[Pancreatic polypeptide (a review of the literature)]

The article is a review of the information available at present of the pancreatic polypeptide (PP) including its structure, localization, stimulators and inhibitors of its release, physiological and pharmacological action on the gastrointestinal tract, mechanisms of PP release in response to a meal and during digestion. The data on PP level in pancreatic diseases are presented as well. The opinion is expressed of PP physiological role in the regulation of gastrointestinal tract functions.

The effect of truncal vagotomy on the response of the canine lower esophageal sphincter to varying doses of pancreatic polypeptide

Lower esophageal sphincter pressure (LESP) and plasma pancreatic polypeptide (PP) levels increase after ingestion of a protein meal. This study was done to determine whether an increase in LESP would occur during intravenous administration of exogenous PP at physiologic and pharmacologic doses and whether the integrity of vagal innervation would alter the response. Manometric observations were made, in each of five dogs, of the LESP before and during intravenous infusion of bovine PP at doses ranging from 0.05 to 10 micrograms/kg/hour. Blood samples were obtained simultaneously with LESP measurements for radioimmunoassay determinations of PP. The lowest dose of PP (0.05 microgram/kg/hour) did not produce an increase in either LES pressure or circulating levels of immunoreactive PP. At all other doses, a significant increase occurred in the LESPs and in plasma PP levels. Infusion of PP at 1.0 microgram/kg/hour produced levels of PP similar to those seen postprandially (300 to 400 pg/ml). After vagotomy, studies were repeated at doses ranging from 1.0 to 5.0 micrograms/kg/hour. Infusion of PP at 1.0 microgram/kg/hour produced PP levels similar to those seen in the prevagotomy period; however, there was no change in LES pressures from the fasting postvagotomy values. Administration of PP at 1.5, 2.0, and 5.0 micrograms/kg/hour did produce slight increases in LESP values, which were significantly less than those observed prevagotomy. These higher doses of PP postvagotomy also produced pharmacologic levels of plasma PP. These results demonstrate that an increase in LESP occurs when exogenous PP is administered at doses that produce physiologic levels of PP in dogs with intact vagi; vagotomy results in a marked attenuation of this response.

Food intake, gastric secretion, and motility as affected by avian pancreatic polypeptide administered centrally in chickens

The effects of intracerebroventricular (ICV) injections of avian pancreatic polypeptide (APP) on food intake, gizzard motility, gastric secretion volume, pH, and pepsin concentration was investigated using 16-20-week-old Single-Comb White Leghorn hens. Birds were stereotaxically cannulated in the right lateral ventricle. In addition, a strain gauge was attached to the gizzard to measure motility and a polyethylene cannula was implanted into the caudoventral margin of the proventriculus to collect glandular secretions. All birds were fasted for 18 hr prior to the injection of APP. In Experiment 1 food was made available immediately following the injection of APP while in Experiment 2 food was withheld for an additional one hr post-injection. The ICV injection of APP significantly increased food intake but had no significant effect on gizzard motility, gastric secretion volume, pH, or pepsin concentration in birds given access to food immediately after injection. In birds which remained fasted after injection, pepsin concentration was decreased by APP injection, but gizzard motility, gastric secretion volume, and pH were not affected. Because ICV injections of APP significantly increased food intake and, in fasted birds, decreased pepsin concentration, it appears that APP is involved in the central nervous system control of food intake and pepsin secretion in the domestic fowl.

The effect of neuropeptide Y and peptide YY on electrogenic ion transport in rat intestinal epithelia

