secretion of fluid and protein in concentrations above 10(-11) mol/l in a dose-dependent manner and with equal potency. We conclude that the effect of these three cholecystokinins on the endocrine pancreas is without physiological significance, whereas all three are sufficiently potent to play a role in the control of pancreatic protein secretion.

Nervous control of pancreatic endocrine secretion in pigs. III. The effect of acetylcholine on the pancreatic secretion of insulin and glucagon

We studied the effect of intraarterial administration of acetylcholine on insulin and glucagon secretion in anesthetized splanchnicotomized pigs and on insulin, glucagon, and pancreatic polypeptide secretion from the isolated perfused porcine pancreas and the isolated perfused duodeno-pancreatic block of pigs and dogs. In the pigs acetylcholine stimulated insulin and glucagon secretion in a glucose dependent manner similar to vagal stimulation; however, the response was completely resistant to hexamethonium and abolished by atropine. Acetylcholine stimulated insulin and pancreatic polypeptide secretion of the isolated perfused porcine pancreas, and inhibited glucagon secretion, whether the duodenum was present or not, whereas the glucagon secretion of the isolated perfused canine pancreas was stimulated by acetylcholine.

Hypersecretion of calcitonin in patients with the Verner-Morrison syndrome

Three patients with the Verner-Morrison syndrome due to pancreatic tumours are reported; all had an overproduction of calcitonin and hypercalcemia. In two cases the hypercalcitoninaemia was due to an ectopic secretion from the pancreatic tumour, but in one the source could not be determined with certainty. Hypercalcemia in the Verner-Morrison syndrome might be due to simultaneous hyper-parathyroidism (MEA I) or secretion from the tumour of a substance or substances with calcium-elevating properties. Streptozotocin was of beneficial value in treating these patients. None of the patients became diabetic or had any other side effects of the therapy except for nausea and vomiting.

Nervous control of pancreatic endocrine secretion in pigs. II. The effect of pharmacological blocking agents on the response to vagal stimulation

The glucose dependent glucagon and insulin responses to electrical vagal stimulation in anesthetized splanchnicotomized young pigs were studied after administration of various pharmacological blocking agents. Hexamethonium completely abolished the responses, regardless of the glucose level. Atropine was without effect on the glucagon as well as the insulin response, regardless of stimulation frequency, glucose level, or dose of atropine. Neither propranolol nor a combination of propranolol and phenoxybenzamine inhibited the response. Our findings indicate that neither adrenergic fibres nor fibres impinging on muscarinic cholinergic receptors are involved in the pancreatic endocrine response to vagal stimulation.

Nervous control of pancreatic endocrine secretion in pigs. I. Insulin and glucagon responses to electrical stimulation of the vagus nerves

The increases in the concentrations of insulin and pancreatic glucagon in portal venous and arterial plasma in response to electrical stimulation of the vagus nerves were studied in anesthetized splanchnicotomized young pigs. The responses were frequence dependent; threshold frequency was below 1 Hz and maximum response was reached at 8-12 Hz. With maximal stimulation responses of magnitudes comparable to the responses to maximal arginine (glucagon) and glucose stimulation (insulin) were observed. However, both the insulin and the glucagon response were critically dependent on the blood glucose concentration during the stimulation: the glucagon response was inversely correlated to blood glucose, whereas the insulin response was positively correlated to blood glucose at concentrations above 4.5 mmol . 1(-1). Below this glucose concentration there was no detectable insulin response and above 8.0 mmol . 1(-1) no glucagon response to vagal stimulation. A stimulated secretion of glucagon as well as insulin was maintained for up to 30 min stimulation, but insulin secretion tended to decrease, whereas glucagon secretion tended to increase. Above blood glucose concentrations of 4 mmol . 1(-1), blood glucose concentrations increased slightly in response to vagal stimulation, whereas no change was noted during stimulations performed at lower blood glucose concentrations.

