Effects of peptide YY and its analogues on chloride ion secretion in fed and fasted rat jejunum

The aim of our study was to determine whether a meal modifies the antisecretory response induced by PYY and the structural requirements to elicit antisecretory effects of analogue PYY(22–36) for potential antidiarrhea therapy. The variations in short-circuit current (Isc) due to the modification of ionic transport across the rat intestine were assessed in vitro, using Ussing chambers. In fasted rats, PYY induced a dose- and time-dependent reduction in Isc, with a sensitivity threshold at 5 × 10⁻¹¹ M (ΔIsc −2 ± 0.5 μA/cm²). The reduction was maximal at 10⁻⁷ M (Isc −23 ± 2 μA/cm²), and the concentration producing half-maximal inhibition was 10⁻⁹ M. At 10⁻⁷ M, reduction of Isc by PYY reached 90% of response to 5 × 10⁻⁵ M bumetanide. The PYY effect was partly reversed by 10⁻⁵ M forskolin (Isc +13.43 ± 2.91 μA/h·cm², p < 0.05) or 10⁻³ M dibutyryl adenosine 3′,5′ cyclic monophosphate (Isc +12 ± 1.69 μA/cm², p < 0.05). Naloxone and tetrodotoxin did not alter the effect of PYY. In addition, PYY and its analogue P915 reduced net chloride ion secretion to 2.85 and 2.29 μEq/cm² (p < 0.05), respectively. The antisecretory effect of PYY was accompanied by dose- and time-dependent desensitization when jejunum was prestimulated by a lower dose of peptide. The antisecretory potencies exhibited by PYY analogues required both a C-terminal fragment (22–36) and an aromatic amino acid residue (Trp or Phe) at position 27. At 10⁻⁷ M the biological activity of PYY was lower in fed than fasted rats (p < 0.001). Our results confirm the antisecretory effect of PYY, but show that the fed period is accompanied by desensitization, similar to the transient desensitization observed in the fasted period with cumulative doses. This suggests that PYY may act as a physiological mediator that reduces intestinal secretion.     

Effects of serotonin on the physiology of the rabbit small intestine

Serotonin has been shown to alter the intestinal transport of ions and intestinal motility. These effects may interfere with each other, modulating the whole physiology of the intestine. We have previously shown that serotonin also alters the transport of nutrients. Thus, the aims of the present work were to determine the possible interference between the secretagogue effect of serotonin and the mechanism by which serotonin inhibits the absorption of nutrients, and to study the effect of serotonin on the digestive activity of nutrients of the brush border membrane jejunum enterocyte in the rabbit. The results show that the secretagogue effect of serotonin neither affects the inhibitory effect of serotonin on the intestinal absorption of the nutrients, nor affects the activity of Na+/K+-ATPase. The activity of sucrase and aminopeptidase N was also not affected by serotonin in the rabbit jejunum. Finally, we also studied different parameters of the motility in the rabbit small intestine. Serotonin seemed to stimulate the motility of the rabbit small intestine by increasing integrated mechanical activity and tone of muscle fibers in duodenum, jejunum, and ileum. In conclusion, serotonin might alter or modulate the whole intestinal physiology.     

Effects of peptide YY on intestinal blood flow distribution and motility in the dog

Previous investigators in our laboratory have demonstrated that peptide YY (PYY), a putative gut hormone, exerts a potent emetic effect when administered intravenously to conscious dogs. The current study was carried out to examine the effects of an emetic dose of PYY on cardiovascular status, splanchnic blood flow distribution (estimated using 15 micron microspheres) and small intestinal motility in anesthetized dogs. PYY, infused i.v. at a dose of 25 pmol/kg/min led to a localized significant reduction in small intestinal muscularis externa blood flow both 15 and 30 min after the start of PYY infusion in both jejunum and ileum. This decreased muscularis perfusion was not accompanied by any significant change in whole gut wall blood flow and was explained on the basis of an observed significant redistribution of blood flow away from the muscularis towards the mucosa/submucosa. Similar, although non-significant, effects of PYY on colonic blood flow distribution were also observed. Despite the effects on jejunum and ileum, PYY exerted minimal effects on duodenal blood flow. The decrease in ileal and jejunal muscularis blood flows was accompanied by a significant increase in the amplitude of intestinal contractions in these regions. Frequency of contractions was unaltered however. These results demonstrate that PYY infusion leads to concurrent changes in small intestinal blood flow and motility.     