1. Neuropeptide Y (NPY), peptide YY (PYY) and, to a lesser extent, human pancreatic polypeptide (HPP) reduced short-circuit current (SCC) in a concentration-dependent manner in epithelial preparations of rat jejunum and descending colon. 2. From concentration-response curves in the jejunum EC50 values of 3 nM for PYY and 10 nM for NPY were obtained. HPP was much less potent, the threshold concentration being around 100 nM, and NPY 13-36 was inactive. 3. Repeated exposure of jejunal preparations to either NPY or PYY led to a rapid desensitization. Cross-desensitization to the actions of these two peptides was also observed. Neither tetrodotoxin (TTX) nor phentolamine affected responses to either NPY or PYY on the jejunum. 4. Responses to both peptides were inhibited by the presence of transport inhibitors, particularly diphenylamine-2-carboxylate (DPC, a chloride channel blocker) and piretanide (Na+-K+-2Cl- co-transport inhibitor). These results may indicate that the reduction in SCC caused by the neuropeptides is due to a net increase in chloride movement in the apical to basolateral direction. 5. 36Cl-flux studies identified an inhibition of chloride secretion as the predominant mechanism of action of NPY and PYY, together with a smaller stimulation of chloride absorption. No significant changes in the movement of 22Na were seen in either direction. 6. The cyclo-oxygenase inhibitors piroxicam (5 microM) and indomethacin (5 microM) significantly reduced the responses to both NPY and PYY in rat jejunum. From this and other evidence it was concluded that the peptides depended for their effect on the endogenous formation of eicosanoids, the prevention of which attenuated the SCC reduction due to the peptides.

Peptide YY antagonizes beta-adrenergic-stimulated release of insulin in dogs

Peptide YY (PYY) and neuropeptide Y (NPY) are peptides of 36 amino acids that share structural homologies with pancreatic polypeptide (PP). PP is predominantly found in the endocrine pancreas. PPY is primarily found in mucosal endocrine cells of the distal ileum, colon, and rectum, whereas NPY is found in both the peripheral and central nervous systems. Previous studies indicate that these peptides can interact with the autonomic nervous system. The objective of the present experiments was to study the effect of PYY on neurally stimulated insulin release [i.e., in response to 2-deoxy-D-glucose (2-DG), a nonmetabolizable glucose analogue] in conscious dogs. Intravenous administration of PYY (100, 200, and 400 pmol.kg-1.h-1) reduced 2-DG-stimulated insulin release in a dose-dependent manner (P less than 0.05) without affecting plasma glucose levels. Administration of NPY (800 pmol.kg-1.h-1), but not PP (400 pmol.kg-1.h-1), reduced 2-DG-stimulated release of insulin (P less than 0.05). The inhibitory action of PYY on 2-DG-stimulated insulin release persisted in the presence of atropine or phentolamine treatment; however, hexamethonium alone or phentolamine plus propranolol treatment blocked the inhibitory action of PYY. Release of insulin stimulated by the beta-agonist isoproterenol was also inhibited by PYY (P less than 0.05). These results indicate that PYY can inhibit autonomic neurotransmission by a mechanism that may involve ganglionic or postganglionic inhibition of beta-adrenergic stimulation. Our findings suggest a role for PYY and NPY in the autonomic regulation of insulin release.

Effects of vasoactive intestinal peptide on steroid secretion and plasminogen activator activity in granulosa cells of the hen

Studies were conducted to evaluate the effects of vasoactive intestinal peptide (VIP) on steroidogenesis and plasminogen-activator (PA) activity in isolated granulosa cells of the largest preovulatory (F1) follicle of the hen. Vasoactive intestinal peptide, but not avian pancreatic polypeptide, the chicken VIP fragment (16-28) or the VIP congener, PHM-27, induced a dose-related increase in progesterone and androgen secretion, with an apparent median effective dose (ED50) of 5.9 X 10(-7) and 5.7 X 10(-7) M, respectively. The effects of VIP were, at least in part, mediated by the adenylyl cyclase system in that cotreatment of cells with VIP and the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), potentiated the steroidogenic effects. However, the time course of action for VIP on steroidogenesis was considerably slower than that for the gonadotropin, luteinizing hormone (LH), and this was attributed to a slower induction of cyclic adenosine 3',5'-monophosphate (cAMP) formation within granulosa cells. Finally, VIP was found to be a potent inhibitor of PA activity, and this inhibition was potentiated by coincubation of VIP with IBMX. We suggest that, in the hen, VIP has a direct and specific action on both steroidogenesis and PA activity, and that these actions are mediated, at least in part, by the adenylyl cyclase system. The comparatively slow induction of cAMP formation by VIP suggests that this peptide is involved in the control of cell differentiation and development rather than the ovulatory process.