Increased myometrial blood flow evoked by vasoactive intestinal polypeptide in the non-pregnant goat

1. The effect of vasoactive intestinal polypeptide (VIP) on myometrial blood flow was evaluated in anaesthetized goats. A solution of VIP, or vehicle alone, was infused into the right internal iliac artery for a period of 10 min. The myometrial blood flow in both uterine horns was measured from the third to the seventh min of the infusion by the gas clearance technique after local injection of (133)xenon in 10 mul. saline solution. Blood samples were collected from both utero-ovarian veins 5 min from the onset of the infusion and the plasma concentration of VIP determined by radio-immunoassay.2. During infusion of vehicle before VIP, myometrial blood flow was of the same magnitude in both uterine horns, i.e. 0.06-0.12 ml./min per g. The blood flow of the right horn increased to 0.20-0.39 ml./min per g during infusion of VIP (300 p-mole/min) in the ipsilateral artery, whilst that of the left horn rose to 0.13-0.26 ml./min per g. The effect was sometimes observed to last for more than 40 min.3. Increased myometrial blood flow was observed with infusion rates down to 3 p-mole/min. Once a response to VIP had been provoked, however, the vasculature sometimes became refractory to further stimulation.4. The plasma concentration of VIP increased in both utero-ovarian veins during unilateral infusion of the peptide.5. Methylene blue given through the infusion catheter stained tissue in both uterine horns, further evidencing that their blood supply is not entirely separate.6. Uterine motility was observed to diminish during the VIP infusions.7. During infusion of VIP (300 p-mole/min) heart rate rose from 146 +/- 6 to 158 +/- 7 beats/min. No significant change occurred in arterial blood pressure.8. It is concluded that the increase in blood flow is due to a local response and that, since VIP has been demonstrated in uterine nerve endings, it may act as a neuro-transmitter mediating vasodilatation in the uterus.

Meal-stimulated secretin release in man: effect of acid and bile

Nine normal subjects were studied before and after intragastric instillation of a liquid meal. Gastric emptying rates of acid and pancreaticobiliary secretions were quantitated by means of a dilution indicator technique. A significant, positive correlation was found between load of acid to the duodenum and the concentration of secretin in plasma. No correlation was found between load of the bile acids and plasma secretin. The buffering capacity of gastric contents should be taken into account when fasting and postprandial periods are compared. Plasma secretin concentration remained low during the first postprandial hour. Maximum secretin concentrations and duodenal disappearance rate of acid was observed 1 1/2-2 h after instillation of the meal. In contrast, trypsin output was maximum within 10 min. The data support the concept that in man release of secretin is governed principally by the amount of hydrogen ions emptied into duodenum and indicate the importance of secretin in the late postprandial period, when the acidity of the gastric contents is high.

Distribution and motor effect of VIP in female genital tract

The distribution and concentration of vasoactive intestinal polypeptide (VIP) in different parts of the female genital organs from various species (cat, goat, pig, rabbit, rat, and guinea pig) were studied by means of immunohistochemistry and immunochemistry. In addition, the effect of VIP on the mechanical activity of uterine muscle was investigated in vitro. VIP immunoreactive nerve fibers innervating vessels and smooth muscle cells were fairly numerous in the genital organs of the cat and goat and less numerous in the pig, rabbit, rat, and guinea pig. In all species studied, VIP-containing nerves were most numerous in the cervix. The tissue concentration of VIP measured by immunochemistry was in agreement with the immunohistochemical findings. VIP inhibited the mechanical uterine activity in the cat, goat, pig, and rabbit, whereas only minimal effects were obtained in the rat and guinea pig. This difference between the species corresponded to the number of VIP-containing nerves in the uterine muscle. The data support the hypothesis that VIP may play a physiological role in the local nervous control of the uterine mechanical activity.

Vasoactive intestinal polypeptide (VIP) in epithelial cells of the gut mucosa of an elasmobranchian cartilaginous fish, the ray

As part of study of the phylogeny of VIP, it was observed that the colonic mucosa of the cartilaginous fish, Raja radiata and Raja clavata, contained numerous epithelial cells, obviously of closed type, displaying intense VIP immunoreactivity. Accordingly, high concentrations of VIP were found by radioimmunoassay. At the ultrastructural level, the VIP cells were characterized by the presence of highly electron dense secretory granules. The colonic mucosa of the ray may be a good source for the isolation of an early VIP.