Distribution of pancreatic polypeptide and peptide YY

The cellular distribution of PP and PYY in mammals is reviewed. Expression of PP is restricted to endocrine cells mainly present in the pancreas predominantly in the duodenal portion (head) but also found in small numbers in the gastro-intestinal tract. PYY has a dual expression in both endocrine cells and neurons. PYY expressing endocrine cells occur all along the gastrointestinal tract and are frequent in the distal portion. Islet cells expressing PYY are found in many species. In rodents they predominate in the splenic portion (tail) of the pancreas. A limited expression of PYY is found also in endocrine cells in the adrenal gland, respiratory tract and pituitary. Peripheral, particularly enteric, neurons also express PYY as does a restricted set of central neurons.     

Cholecystokinin and peptide YY are released by fat in either proximal or distal small intestine in dogs

We tested the hypothesis that the release of cholecystokinin (CCK) and peptide YY (PYY) may be independent of the region of the small intestine exposed to fat. In five dogs equipped with duodenal and midgut fistulas, the small intestine was compartmentalized so that fat was confined to either the proximal or distal one-half of the gut. Plasma CCK and PYY levels were measured by radioimmunoassay and compared by the square root of the area under the curve (sqrt AUC), representing the plasma peptide concentration over time. CCK was released similarly whether fat was delivered into the proximal (69.9+/-4.7 pM) or distal (71.0+/-5.5 pM) gut, but significantly more CCK (88.9+/-5.6 pM; p<0.05) was released when both the proximal and distal gut were perfused simultaneously with fat. PYY was released similarly whether fat was delivered into the proximal (34.9+/-2.6 pM) or distal (40.0+/-1.2 pM) gut or both (38.6+/-2.2 pM). We conclude that CCK and PYY are released by fat in either the proximal or distal one-half of the small intestine.     

Ontogeny and the effect of aging on pancreatic polypeptide and peptide YY

Pancreatic polypeptide (PP) and peptide YY (PYY) are related neuroendocrine peptides that are expressed in specialized cells. PP is found around the time of birth in different species. PYY in mice and rats has been extensively studied. PYY is the first peptide hormone to appear in both the pancreas and the colon and is initially expressed together with all other pancreatic islet and gut hormones. This suggests that there is a PYY-producing endocrine progenitor cell, at least in rodents. Whether the same is true for other species is unknown. In chickens, however, pancreatic insulin and glucagon cells appear before PYY. After birth, PYY levels in rats and humans reflect adaptation to enteral feeding. Whereas PYY cells increase with age in rodents, no such changes have been found in humans.     

Effects of glycine-extended and serine13-phosphorylated forms of peptide YY on food intake in rats

The gut hormone peptide YY(3-36)-amide [PYY(3-36)-NH₂] is significantly more potent than PYY(1-36)-NH₂ in reducing food intake in rats and humans. Other Gly-extended and Ser¹³-phosphorylated PYY forms have been detected or predicted based upon known cellular processes of PYY synthesis and modification. Here we compared the effects of 3-h IV infusion of PYY(1-36)-NH₂, PYY(3-36)-NH₂, PYY(1-36)-Gly-OH, PYY(3-36)-Gly-OH, Ser¹³(PO₃)-PYY(1-36)-NH₂, Ser¹³(PO₃)-PYY(3-36)-NH₂, Ser¹³(PO₃)-PYY(1-36)-Gly-OH, and Ser¹³(PO₃)-PYY(3-36)-Gly-OH during the early dark period on food intake in freely feeding rats. PYY(3-36)-NH₂ and Ser¹³(PO₃)-PYY(3-36)-NH₂ reduced food intake similarly at 50 pmol/kg/min, while only PYY(3-36)-NH₂ reduced food intake at 15 pmol/kg/min. PYY(1-36)-NH₂ and Ser¹³(PO₃)-PYY(1-36)-NH₂ reduced food intake similarly at 50 and 150 pmol/kg/min. In contrast, PYY(1-36)-Gly-OH, PYY(3-36)-Gly-OH, Ser¹³(PO₃)-PYY(3-36)-Gly-OH, and Ser¹³(PO₃)-PYY(1-36)-Gly-OH had no effect on food intake at doses of 50 or 150 pmol/kg/min. Taken together, these results indicate that (i) PYY(3-36)-NH₂ is significantly more potent than PYY(1-36)-NH₂ in reducing food intake, (ii) Gly-extended forms of PYY are significantly less potent than non-extended forms, and (iii) Ser¹³-phosphorylation of PYY(3-36)-NH₂ decreases the anorexigenic potency PYY(3-36)-NH₂, but not PYY(1-36)-NH₂. Thus, PYY(3-36)-NH₂ appears to be the most potent PYY form for reducing food intake in rats.     