Effects of somatostatin and pancreatic polypeptide on exocrine and endocrine pancreas in the rats

The effects of somatostatin-14 (SS) and rat pancreatic polypeptide (rPP) on endocrine and exocrine functions of the pancreas, stimulated by 40 ng/kg cholecystokinin octapeptide during continuous infusion of 1 U/kg/h secretin, were investigated in the rat, in vivo. Protein output in the pancreatic juice and integrated insulin (IRI) secretion were inhibited, in a dose related fashion, by continuous infusion of SS, in doses of 0.5, 5 and 50 micrograms/100g/h. On the other hand, bicarbonate and volume output were not inhibited by SS. The rPP significantly inhibited not only the protein output but also the bicarbonate and volume output of the pancreatic juice in doses of 0.1 and 1 microgram/100g/h. Integrated IRI secretion was inhibited significantly by rPP, but the inhibition of IRI secretion was much greater in the portal than in the jugular vein. Plasma SS and rPP concentrations showed physiological ranges during infusion of doses of 0.5 and 0.1 microgram/100g/h of SS and rPP, respectively. Therefore, there was a marked difference between the inhibition by rPP and that by SS on the exocrine and endocrine pancreas. These observations suggest that SS and PP may play a physiological role in the pancreas and that their effects on the pancreas relate to different mechanisms.

Influence of avian pancreatic polypeptide on pancreatic and biliary secretion in laying hens

White Leghorn hens, 14 to 29 wk of age, were surgically prepared with cannulae for collecting secretions from the cystic duct and the duct draining the ventral pancreatic lobe and for infusing the jugular vein with avian pancreatic polypeptide (aPP) or saline. A plasma infusion rate that produced a plasma level of 15 ng of aPP/mL was used. A comparison of values obtained during saline infusion with those obtained during aPP infusion indicated that pancreatic and biliary secretory volumes and pancreatic total protein concentration were significantly depressed by aPP. The pH of pancreatic and biliary secretions were not significantly affected by aPP. Because aPP also depresses gastric secretion and motility in hens, it is proposed that its physiological role may be to oppose or modulate the actions of other, stimulatory gastrointestinal hormones.

Effects of human pancreatic polypeptide on exocrine pancreatic function in conscious rats

The effect of newly synthesized human pancreatic polypeptide (hPP) on pancreatic secretion stimulated by a diversion of bile-pancreatic juice (BPJ) from the intestine, and plasma hPP concentration were examined in conscious rats. Exogenous hPP infusion (1, 10 micrograms/kg/hr) inhibited pancreatic protein, bicarbonate and fluid outputs during BPJ diversion in a dose-dependent manner. During 1 and 10 micrograms/kg/hr hPP infusion plasma hPP immunoreactivity increased to 369 +/- 22.9 and 1,125 +/- 90.2 pg/ml, respectively. These results suggest that newly synthesized hPP has an inhibitory activity on exocrine function of the pancreas.

Pancreatic polypeptide inhibits pancreatic enzyme secretion via a cholinergic pathway

In rat pancreatic slices, rat pancreatic polypeptide (PP) or C-terminal hexapeptide of PP [PP-(31-36)] inhibited potassium-stimulated amylase release in a dose-dependent manner. The inhibition was unaffected by addition of hexamethonium but blocked by atropine. In contrast, PP(31-36) did not have any effect on acetylcholine- or cholecystokinin octapeptide-stimulated amylase release. In addition, when pancreatic slices were incubated with [3H] choline, PP(31-36) inhibited the potassium-evoked release of synthesized [3H] acetylcholine in a dose-dependent manner. The inhibitory action of PP was unaffected by adrenergic, dopaminergic, or opioid receptor antagonists. Thus PP inhibits pancreatic enzyme secretion via presynaptic modulation of acetylcholine release. This newly identified pathway provides a novel mechanism for hormonal inhibition of pancreatic enzyme secretion via modulation of the classic neurotransmitter function.