Effects of VIP in the female genital tract

Vasoactive Intestinal Polypeptide (VIP) has been demonstrated in the female genitourinary tract, localized in neurons which seem to innervate vessels and non-vascular smooth muscle. The present work has demonstrated that the concentration of immunoreactive VIP varies between different mammalian species and within the genital tract of the same species. Using various in vivo and in vitro preparations the peptide was found to have a dose-dependent inhibitory effect on the myoelectrical activity and contractility of the uterine muscle, and to increase myometrial blood flow. The findings support the hypothesis that VIP may play a physiological role in the local control of uterine motility and blood flow.

Reduced cortical choline acetyltransferase activity in senile dementia of Alzheimer type is not accompanied by changes in vasoactive intestinal polypeptide

Post-mortem brain tissue from 7 patients who died with a diagnosis of senile dementia of Alzheimer type (SDAT) was compared with tissue obtained from 7 control patients at routine post mortem. A significant fall in choline acetyltransferase (ChAT) activity was apparent in the cerebral cortex of the SDAT cases which was maximal in the temporal lobe. The fall in ChAT activity was not accompanied by changes in cortical vasoactive intestinal polypeptide (VIP) measured by radioimmunoassay.

Concentration of immunoreactive trypsin and activity of pancreatic isoamylase in serum compared in pancreatic diseases

We measured the concentration of immunoreactive trypsin and the enzymic activity of pancreatic isoamylase in sera from 103 patients with pancreatic diseases and 29 other subjects serving as a reference group. Almost all patients with pancreatic diseases had abnormal values for both enzymes. A strong positive correlation between these two variables over a 1000-fold range was observed.

Concentration of immunoreactive trypsin and activity of pancreatic isoamylase in serum compared in pancreatic diseases

We measured the concentration of immunoreactive trypsin and the enzymic activity of pancreatic isoamylase in sera from 103 patients with pancreatic diseases and 29 other subjects serving as a reference group. Almost all patients with pancreatic diseases had abnormal values for both enzymes. A strong positive correlation between these two variables over a 1000-fold range was observed.

VIP occurs in intrathyroidal nerves and stimulates thyroid hormone secretion

Vasoactive intestinal polypeptide (VIP) is known to have powerful effects on the secretion from several endocrine and exocrine glands, and occurs in nerves with a ubiquitous distribution in the body. This infers that neuronal VIP may be a regulator of such secretion, and there is evidence that it is involved in the regulation of exocrine pancreatic function. Previous studies have shown that adrenergic and cholinergic nerves participate in the regulation of thyroid hormone secretion. We describe here combined immunohistochemical and immunochemical studies which show that the thyroid of several species is supplied with VIP-containing nerve fibres that surround blood vessels and run between and along thyroid follicles and that in the mouse neuronal VIP participates in the regulation of thyroid hormone secretion through a mechanism that is mediated by cyclic AMP.

Gastroenteropancreatic hormonal changes during exercise

Peripheral plasma concentrations of gastroenteropancreatic peptides were measured during a 3-h period of bicycle exercise at 40% of maximal oxygen uptake in six normal men. Marked increases (P < 0.02) were found in vasoactive intestinal polypeptide (VIP) [1.8 +/- 0.7 (rest) vs. 22.3 +/- 5.4 pmol x l-1 (mean +/- SE) (3 h)], secretin (0.5 +/- 0.5 vs. 11.1 +/- 2.7 pmol x l-1), pancreatic polypeptide (PP) (4.0 +/- 1.5 vs. 46.3 +/- 11.5 pmol x l-1), somatostatin (SRIF) (12.8 +/- 1.2 vs. 17.7 +/- 0.6 pmol x l-1), whereas no changes occurred in gastric inhibitory polypeptide (37.3 +/- 5.9 vs. 39.2 +/- 9.8 pmol x l-1). Immunoreactive insulin and C-peptide decreased from 0.08 +/- 0.004 and 0.39 +/- 0.03 pmol x l-1, respectively, to 0.04 +/- 0.003 (P < 0.005) and 0.13 +/- 0.02 (P < 0.001). The significant decrease in C-peptide and in the C-peptide-to-insulin molar ratio indicate decreased insulin secretion and clearance, respectively, during exercise. Plasma glucose decreased [5.0 +/- 0.1 (rest) vs. 4.2 +/- 0.3 mmol.l-1 (3 h)] (P < 0.01). During 3 h of rest, none of the measured parameters had changed. The marked exercise-induced changes in plasma concentrations of PP, secretin, VIP, and SRIF are provocative. We know in detail neither the stimuli for the release of these peptides nor their physiological role during exercise.