Identification and characterization of the emetic effects of peptide YY

Emesis was noted following intravenous bolus injections into dogs of a chromatographic subfraction derived from porcine small intestinal tissue extracts. The active agent was isolated from this subfraction using sequential ion-exchange and reverse-phase HPLC and demonstrated to be the recently identified regulatory peptide PYY. The threshold dose for PYY-induced emesis in the dog is less than 120 pmol/kg. Emesis was sometimes seen following large IV bolus doses of neuropeptide Y (NPY), but none was seen following IV injection of pancreatic polypeptide (PP). Dogs prepared with discrete, bilateral lesions of the area postrema were refractory to a suprathreshold emetic dose of PYY. PYY is the most potent, circulating emetic peptide identified to date.     

Isolation and primary structure of human peptide YY

The isolation, primary structure and chemical synthesis of human peptide YY (PYY) are described. The peptide was purified from human colonic extracts using a chemical method which detected the C-terminal tyrosine amide structure of PYY. Human PYY consists of 36 amino acid residues and the complete amino acid sequence is: Tyr-Pro-Ile-Lys-Pro-Glu-Ala-Pro-Gly-Glu- Asp-Ala-Ser-Pro-Glu-Glu-Leu-Asn-Arg-Tyr-Tyr-Ala-Ser-Leu-Arg-His-Tyr-Leu- Asn-Leu-Val-Thr-Arg-Gln-Arg-Tyr-NH2. The differences between the structures of porcine and human PYY are at positions 3 (Ala/Ile replacement) and 18 (Ser/Asn). Synthetic human PYY prepared using a solid-phase synthetic technique was found to be structurally identical to the natural peptide.     

Antiobesity and emetic effects of a short-length peptide YY analog and its PEGylated and alkylated derivatives

Neuropeptide Y2 receptor (Y2R) agonism is an important anorectic signal and a target of antiobesity drug discovery. Recently, we synthesized a short-length Y2R agonist, PYY-1119 (4-imidazolecarbonyl-[d-Hyp²⁴,Iva²⁵,Pya(4)²⁶,Cha^27,36,γMeLeu²⁸,Lys³⁰,Aib³¹]PYY(23–36), 1) as an antiobesity drug candidate. Compound 1 induced marked body weight loss in diet-induced obese (DIO) mice; however, 1 also induced severe vomiting in dogs at a lower dose than the minimum effective dose administered to DIO mice. The rapid absorption of 1 after subcutaneous administration caused the severe vomiting. Polyethylene glycol (PEG)- and alkyl-modified derivatives of 1 were synthesized to develop Y2R agonists with improved pharmacokinetic profiles, i.e., lower maximum plasma concentration (C_max) and longer time at maximum concentration (T_max). Compounds 5 and 10, modified with 20?kDa PEG at the N-terminus and eicosanedioic acid at the Lys³⁰ side chain of 1, respectively, showed high Y2R binding affinity and induced significant body weight reduction upon once-daily administration to DIO mice. Compounds 5 and 10, with their relatively low C_max and long T_max, partially attenuated emesis in dogs compared with 1. These results indicate that optimization of pharmacokinetic properties of Y2R agonists is an effective strategy to alleviate emesis induced by Y2R agonism.     

Neuropeptide Y and peptide YY neuronal and endocrine systems

An extensive system of neuropeptide Y (NPY) containing neurons has recently been identified in the central and peripheral nervous system. In addition, NPY and a structurally related peptide, peptide YY (PYY), containing endocrine cells have been identified in the periphery. The NPY system is of particular interest as the peptide coexists with catecholamines in the central and sympathetic nervous system and adrenal medulla. Evidence has been presented which indicates that NPY may play important roles in regulating autonomic function.     