Biological actions of peptide YY: effects on endocrine pancreas, pituitary-adrenal axis, and plasma catecholamine concentrations in the dog

The present study was designed to gather information on the biological activity of peptide YY (PYY) in conscious dogs. PYY was infused intravenously at a dose of 238 pmol/kg X h, and plasma concentrations of glucose, insulin, pancreatic polypeptide (PP), ACTH, cortisol and catecholamines (norepinephrine-NE; epinephrine-E; dopamine-DA) were subsequently measured. PYY significantly increased plasma insulin levels transiently without effect on plasma glucose, but decreased plasma PP levels during all infusion periods. PYY stimulated both plasma ACTH and cortisol secretion, and this action of PYY was also shared by PP, with PP being less potent in ACTH-cortisol release. PYY further elicited specific changes in plasma catecholamine concentrations, i.e. an increase of NE but not of E, which were in contrast to the effects of insulin-induced hypoglycemia. PP failed to alter plasma insulin and catecholamine concentrations. These results suggest that PYY can affect anterior pituitary hormone secretion, sympathetic nervous outflow and pancreatic endocrine activity in addition to its known actions on gastric and pancreatic secretion in the dog.

The effects of adrenergic, opioid and pancreatic polypeptidergic compounds on feeding and other behaviors in neonatal leghorn chicks

The present study examined the effects of intracerebral (IC) administration of pancreatic polypeptide (PP), neuropeptide Y (NPY), norepinephrine (NE), dynorphin and naloxone on food intake in 2-day-old Leghorn chicks. Of the compounds studied, only PP (20 micrograms) and naloxone (10 and 20 micrograms) elevated food intake significantly as compared to saline injections. NPY, a potent orexigenic agent in mammals, did not elevate consumption significantly in a dose-related fashion. This latter finding was attributed to the occurrence of tonic-clonic convulsions following NPY administration. However, for those chicks which did not exhibit behavioral convulsions, food intake appeared to be elevated by 1, 5 and 10 micrograms of NPY. Similarly, NE did not elevate food intake but instead induced sedation and narcolepsy, a behavioral response which could be distinguished from the convulsions observed after NPY. In a separate group of chicks, the effect of NPY on cortical activity was examined. Bipolar electrodes were used to record EEG activity before and after IC injections of saline, NPY or NE. The behavioral convulsions induced by NPY corresponded with an increase in high amplitude sharp-wave activity, which persisted for up to 30 min post-injection. Collectively, these results suggest that the neurochemical substrates for feeding in 2-day-old Leghorn chicks are distinct from those underlying food intake in adult mammals.

Melanotropin release inhibiting activity of neuropeptide Y: structure-activity relationships

We have recently shown that the release of alpha-MSH by the intermediate lobe of the frog pituitary is inhibited by neuropeptide Y (NPY). Using the perifusion technique, we have compared in the present study, the alpha-MSH release inhibiting activities of NPY, various NPY short chain analogues and two other members of the pancreatic polypeptide family, peptide YY (PYY) and avian pancreatic polypeptide (APP). The order of biological potency was NPY greater than NPY[2-36] greater than NPY[16-36] greater than NPY[25-36] greater than NPY[1-15]. Among the two pancreatic polypeptides tested, PYY appeared to be almost as potent as NPY while APP was 6 times less active than NPY. Neither NPY[1-15] nor NPY[16-36] could antagonize the inhibitory effect of NPY on alpha-MSH release. The structure-activity relationship study suggests that the bioactive determinant of NPY is located in the C-terminal part of the molecule.

Effects of neuropeptide Y on LH, FSH and TSH release in male rats

These experiments were undertaken to investigate the effects of systemically administered neuropeptide Y (NPY) on gonadotropin secretion in the intact male rat and to determine whether the effects observed might be mediated by a direct action of NPY alone on the anterior pituitary gland (APG). Subcutaneous administration of 10 micrograms of NPY caused a greater than 2-fold increase in serum luteinizing hormone (LH) concentration at 15 min after injection but was without effect on serum follicle-stimulating hormone (FSH) or thyrotropin-stimulating hormone (TSH) levels. The addition of NPY (final concentrations of 10(-8) to 10(-11) M) or the structurally similar neuropeptide, rat pancreatic polypeptide, to culture medium containing hemi-APG did not alter the release of LH, FSH, or TSH. The results indicate that systemically administered NPY can elevate serum LH concentration in intact male rats. This effect does not appear to be due to NPY acting alone at the level of the APG.