Neuronal VIP in salivary glands: distribution and release

Nerves containing vasoactive intestinal peptide (VIP) were observed in salivary glands of rat, cat and man. VIP nerves were numerous in the cat while they were moderate in number in rat and man. The measured concentrations of immunoassayable VIP were in agreement with the immunohistochemical findings. Electrical stimulation of the feline chorda lingual nerve, which stimulates salivary secretion and local blood flow, resulted in a marked elevation of VIP in the venous effluent from the submandibular gland. VIP was not measurable in saliva. Gel permeation chromatography of extracts from cat submandibular gland and from venous plasma collected before and during nervous stimulation revealed one immunoreactive peak with an elution position identical to that of highly purified porcine VIP. The finding of neuronal VIP in salivary glands, its release upon nerve stimulation and its known effect on local blood flow support the view that VIP is a neurotransmitter in the salivary glands.

VIP (vasoactive intestinal polypeptide)-containing nerves of intracranial arteries in mammals

Immunohistochemical and radioimmunochemical investigations have shown, in various species, the occurrence of numerous nerve fibres containing vasoactive intestinal polypeptide (VIP) in connection with blood vessels of the central nervous system. Pial arteries from pig, cat, and rat have the richest supply of VIP nerve fibres; those of cow, dog guinea pig and hamster have an intermediary number of nerves, while only few are found in pial arteries from the monkey, rabbit, gerbil, and mouse. The regional variation in VIP-nerve density follows the order: cerebral arteries greater than basilar greater than vertebral greater than spinal cord arteries. Unilateral extirpation of either the pterygopalatine or the superior cervical ganglia does not affect the amount or distribution of VIP fibres in the wall of brain vessels of the ipsilateral side. Measurement of the VIP content by radioimmunoassay shows mean concentrations in the pial arteries varying between 19 and 82 pmol/g tissue wet weight. Regional and species variations in measured VIP levels are similar to the variations in distribution of immunoreactive nerve fibres.

Vasoactive intestinal polypeptide, 5-hydroxytryptamine and reflex hyperaemia in the small intestine of the cat

1. The release of vasoactive intestinal polypeptide (VIP) into venous blood from the small intestine of the cat was studied when mechanically stimulating the intestinal mucosa and during close intra-arterial infusions of 5-hydroxytryptamine (5-HT) or isopropylnoradrenaline. The studies were performed on anaesthetized cats given atropine.2. Mechanical stimulation of the intestinal mucosa induced a vasodilatation and a release of VIP into the intestinal venous blood. Intra-arterial administration of tetrodotoxin was given in doses that blocked the vasoconstrictor effect of the regional sympathetic nerve fibres. This also abolished the vascular response and the release of VIP into blood upon mechanical stimulation.3. Close intra-arterial administration of 2-bromo-lysergic acid diethylamide reduced the VIP release and the intestinal vasodilatation upon mucosal stimulation to largely the same extent.4. Close intra-arterial infusions of 5-HT produced a marked release of VIP from the intestine and a moderate vasodilatation. Close intra-arterial infusions of isopropylnoradrenaline, which caused a pronounced intestinal vasodilatation, evoked only a small release of VIP.5. The results are compatible with the hypothesis that the vasodilatation in the gut, induced by mechanical mucosal stimulation, is mediated via an intramural nervous reflex containing a neurone capable of releasing VIP. It is proposed that the nervous reflex is activated by the release of 5-HT from the enterochromaffin cells evoked by mechanical stimulation of the mucosa.

