Receptors for gut regulatory peptides

VIPoma with expression of both VIP and VPAC1 receptors in a patient with WDHA syndrome

We report a case of VIPoma in a 72-year-old female patient who presented with excessive diarrhea, severe hypokalemia, and acidemia. She had been referred to our hospital three times because of severe diarrhea. No primary tumor site was found by conventional techniques, including contrast-enhanced CT and MRI, angiography, endoscopy, and positron emission tomography (PET), but a tumor was subsequently found in the head of the pancreas by octreotide scanning. Her diarrhea diminished dramatically after octreotide treatment, while her diarrhea has ceased without the therapy of octreotide at the first admission in the course of 2 years of her disease. Immunohistochemial analysis of the excised tumor tissue revealed the expression of both vasoactive intestinal peptide (VIP) and VIP and pituitary adenylate cyclase-activating peptide 1 (VPAC1) receptors. This is the first case report of a VIPoma that immunostains for VIP and VPAC1 receptors and indicates that abundant VIP produced by VIPoma might inhibit its growth and reduce VIP secretion via the VPAC1 receptor in vivo.

Postnatal - physiological research of the bronchial receptor system development on the isolated preparation of the human trachea in vitro

Research was done on pharmacological-physiological development of the bronchial receptor system on the smooth muscles of trachea in the newborn children, alive-born and stillborn children. Monitored was the response on: acetylcholine, dopamine, histamine and serotonin in different molar concentrations 10(-4), 10(-3), 10(-2), 10 mol/dm(-3), micromol/dm(-3)). Research was done on tonus of tracheal smooth muscles of 23 tracheal preparations taken by autopsy after death from different factors. Based on pharmacological-physiological research on the preparations of human isolated trachea it was find out that: acetylcholine stimulation effect is significant (p>0,01) in 38-41 weeks of pregnancy comparing with that in 30-37 weeks of pregnancy (p>0,01), while dopamine stimulation effect is significant (p>0,05) in 30-37 pregnancy weeks comparing with the effect of acetylcholine and dopamine on the still-born infants of the same pregnancy period (p<0,01). Histaminic receptors were developed during intrauterine life after 38 weeks of pregnancy (p>0,025). Serotonin has caused contraction of the bronchial smooth muscles after 30 pregnancy weeks, but response was not significant (p<0,01). This suggests that cholinergic and adrenergic system of the airways in alive newborn infants develops in parallel intrauterine, contrary to other systems which develop in certain extrauterine life phases.

Diagnosis and treatment of VIPoma in a female patient

We report a case of VIPoma in an 83-year-old female patient, who presented with frequent and excessive diarrhoea, muscle weakness, and severe hypokalaemia. Abdominal computed tomography (CT) revealed a 4x6 cm mass in the body of the pancreas. Laboratory analysis showed elevated levels of both vasoactive intestinal polypeptide (VIP; 153 pmol/l) and pancreatic polypeptide (161 pmol/l). In view of the patient's age, physical condition, and tumour size, surgical resection was not performed. The patient was treated with a long-acting octreotide, after which her symptoms diminished. After 24 months of follow-up, the patient remained in good physical condition without any further serious gastrointestinal symptoms. The VIPoma syndrome is caused by a neuroendocrine tumour, usually located in the pancreas, which secretes VIP, causing severe diarrhoea, dehydration and hypokalaemia. Treatment options include resection of the tumour, chemotherapy or the reduction of symptoms with somatostatin analogues. We provide an overview of the incidence, pathophysiology, diagnosis, treatment strategies, and prognosis of this rare syndrome.

Therapeutic potential of CRF receptor antagonists: a gut-brain perspective

Activation of the corticotropin-releasing factor (CRF) family of neuropeptide receptors in the brain and periphery appears to mediate stress-related changes in a variety of physiological and functional domains. Comparative pharmacology of CRF receptor agonists suggests that CRF, urocortin, sauvagine and urotensin consistently mimic, and conversely peptide CRF receptor antagonists lessen, the functional consequences of stressor exposure. Together with the development of novel non-peptide CRF receptor antagonists, a growing number of CRF receptor selective ligands are available to elucidate the neurobiology and physiological role of CRF systems. The present review considers available preclinical evidence as well as results from one Phase II clinical trial which address the hypothesis that CRF receptor antagonists may represent a new option for pharmacotherapy of stress-related disorders.