Neuropeptide Y inhibits forskolin-stimulated adenylate cyclase activity in rat hippocampus

Neuropeptide Y inhibited the forskolin-stimulated adenylate cyclase activity in rat hippocampus with the half-maximal effect occurring at 73 nM. The maximal inhibition corresponded to a 17-22% decrease of the control level of enzyme activity. The effect of neuropeptide Y was mimicked by the peptide YY but not by the avian pancreatic polypeptide and required micromolar concentrations of GTP. These results indicate that, in the brain, the inhibition of adenylate cyclase activity constitutes a mechanism by which the receptor for neuropeptide Y transduces its signal.

Pancreatic polypeptide enhances postcontractile gallbladder filling in the prairie dog

The hypothesis that pancreatic polypeptide promotes postcontractile gallbladder filling was tested in the prairie dog model. Fifteen animals underwent laparotomy with catheter placement into the gallbladder, distal common bile duct (vent), and femoral vein. The gallbladder was perfused with [14C]polyethylene glycol labeled lactated Ringer's solution at 0.03 ml/min and vent effluent was collected at 2.5-min intervals. All animals received a 20-min intravenous infusion of cholecystokinin-octapeptide, 2.5 ng/kg X min, immediately followed by 60-min infusions of either lactated Ringer's solution or bovine pancreatic polypeptide (PP), 10 or 50 ng/kg X min. Gallbladder emptying and intragallbladder pressure were similar for all three groups after cholecystokinin-octapeptide. When lactated Ringer's was administered after cholecystokinin-octapeptide, gallbladder filling increased by 15.6% with a minimal change in gallbladder pressure. In contrast, infusion of PP10 resulted in a significant (p less than 0.02) increase in gallbladder filling, 64.1% +/- 17.1%, and a significant (p less than 0.05) decrease in intragallbladder pressure, as compared to controls. Similar findings were noted with PP50. These data indicate that exogenous PP significantly increases gallbladder filling after cholecystokinin-induced gallbladder contraction. This enhanced filling results from gallbladder relaxation as manifested by decreased intraluminal pressure. These findings coupled with the observation that serum PP levels remain elevated for up to 6 h after a meal suggest that PP may play a role in the regulation of postprandial gallbladder filling.

Bovine pancreatic polypeptide as an antagonist of muscarinic cholinergic receptors

In dispersed acini from rat pancreas, it was found that bovine pancreatic polypeptide (BPP) and its C-fragment hexapeptide amide (PP-6), at concentrations of 0.1 and 30 microM, respectively, could significantly inhibit amylase secretion stimulated by carbachol (P less than 0.01 or 0.05, respectively), and this inhibition by BPP was dose dependent. 45Ca outflux induced by carbachol was also inhibited by BPP or PP-6, but they had no effect on cholecystokinin octapeptide- (CCK-8) or A23187-stimulated 45Ca outflux. BPP was also capable of displacing the specific binding of [3H]quinuclidinyl benzilate to its receptors, and it possessed a higher affinity (ki 35 nM) than carbachol (Ki 1.8 microM) in binding with M-receptors. It is concluded from this study that BPP acts as an antagonist of muscarinic cholinergic receptors in rat pancreatic acini. In addition, BPP inhibited the potentiation of amylase secretion caused by the combination of carbachol plus secretin or vasoactive intestinal peptide. This may be a possible explanation of the inhibitory effect of BPP on secretin-induced pancreatic enzyme secretion shown in vivo, since pancreatic enzyme secretion stimulated by secretin under experimental conditions may be the result of potentiation of enzyme release produced by the peptide in combination with a cholinergic stimulant.

Effect of pancreatic polypeptide on the motility of the guinea-pig small intestine in vitro

The effect of porcine pancreatic polypeptide (PP) on the motor activity of the longitudinal and circular muscles of the guinea-pig isolated small intestine was investigated. PP (0.2-20 nM) inhibited cholinergic contractions of the longitudinal muscle in response to electrical field stimulation, the maximal effect being a 30% reduction of the contraction amplitude. Carbachol-induced contractions of the longitudinal muscle were not affected by PP (10 nM). PP (0.3-30 nM) also inhibited reflex contractions of the circular muscle elicited by balloon distension and recorded orally to the site of distension; the maximal effect was a 80% reduction of the reflex contraction. In contrast, carbachol-induced contractions of the circular muscle remained unaltered by PP (10 nM). It was further found that PP (10 and 100 nM) enhanced the threshold intraluminal pressure at which peristaltic waves were triggered. All these effects of PP appeared to be transient. Taken together, these data indicate that PP does not act on intestinal smooth muscle but can modulate the activity of certain enteric neurones which are involved in the regulation of intestinal motility.