Vasocative intestinal polypeptide (VIP)-producing ganglioneuroma in a child with chronic diarrhea

In a 2 1/2-year-old girl with persistent watery diarrhea a retroperitoneal tumour and lymph node composed of benign ganglioneuroma cells were found. The histological picture was compatible with an original metastasizing neuroblastoma which has passed through a stage of late maturation. Electron microscopy of the ganglioneuroma showed cytological evidence of increased secretory activity. The tumour contained large amounts of vasoactive intestinal polypeptide (VIP) and preoperative plasma concentration of this peptide was increased. Postoperatively the VIP concentration was normalized, and the diarrhea ceased. Analysis of catecholamine metabolites in urine was normal. The findings suggest that the watery diarrhea was due to the benign VIP-producing neural crest tumour.

Effect of VIP infusion in water and ion transport in the human jejunum

Infusion of vasoactive intestinal polypeptide (VIP) is known to cause intestinal secretion in animal models. The present study was designed to answer the question whether VIP has a similar effect on the human intestine. Pure porcine VIP was administered by constant i.v. infusion to healthy subjects while their jejunum was perfused with a plasma-like electrolyte solution. At the lowest VIP infusion rate (100 pmol/kg/hr), plasma VIP levels rose two- to four-fold, and there was an increase in the transmucosal potential difference but no change in sodium chloride absorption. At higher VIP infusion rates (200 and 400 pmol/kg/hr), VIP plasma concentrations rose to levels commonly observed in patients with pancreatic cholera syndrome. At these levels VIP caused a dose-dependent decrease of water and sodium absorption. Chloride absorption changed to secretion, while bicarbonate movement remained completely unaffected. Chloride secretion was active, since it occurred against an electrical and chemical gradient. All changes induced by VIP were reversible after discontinuance of VIP infusion. Our observations suggest that elevated levels of circulating VIP are capable of affecting water and ion movement in the human jejunum. They lend support to the hypothesis that high levels of circulating VIP may be a mediator of secretory diarrhea in some patients with pancreatic cholera syndrome.

Vasoactive intestinal polypeptide (VIP) inhibits prostaglandin-F2 alpha-induced activity of the rabbit myometrium

Seven female rabbits ahd myometrial autografts transplanted into ear-chambers. The electrical activity of the graft was recorded and mechanical activity observed. Vasoactive intestinal polypeptide (VIP) dose-dependently inhibited myometrial activity induced by prostaglandin-F2 alpha. This evidence and the occurrence of "VIPergic" nerve fibres, which seem to innervate the myometrial cells, suggest that VIP may play a physiological role in the local control of the myometrial activity.

Vasoactive intestinal polypeptide in cholinergic neurons of exocrine glands: functional significance of coexisting transmitters for vasodilation and secretion

By a combination of the indirect immunofluorescence technique with acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) staining, it was shown that vasoactive intestinal polypeptide (VIP) is present in cholinergic (acetylcholinesterase-rich) neurons involved in control of secretion and vasodilation in exocrine glands of cat. The submandibular salivary gland was used as a functional model. Preganglionic nerve stimulation induced an atropine-resistant, hexamethonium-sensitive vasodilation and release of VIP into the venous outflow from the gland and an atropine- and hexamethonium-sensitive secretion. Infusion of VIP antiserum reduced both the vasodilation and secretion. Infusion of VIP caused vasodilation only, whereas acetylcholine caused both vasodilation and secretion. Simultaneous infusion of VIP and acetylcholine in low doses resulted in a marked potentiation of both vasodilation and secretion. The present morphological and functional data support the following hypothesis for regulation of vasodilation and secretion in exocrine glands. Preganglionic cholinergic nerves activate, via nicotinic receptors, postganglionic neurons, causing concomitant release from the same nerve endings of two coexisting putative transmitters, acetylcholine and VIP. Acetylcholine produces mainly secretion by a muscarinic action and VIP causes mainly vasodilation, but the two substances seem to cooperate directly or indirectly in both types of response. Thus, the coexistence of two putative neurotransmitters, VIP and acetylcholine, in one neuron may explain the dual effector response (i.e., the cholinergic secretion and the atropine-resistant vasodilation) caused by nerve stimulation in exocrine glands.