Feedback regulation of pancreatic secretion by peptide YY

The present status of our understanding of the feedback regulation of pancreatic secretion by peptide YY (PYY) released from the distal intestine is reviewed. Exocrine pancreatic secretion is primarily controlled by the cephalic (the vagus nerve), gastric (acid and pepsin secretion, and nutrients delivered into the duodenum by gastric emptying), and intestinal (secretin and CCK) mechanisms. PYY acts on the multiple sites in the brain and gut, and inhibits pancreatic secretion by regulating these primary control mechanisms. The involvement of Y(1) and Y(2) receptors has been suggested in the regulation of pancreatic secretion. However, it remains to be studied which site of action or receptor subtype is physiologically most important for this regulation.     

Multiple regulation of peptide YY secretion in the digestive tract

In the last two decades, multiple aspects of the peptide YY (PYY) secretion have been investigated. Besides fat and fatty acids, many luminal nutrients in the distal intestine appear to induce PYY release. Some studies have shown that bile acid, but not nutrients, plays a crucial role in the regulation of PYY secretion. Moreover, chyme in the proximal intestine also regulates the peptide release by indirect action through humoral and neuronal factors. Gastrin, cholecystokinin, and the vagus nerve are major candidates for mediators of these indirect actions. Several growth factors have been shown to regulate PYY synthesis in mucosa of the distal intestine. This review is aimed at presenting an overview of these recent studies on PYY secretion in the distal intestine.     

Effects of peptide YY(3-36) on PRL secretion: pituitary and extra-pituitary actions in the rat

Polypeptide YY(3-36) (PYY(3-36)) is a gastrointestinal secreted molecule, agonist of neuropeptide Y (NPY) receptor subtypes Y2 and Y5, that has been recently involved as anorexigenic signal in the network controlling food intake. Notably, several factors primarily involved in food intake control and energy homeostasis (as leptin, orexins, ghrelin and NPY) have been linked also to the regulation of anterior pituitary hormone secretion and carry out pleiotropic effects upon the reproductive axis. However, whether similar actions are conducted by PYY(3-36) remains so far largely unexplored. Present studies were undertaken to analyze the potential effects of PYY(3-36) in the control of prolactin (PRL) secretion in the rat. To this end, responses to PYY(3-36) in terms of PRL secretion were monitored in vitro, after pituitary exposure to 10(-8) to 10(-6) M concentrations, and in vivo, after i.p. administration of different doses of PYY(3-36) (3, 10 and 30 microg/kg) to prepubertal male and female rats. In addition, the in vivo effects of PYY(3-36) were tested after central (i.c.v.) administration of 3 nmol of the peptide to prepubertal rats, and in hyperprolactinaemic aged females. PYY(3-36) stimulated, in a dose-dependent manner, in vitro PRL secretion by pituitaries from prepubertal male and female rats. In contrast, systemic administration of PYY(3-36) failed to modify serum PRL levels, whereas central infusion of PYY(3-36) significantly inhibited PRL secretion in prepubertal rats. Finally, PRL secretion was stimulated in aged hyperprolactinaemic female rats by systemic administration of PYY(3-36). In conclusion, the anorexigenic peptide PYY(3-36) may participate in the control of PRL secretion in the prepubertal rat, acting at pituitary (stimulatory effect) and extra-pituitary (likely inhibitory action at the hypothalamus) sites of the lactotrope axis. Moreover, net actions of PYY(3-36) on PRL secretion may depend on the age and prevailing PRL levels.     

Peptide YY induces nerve-mediated responses in the guinea pig intestine.

The actions of peptide YY (PYY) were studied in longitudinal organ-bath preparations of the guinea pig intestine. PYY induced concentration-dependent (10(-9)-5 x 10(-8) M) relaxations of tissue from the duodenum, jejunum, ileum, and colon. These responses were unaffected by adrenergic blockade and atropine treatment but could be prevented by tetrodotoxin. The pharmacology of PYY actions in segments of the small and large intestine indicated the involvement of intrinsic nonadrenergic, noncholinergic inhibitory neurones in the relaxation response to this peptide. All tissues could be made tachyphylactic to PYY without affecting their ability to respond to the direct acting muscle relaxants ATP or papaverine. Moreover, nicotinic ganglion stimulated relaxations and cholinergic nerve-mediated contractions were also unaffected. These results show applied PYY to have potent neurogenic actions in the guinea pig intestine with some similarities to PYY actions in the rat intestine.     