A hormonal mechanism for the interdigestive pancreatic secretion in dogs

We investigated a hormonal mechanism involved with cyclic pancreatic secretion in interdigestive state in four dogs prepared with gastric and modified Herrera's pancreatic cannulas and four dogs prepared with gastric and Thomas' duodenal cannulas. Cholecystokinin-pancreozymin (CCK-PZ), secretin, pancreatic polypeptide (PP), and motilin were considered as candidate hormones that might be involved in the mechanism. Radioimmunoassays of the four hormones in serial plasma samples showed cyclic increases in only two hormones including motilin and PP, which coincided with the cyclic increase in pancreatic secretion. However, only motilin given intravenously produced a cyclic pancreatic secretion similar to spontaneous cyclic pancreatic secretion in interdigestive state. Although the magnitude of peak pancreatic secretion was not altered during intravenous infusion of motilin in doses of 0.06 microgram X kg-1 X h-1 or 0.06 microgram/kg, the peak secretion occurred more frequently than that during the control interdigestive state. Atropine administered intravenously abolished the cyclic increases in both plasma motilin concentration and pancreatic secretion. Exogenous secretin, CCK-PZ8 and PP failed to produce cyclic pancreatic secretion. To further elucidate the mechanism involved, the effect of intravenous infusion of a rabbit anti-CCK-PZ or antimotilin serum on the cyclic pancreatic secretion was studied. The antimotilin serum completely blocked the pancreatic secretory cycles in two dogs so studied, whereas rabbit anti-CCK-PZ serum did not influence the pancreatic cycle in two dogs. We conclude that circulating motilin plays an important role on the development of cyclic increase in the pancreatic secretion in two dogs so studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptidergic modulation of the membrane potential of the Schwann cell of the squid giant nerve fibre

The effects of a range of neuropeptides were investigated on the membrane potential of the Schwann cells of the giant nerve fibre of the tropical squid. Vasoactive intestinal peptide (VIP) produced a dose-dependent, long-lasting hyperpolarization of the Schwann-cell membrane potential. Among peptides structurally related to VIP, similar effects were produced by peptide histidine isoleucine (PHI) but not by secretin and glucagon. Substance P and somatostatin also hyperpolarized the Schwann-cell membrane potential but via receptor systems distinct from those activated by VIP. Methionine enkephalin ([Met]-enkephalin) blocked the actions of all the above peptides as well as the effects of DL-octopamine and carbachol. The actions of [Met]-enkephalin upon the VIP responses were antagonized by naloxone. VIP produces its effects on the Schwann-cell membrane potential via a receptor system that is independent from those described previously which mediate the effects of carbachol and DL-octopamine. However, VIP can potentiate the effects of the latter systems. The actions of VIP on the Schwann cell are unlikely to be mediated via changes in adenosine 3',5'-cyclic monophosphate (cyclic AMP) levels and are insensitive to changes in the level of extracellular calcium in the superfusate. The actions of VIP are, however, potentiated in the presence of low concentrations of lithium ions suggesting that the VIP receptor may mediate its effects by inducing the hydrolysis of polyphosphatidylinositols in the Schwann-cell membrane. Evidence is presented for the existence of an endogenous VIP-like component in the normal hyperpolarizing action of giant-axon activity on the membrane potential of the Schwann cell.