Secretory effects of gastrins on isolated perfused porcine pancreas

The effects of the four main forms of gastrin (component I, gastrin-34, gastrin-17, and gastrin-14) on insulin, glucagon, and exocrine secretion were measured on the isolated perfused porcine pancreas. All gastrins were studied in concentrations ranging from 10(-11) to 10(-8) M. Depending on the glucose concentration in the perfusate, all four gastrins increased insulin or glucagon secretion in a dose-dependent manner in concentrations above 10(-10) M. These concentrations are slightly above the arterial concentrations in normal pig and man, but they correspond to gastrin concentrations measured in patients with achlorhydria and gastrinomas. The exocrine secretion was stimulated by all gastrins in a dose-dependent manner. The lowest concentrations that stimulated flow rate significantly were within the physiologic range, 10(-11) and 10(-10) M. All gastrins induced maximal flow rate at a concentration of 10(-9) M. The sulfated form of gastrin-17 had the greatest efficacy. The results indicate that all gastrins may influence the exocrine secretion under normal conditions and the endocrine secretion in diseases with endogenous hypergastrinemia.

Vasoactive intestinal polypeptide (VIP) in cirrhosis: arteriovenous extraction in different vascular beds

The concentration of vasoactive intestinal polypeptide (VIP) was determined in peripheral venous plasma from 136 patients with liver cirrhosis without gastrointestinal bleeding or coma and from 112 controls. In eight patients (cirrhosis, six; fibrosis, one; steatosis, one) arteriovenous extraction or release of VIP was measured during catheterization at four locations: brain, lower limb, intestine-liver, and kidney. The mean concentration of VIP in peripheral venous plasma from patients with cirrhosis was 9.4 pmol/l (median, 7.0; range, 0-86), which was significantly higher than that of the controls, who had a mean of 6.2 pmol/l (median, 6.0; range, 0-20, P less than 0.01). No significant extraction or release of VIP could be detected across the vascular bed in brain or lower limb. A significant arterio-hepatovenous VIP extraction ratio (mean, 0.43; range, 0.05-0.87) confirmed at net splanchnic elimination of VIP from extra-splanchnic areas and from porto-systemic shunting of VIP in cirrhosis. The net splanchnic elimination rate of VIP was estimated to be about 3 pmol/min. The concentration of VIP in ascitic fluid was on the average three times that of arterial plasma. In conclusion, VIP is significantly elevated in peripheral plasma from patients with cirrhosis, probably due to porto-systemic shunting and/or compromised hepatic elimination. Hepatic elimination is still likely to account for the inactivation of most of the VIP escaping from the neurosynapses throughout the body in patients with cirrhosis without coma.

Axonal transport of neuropeptides in the cervical vagus nerve of the rat

Accumulations of the neuropeptides substance P (SP), somatostatin (ST), and vasoactive intestinal polypeptide (VIP) proximal to a crush in the cervical vagus nerve of the rat have been measured using sensitive radioimmunoassays. Each of the peptides was rapidly transport towards the peripheral terminals of vagal afferent fibres, with average rates of flow ranging from 0.8 to 2.7 mm h-1. In the rabbit vagus nerve, SP was transported with an average rate of 4 mm h-1, which is more than double the rate for this peptide in the rat. Double crush experiments in rabbit vagus nerves indicated that the rapidly transported proportion of the total content of SP in the nerve free was about 34%. From this, the rate of transport of SP in the rapidly transported pool in the rabbit vagus nerve can be calculated to be 12 mm h-1 (280 mm day-1). Since such double crush experiments were not possible in the rat, it is not clear whether the different average rates of transport of SP in the rat and the rabbit reflect real differences in the rate of rapid transport in the two species. In common with rapid axonal transport of other neurotransmitters, the transport of SP and ST in the rat vagus nerve was blocked by colchicine, a drug that disrupts microtubules.