Neural mediation of vasoactive intestinal polypeptide inhibitory effect on jejunal alanine absorption

It was recently shown that vasoactive intestinal polypeptide (VIP) inhibits rat jejunal alanine absorption, an effect that was significantly reduced by vagotomy. This study assesses the role of capsaicin-sensitive primary afferents (CSPA) and the myenteric plexus in the inhibition of rat jejunal alanine absorption by VIP. Continuous intravenous infusion of VIP (11.2 ng . kg-1 . min-1) reduced alanine absorption by 60% in sham control rats and by 20% in rats neonatally treated with capsaicin (P < 0.01). In in vitro experiments, VIP decreased alanine uptake by jejunal strips isolated from sham control rats in a dose-dependent manner. In the presence of 40 nM VIP, alanine uptake by full-thickness jejunal strips was reduced by 54% in sham control rats and by 25% in rats neonatally treated with capsaicin (P < 0.001). On the other hand, VIP reduced alanine uptake by mucosal scrapings by 25% in sham rats compared with 9% reduction in neonatally treated rats. Chemical ablation of the extrinsic innervation and jejunal myenteric plexuses by pretreatment with benzalkonium chloride significantly (P < 0.001) reduced basal alanine absorption and the inhibitory effect of VIP. Moreover, incubation of intestinal strips with tetrodotoxin and atropine reduced significantly (P < 0.05) the inhibitory effect of VIP on alanine absorption. These data suggest that VIP exerts its inhibitory effect on alanine absorption through the CSPA fibers and the myenteric plexus. The neuronal circuitry of this inhibitory process may involve cholinergic muscarinic mechanisms.

Identification and distribution of mRNA encoding the Y1, Y2, Y4, and Y5 receptors for peptides of the PP-fold family in the rat intestine and colon

Peptide YY (PYY), neuropeptide Y (NPY) and pancreatic polypeptide (PP) are structurally related peptides which have potent antisecretory effects in small and/or large intestines. Receptors mediating these effects are still unknown with the exception of a PYY-preferring receptor expressed in small intestinal crypts. In the present study, expression of recently cloned Y1, Y2, and Y5 receptors which have similar affinity for PYY and NPY and Y4 receptors which have a high affinity for PP was investigated in gut by RT-PCR analysis. The data show that all Y receptors are expressed in small intestine and/or colon but with specific distributions. Y1 receptors are only expressed in nonepithelial colonic tissue, whereas Y2 and Y4 receptors are present in both epithelial and nonepithelial tissue of the small or large intestine. In contrast, Y5 receptor expression appears to be restricted to epithelial crypts of the small intestine and nonepithelial tissue of colon. Sequencing of PCR products showed 100% identity with the corresponding sequences of the cloned Y1, Y4, or Y5 receptors. The PCR product obtained with Y2 primers from rat crypt cells showed 84% identity with the cloned human Y2 receptor. These data indicate a wide distribution of Y receptors in small intestine and colon. They also suggest that Y1, Y2, Y4, and Y5 receptors may be responsible for still unexplained effects of PYY, NPY, or PP on secretion in small and large intestines.

Gut hormone concentrations in preterm infants with necrotizing enterocolitis

Blood levels of gastrin, neurotensin and vasoactive peptide (VIP) were estimated in 14 premature infants with necrotizing enterocolitis (NEC) and in 12 controls. In comparison to the control group, infants with NEC had (a) significantly lower gastrin levels both before [9.3 (7.8) versus 33.7 (27.1)] and after [52.4 (48.1) versus 100.8 (50.9)] the development of NEC; (b) significantly lower neurotensin levels only after the development of NEC [37.8 (10.4) versus 54.5 (20.6)1; and (c) no significant difference in VIP values [25.4 (9.7) versus 18.9 (9.9) and 24.5 (15.7) versus 26.1 (19.1)]. It is concluded that NEC can adversely affect gastrin and neurotensin concentrations in the blood.