Neuropeptide Y and pancreatic polypeptide: effects on thyroid hormone secretion in the mouse

Neuropeptide Y (NPY) is known to occur in adrenergic nerves within the thyroid gland and may thus be released concomitantly with noradrenaline upon adrenergic activation. In this study, the effects of combined administration of NPY and noradrenaline on thyroid hormone secretion were investigated under in vivo conditions in the mouse. Mice were pretreated with radioiodine and thyroxine: the subsequent release of radioiodine into blood upon stimulation is a reflection of the release of thyroid hormones since more than 90% of the released radioiodine is in the form of thyroid hormones. It was found that TSH enhanced the radioiodine levels in blood to 197 +/- 8% (P less than 0.01). Noradrenaline inhibited the TSH-induced thyroid hormone secretion to 168 +/- 6% (P less than 0.01), and NPY potentiated this inhibitory action of noradrenaline (P less than 0.01): the TSH-induced thyroid hormone secretion was only 19 +/- 6% after administration of both noradrenaline and NPY. Furthermore, alpha-adrenoceptor blockade by phentolamine abolished the effect of noradrenaline on TSH-induced thyroid hormone secretion and, during alpha-adrenoceptor blockade, NPY potentiated the secretory response to TSH. To study the specificity of the effects exerted by NPY, the influences of avian pancreatic polypeptide (APP) and bovine pancreatic polypeptide (BPP), which both show structural similarities to NPY, were also studied. However, in contrast to NPY, neither APP nor BPP had any effects on TSH-stimulated thyroid hormone secretion. Interestingly, an inhibitory action on non-stimulated radioiodine release (= TSH-independent thyroid hormone secretion) was seen in response to APP and BPP. This effect was not exerted by NPY.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of rabbit anti-pancreatic polypeptide serum on postprandial pancreatic exocrine secretion in dogs

To determine whether pancreatic polypeptide (PP) is a physiologic inhibitor of pancreatic secretion, we have studied the effects of normal rabbit serum and anti-PP serum on pancreatic secretion during infusion of a physiologic dose of PP or intragastric food instillation in dogs. Infusion of 180 pmol/kg X h of PP, previously incubated with normal rabbit serum, induced increases in plasma PP (220 +/- 21 pmol/L) similar to those after the meal (213 +/- 51 pmol/L) and was accompanied by significant inhibition of pancreatic flow rate, bicarbonate output, and protein output (p less than 0.05) stimulated by secretin and cholecystokinin (n = 6). However, when the effect of exogenous PP was studied after in vivo administration of anti-PP serum or after previous in vitro incubation with anti-PP serum, no inhibition of pancreatic secretion was found, indicating that immunoneutralization of PP blocks the biologic activity of the hormone. Intragastric instillation of 400 ml of liver extract resulted in significant increases in pancreatic flow rate and outputs of protein and bicarbonate (p less than 0.01; n = 8), both during administration of normal rabbit serum and anti-PP serum. The postprandial increase in pancreatic secretion during administration of anti-PP serum was not significantly different from that during administration of normal rabbit serum. We, therefore, conclude that PP is not a physiologic inhibitor of postprandial pancreatic secretion.

Relationships between duodenal motility and pancreatic secretion in fasted and fed dogs

A relationship between duodenal myoelectric or motor activity and exocrine pancreatic secretion as well as plasma gut hormone levels has been investigated in fasted dogs, fed dogs, and dogs that were stimulated with exogenous gut hormones. Pancreatic secretion showed typical periodicity in phase with the myoelectric or motor activity of the duodenum. Fasting pancreatic bicarbonate and protein secretion reached peaks during phase III of the interdigestive migrating motor complex (MMC) cycle that were significantly larger than nadir levels occurring during phase I of the cycle. These fasting bicarbonate and protein peaks reached, respectively, approximately 9 and 30% of the highest postprandial outputs and 4 and 14% of the maximal secretory capacity elicited by secretin or CCK. They were accompanied by a significant rise in plasma motilin, gastrin, and pancreatic polypeptide (PP), but only exogenous motilin given in physiological dose induced motility pattern and pancreatic secretion similar to those observed during phase III. Feeding interrupted both motor and secretory MMC cycle, increased the pancreatic secretion to approximately 40-60% of the maximal secretory capacity, and was accompanied by increments in plasma gastrin, cholecystokinin (CCK), secretin, and PP. None of these hormones applied alone in physiological dose was capable of reproducing the postprandial inhibition of MMC cycles. We conclude that the pancreatic secretion in fasted dogs fluctuates periodically in phase with duodenal motility, but the phase III peak secretory outputs represent only minute fractions of the maximal secretory capacity and can therefore be ignored in regular testing of pancreatic secretion.