Vasoactive intestinal polypeptide in vagally mediated pancreatic secretion of fluid and HCO3

The role of nerves that liberate vasoactive intestinal polypeptide (VIP) in the porcine pancrease as mediators of the atropine-resistant action of the vagus on flow and bicarbonate (HCO3) secretion was examined. Efferent electrical stimulation of the vagus in atropinized pigs produced a profuse flow of pancreatic juice with high HCO3 content concomitantly with a significant increase in pancreatic VIP output from 13 to 113 fmol/min. Intravenous administration of somatostatin (SRIF) during continuous electrical vagal stimulation caused a parallel suppression of the VIP release and the pancreatic fluid and HCO3 secretion to prestimulatory values. The SRIF-induced reduction in fluid and HCO3 secretion seemed to be mediated via an inhibition of the VIP release rather than through a direct effect on the exocrine cells, inasmuch as SRIF did not influence the VIP-provoked exocrine response from the in vitro isolated perfused porcine pancreas. The results support the view that VIP is transmitter in the vagally induced atropine-resistant water and HCO3 secretion from the porcine pancreas.

Development of vasoactive intestinal polypeptide (VIP) containing neurones in the rat brain

The development of VIP-containing neurones in the rat CNS and duodenum has been studied using a specific radioimmunoassay and immunohistochemistry. In the brain, VIP immunoreactivity appears entirely postnatally, while VIP in peripheral neurones in the duodenum was present before birth. The developmental changes observed in cerebral cortex appear to represent the maturation of a population of intrinsic cortical interneurones which contain VIP. These neurones develop entirely after birth. They are first seen in deep cortical layers, but later spread out into all cortical layers, particularly layers II--IV. Changes in the intensity of VIP cell body fluorescence can be correlated with changes in VIP content in the cortex measured by radioimmunoassay. Thus VIP forms a unique chemical marker for studying the maturation of a cortical neurone.

Effect of kainic acid injections and other brain lesions on vasoactive intestinal peptide (VIP)-stimulated formation of cAMP in rat brain

In rat striatal slices, both intrastriatal kainic acid injection, which destroys striatal neurones, and intranigral injection of 6-hydroxydopamine (6-OHDA), which leads to a degeneration of dopamine nerve terminals in the striatum, reduced vasoactive intestinal peptide (VIP)-induced cAMP accumulation by approximately 60%. Cortical ablation, which leads to degeneration of cortico-striatal fibres, had no effect on striatal VIP-induced cAMP formation. Knife cut lesions transecting the stria terminalis, which destroy afferent fibres to the amygdala, decreased the VIP-induced increase in cAMP in amygdala slices by 40%, while kainic acid injection into the amygdala had no effect. Kainic acid injection into several other brain regions, including hippocampus, cortex and hypothalamus also failed to affect the VIP-elicited increase in cAMP in slices, despite reductions in choline acetyl-transferase, glutamate decarboxylase, cyclic nucleotide phosphodiesterase and basal levels of cAMP. The results of a study of the effects of various VIP fragments on cAMP stimulation in striatal and cortical slices suggests that the entire sequence of VIP is necessary for full activity. The results suggest that VIP may be involved in neuromodulation or neurotransmission in the striatum and/or nigrostriatal pathway and also in the stria terminalis from the bed nucleus to the amygdala.

Physiological significance of secretin in the pancreatic bicarbonate secretion. I. Responsiveness of the secretin-releasing system in the upper duodenum

In nine normal subjects intraduodenal pH was measured by means of a glass electrode placed in the passage from the first to the second part of the duodenum. The physiological variations in pH were simulated by intraduodenal injection of 2.5, 5, or 10 ml of 0.1 mol x 1(-1) HCl and subsequent neutralization by injection of bicarbonate. A total of 26 injections of acid was followed by a pH spike from a median pH of 7.0 to a median of pH 2.1 Median spike duration was 45 sec. The concentration of secretin in plasma increased from a median of 1.2 pmol x 1(-1) to a peak value of 2.2 pmol x 1(-1) after 4 min. It is concluded that the secretin response to a brief acidification of the first 4--6 cm of the duodenum is sufficient to explain the physiological variations in the concentration of secretin in human plasma.