Expression of receptors for gut peptides in human pancreatic adenocarcinoma and tumour-free pancreas

Gut hormones that modulate the growth of normal pancreas may also modulate the growth of cancers originating from pancreas. This study visualized and compared the receptors for cholecystokinin (CCK), bombesin (BBS), secretin and vasoactive intestinal peptide (VIP) in tumour-free tissue sections of human pancreas (n = 10) and pancreatic ductal adenocarcinomas (n = 12) with storage phosphor autoradiography using radioligands. CCK-B receptors, present in control pancreata, were not detected in any of the pancreatic cancers. BBS receptors were visualized in control pancreata, but they were absent in 10 of 12 pancreatic cancers. In 5 of 12 pancreatic cancers, receptors for secretin were visualized, while binding for secretin was present in all tumour-free pancreata. Conversely, no specific binding of VIP was detected in control pancreata but was identified in 3 of 12 pancreatic cancer specimens. It is concluded that the expression of gut peptide receptors in pancreatic cancer differs from that in tumour-free pancreas. Receptors for these peptides are present in only a minority of pancreatic cancer specimens.

Characterization of gene expression of VIP and VIP1-receptor in rat peritoneal lymphocytes and macrophages

In the present report we show the gene expression pattern of VIP and VIP1 receptor in two peritoneal cell populations, macrophages and lymphocytes by reverse transcription (RT) and polymerase chain reaction (PCR). Only in the lymphoid cells we have obtained a specific VIP cDNA product of 458 bp identical in size to the one obtained from cerebral cortex. On the other hand, we have obtained in both peritoneal populations lymphocytes and macrophages, a specific VIP1 receptor cDNA product of 311 bp identical in size to that obtained from lung. These results have been confirmed by Southern blot hybridization. Our findings suggest an autocrine/paracrine action of VIP in peritoneal microenvironment, supporting an immunoregulatory role for this neuropeptide.

G alpha i RNA antisense expression demonstrates the exclusive coupling of peptide YY receptors to G(i)2 proteins in renal proximal tubule cells

A clone PKSV-PCT Cl.10 referred to as Cl.10 was selected from the PKSV-PCT renal proximal tubule cell line which expressed peptide YY (PYY) receptors (Voisin, T., Bens, M., Cluzeaud, F., Vandewalle, A., and Laburthe, M. (1993) J. Biol. Chem. 268, 20547-20554). In order to identify G(i) protein(s) coupled to PYY receptors, antisense G alpha i protein RNAs were expressed in Cl.10 cells by transfecting the pcDNA3 vector into which were inserted 39 bases of the 5'-noncoding region of G alpha i2 or G alpha i3 used as specific antisense templates. A Cl.10/alpha i2-clone was selected which displayed a drastic decrease (> 90%) of the expression of G alpha i2 without changes of G alpha i3, G alpha s, and G beta subunits (G alpha i1 is not present in Cl.10 cells) as evidenced by Western blots. When compared to untransfected cells, this clone exhibited: (i) an increase in the dissociation constant of PYY receptors (5.3 versus 0.6 nM) identical to that observed in pertussis toxin-treated untransfected cells; (ii) an absence of inhibition of 125I-PYY binding by guanosine 5'-O-(thiotriphosphate) (GTP gamma S); and (iii) the failure of PYY to inhibit cAMP levels and to stimulate [methyl-3H]thymidine incorporation into DNA. A clone was also selected which exhibited a specific decrease (> 80%) of G alpha i3 as compared to untransfected cells. The sensitivity to GTP gamma S and the dissociation constant of PYY receptors as well as PYY-mediated inhibition of cAMP were identical to those observed in untransfected cells. These findings support an exclusive coupling of PYY receptors to G alpha i2.