Isolation and sequence of rat peptide YY and neuropeptide Y

Rat peptide YY and rat neuropeptide Y have been isolated in parallel from colon and brain extracts respectively, using salt fractionation, gel filtration chromatography, cation-exchange HPLC, and reverse phase phenyl-silica HPLC. Immunoreactivity was identified using a combination of 3 NPY immunoassays which exhibit differing cross-reactivities for PYY (90%, less than 0.01% and 30% respectively). The yield at the final purification step was 1.2 nmol rPYY and 0.5 nmol rNPY. Half of each purified peptide was subjected to complete microsequence analysis. This showed that while rat NPY was structurally identical to human NPY, the sequence of PYY from rat colon was the same as porcine PYY isolated from extracts of duodenum.     

Regional distribution and plasma concentration of peptide YY in sheep

Peptide YY (PYY)-positive cells are distributed in the mucosa of the ileum, cecum, colon, and rectum of sheep, but not in other layers of these regions. By radioimmunoassay, mucosal content of PYY in the ovine large intestine was much less than that in the rat intestine. The plasma concentration of immunoreactive PYY did not significantly fluctuate over a 48-h period in conscious sheep, even after ingestion of roughage and concentrate. Intraluminal nutrients into the ileum and i.v. CCK8 also did not raise the plasma level of PYY. Therefore, PYY seems unlikely to play a role as "ileal brake" in sheep.     

Cellular localization, half-life, and secretion of peptide YY

Tissue and plasma concentration of peptide YY (PYY) were measured by means of a radioimmunoassay (RIA) developed in our laboratory, using a specific PYY antiserum generated in New Zealand white rabbits against synthetic PYY, and dextran-coated charcoal to terminate the assay. Cellular localization of PYY was studied immunohistochemically using the peroxidase-antiperoxidase (PAP) technique. The highest tissue concentration of PYY was found in the mucosa of the terminal ileum and colon. PYY-containing secretory granules were primarily found in the basal pole of open-type endocrine cells. Basal plasma concentration of PYY was 70 +/- 9 pg/ml and rose to 357 +/- 30 pg/ml during the IV administration of PYY at 400 pmol/kg-h. A significant correlation was found (r = 0.94, p less than 0.05) between dose of PYY (12.5, 25, 50, 100, 200, 400 pmol/kg-h, IV) and plasma concentration of PYY. The calculated half-life of PYY in plasma was 8.3 +/- 1.9 minutes. Plasma concentration of PYY during the intraduodenal administration of sodium oleate (150 +/- 20 pg/ml) or long-chain triglyceride (187 +/- 37 pg/ml) was similar to plasma concentration of PYY obtained during the IV administration of PYY at 100 pmol/kg-h. Plasma concentration of PYY raised (126 +/- 10 pg/ml) after the administration of bombesin (400 pmol/kg-h, IV). Bile enhanced release of PYY. The present study suggests a hormonal role for PYY.     

Effect of angiotensin II and peptide YY on cerebral and circumventricular blood flow

Angiotensin II and peptide YY (PYY) are putative neuro/humoral agents acting at several circumventricular regions. These peptides also constrict cerebral vessels. We examined the effect of acute intravenous infusion of saline, angiotensin II and peptide YY on local cerebral blood flow (14C-iodoantipyrine autoradiography) in the circumventricular and non-circumventricular brain regions of 17 conscious rats. No reductions in brain blood flow (28 regions) were observed although angiotensin II and PYY infusion elevated arterial blood pressure 15-25% without influencing heart rate, suggesting an increase in peripheral resistance. However, local blood flow was dependent on the peptide infused. During PYY infusion, blood flow was rather constant in the 20 non-circumventricular regions examined whereas an increase in blood flow and a slight decrease in cerebrovascular resistance occurred in the circumventricular regions. The area postrema exhibited the most pronounced changes--an elevation in blood flow of 44 +/- 11% and a reduction in resistance of 20 +/- 5% in comparison to that in control animals. During angiotensin II infusion, local cerebral blood flow was similar to that in controls and local cerebrovascular resistance was elevated. Thus, the local cerebral circulatory response to peptide administration was dependent on the location of the region examined (circumventricular or non-circumventricular) and on the vasoactive peptide infused.