Vasoactive intestinal polypeptide: measurement, distribution and putative neurotransmitter function

Vasoactive intestinal polypeptide (VIP) is a highly basic octacosapeptide isolated from porcine small intestine. VIP was originally considered to be a gut hormone, but radioimmunochemical and immunohistochemical studies have revealed that VIP has a widespread distribution localized in neurons. VIP-containing neurons are present in the central nervous system including the cerebral arteries, the digestive tract, the genitourinary tract and the adrenal glands. In the nerve terminals VIP is localized in synaptic vesicles. VIP fulfils a number of criteria to be a neurotransmitter both in central and peripheral nerves. Whilst the role of VIP in the central nervous system is unknown, it is likely that VIP is the mediator of gastrointestinal and pancreatic functions, which are controlled by non-cholinergic, non-adrenergic nerve fibres.

Fat-induced jejunal inhibition of gastric acid secretion and release of pancreatic glucagon, enteroglucagon, gastric inhibitory polypeptide, and vasoactive intestinal polypeptide in man

The effect of intrajejunal (i.j.) infusion of fat on meal-stimulated gastric acid secretion and release of pancreatic glucagon (PG), enteroglucagon (EG), gastric inhibitory polypeptide (GIP), and vasoactive intestinal polypeptide (VIP) was studied in seven healthy volunteers. I.j. fat markedly inhibited meal-stimulated acid secretion as compared to a control study with i.j. saline infusion. The acid inhibition was accompanied by augmental plasma concentrations of EG, GIP, and VIP but not of PG, suggesting that EG, GIP, and VIP may be among mediators of fat-induced jejunal inhibition of acid secretion. Concentration-time relationship makes it unlikely that the observed inhibition could be ascribed to any single peptide studied.

Physiological significance of secretin in the pancreatic bicarbonate secretion. II. Pancreatic bicarbonate response to a physiological increase in plasma secretin concentration

The pancreatic response to physiological concentrations of secretin obtained after minute boluses of exogenous secretin was studied in 16 normal volunteers. Output of bicarbonate into the duodenum was measured by duodenal aspiration in 5 subjects and by endoscopic cannulation of the pancreatic duct in 11 subjects. Pure natural porcine secretin was injected intravenously in doses of 125, 250, and 500 fmol x kg-1 body weight (0.0013, 0.0027, and 0.0054 clinical units x kg-1). All three doses of secretin increased plasma secretin concentration, duodenal bicarbonate concentration, and duodenal bicarbonate output significantly. The bicarbonate output measured by the two techniques did not differ significantly. The increments in median plasma secretin concentration were 1.6, 3.0, and 6.4 pmol x 1(-1) after secretin, 125, 250 and 500 fmol x kg-1, and the corresponding 15-min bicarbonate output 283, 442, and 1435 micromol, respectively. The concentrations of secretin in plasma found after these doses of secretin are of the same order of magnitude as the secretin concentrations found during physiological conditions in man. It is concluded that the physiological concentrations or secretin influence pancreatic bicarbonate secretion.

Nervous control of pancreatic exocrine secretion in pigs

The pancreatic secretion of fluid, bicarbonate and protein in response to electrical stimulation of the vagus and splanchnic nerves, to exogenous and endogenous secretin and to various pharmacological agents was studied in anesthetized young pigs (21 kg). Vagal stimulation increased flow, bicarbonate output and protein output in a frequency dependent manner; the half maximal effective frequency was 2--4 Hz and the maximal effective frequency 12 Hz. The secretory response to vagal stimulation was potentiated by physiological elevations of the arterial concentration of secretin brought about by injection of secretin or by acidification of the duodenal bulb. Simultaneous stimulation of the splanchnic nerves strongly inhibited the response to vagal stimulation; splanchnic nerve stimulation alone had no demonstrable effect. The flow and bicarbonate response to vagal stimulation was unaffected by atropine, but abolished by hexamethonium. Protein output was strongly inhibited by both agents. The response to intraarterial infusion of acetylcholine resembled that elicited by vagal stimulation but it was smaller and it was completely abolished by atropine and unaffected by hexamethonium. Alpha- and beta-adrenergic blockade stimulated rather than inhibited the secretory response to vagal stimulation. The portal vein plasma concentration of secretin was not affected by vagal stimulation. The results indicate that the protein response, and the flow and bicarbonate response to vagal stimulation are not brought about by the same mechanism. An increased release of secretin is not involved. Peptidergic (VIP-containing) nerves may contribute.