RESUMEN
We examined whether the capsaicin vanilloid receptor-1 (VR1) mediates substance P (SP) release from primary sensory neurons in experimental pancreatitis. Pancreatitis was achieved by 12 hourly injections of caerulein (50 microg/kg ip) in mice. One group received capsazepine (100 micromol/kg sc), a competitive VR1 antagonist, at 4-h intervals. Neurokinin-1 receptor (NK1R) internalization in acinar cells, used as an index of endogenous SP release, was assessed by immunocytochemical quantification of NK1R endocytosis. The severity of pancreatitis was assessed by measurements of serum amylase, pancreatic myeloperoxidase (MPO) activity, and histological grading. Caerulein administration caused significant elevations in serum amylase and pancreatic MPO activity, produced histological evidence of pancreatitis, and caused a dramatic increase in NK1R endocytosis. Capsazepine treatment significantly reduced the level of NK1R endocytosis, and this was associated with similar reductions in pancreatic MPO activity and histological severity of pancreatitis. These results demonstrate that repeated caerulein stimulation causes experimental pancreatitis that is mediated in part by stimulation of VR1 on primary sensory neurons, resulting in endogenous SP release.
Asunto(s)
Capsaicina/análogos & derivados , Pancreatitis/metabolismo , Receptores de Droga/fisiología , Sustancia P/metabolismo , Amilasas/sangre , Animales , Capsaicina/farmacología , Endocitosis , Masculino , Ratones , Ratones Endogámicos C57BL , Páncreas/efectos de los fármacos , Páncreas/enzimología , Páncreas/patología , Páncreas/fisiopatología , Pancreatitis/patología , Pancreatitis/fisiopatología , Peroxidasa/metabolismo , Receptores de Neuroquinina-1/metabolismo , Índice de Severidad de la Enfermedad , Sustancia P/antagonistas & inhibidores , Canales Catiónicos TRPVRESUMEN
The mechanism by which Clostridium difficile toxin A causes substance P (SP) release and subsequent inflammation in the rat ileum is unknown. Pretreatment with the vanilloid receptor subtype 1 (VR1) antagonist, capsazepine, before toxin A administration significantly inhibited toxin A-induced SP release and intestinal inflammation. Intraluminal administration of the VR1 agonist capsaicin caused intestinal inflammation similar to the effects of toxin A. Pretreatment with capsazepine before capsaicin administration also significantly inhibited capsaicin-induced intestinal inflammation. These results suggest that intraluminal toxin A causes SP release from primary sensory neurons via stimulation of VR1 receptors resulting in intestinal inflammation.
Asunto(s)
Toxinas Bacterianas/farmacología , Capsaicina/análogos & derivados , Capsaicina/farmacología , Enteritis/tratamiento farmacológico , Enterotoxinas/farmacología , Íleon/efectos de los fármacos , Receptores de Droga/agonistas , Receptores de Droga/antagonistas & inhibidores , Sustancia P/metabolismo , Reacción de Fase Aguda/inducido químicamente , Animales , Toxinas Bacterianas/aislamiento & purificación , Capsaicina/uso terapéutico , Clostridioides difficile/patogenicidad , Relación Dosis-Respuesta a Droga , Interacciones Farmacológicas , Endocitosis/fisiología , Enteritis/inducido químicamente , Enteritis/patología , Enterotoxinas/aislamiento & purificación , Íleon/irrigación sanguínea , Íleon/enzimología , Íleon/microbiología , Íleon/cirugía , Inmunohistoquímica , Secreciones Intestinales/efectos de los fármacos , Secreciones Intestinales/metabolismo , Masculino , Inflamación Neurogénica/inducido químicamente , Neuronas/efectos de los fármacos , Neuronas/inmunología , Peroxidasa/metabolismo , Ratas , Sustancia P/antagonistas & inhibidores , Sustancia P/efectos de los fármacos , Factores de TiempoRESUMEN
Clostridium difficile enteritis is caused by toxin A (TA) which stimulates substance P release and subsequent receptor activation. This receptor stimulation results in secretion, inflammation, and structural damage. However, it is unclear as to which subset of neurons is required to initiate substance P release following toxin stimulation. Five centimeter ileal segments were surgically denervated. After 10 days, three ileal loops were constructed in each rat: the denervated loop was injected intraluminally with 5 microg of TA and two intact loops were injected with TA or vehicle, respectively. Ileal secretion, myeloperoxidase activity, and histology were then assessed. Denervated ileal loops injected with TA had a 75% reduction in ileal secretion (P < 0.001), 92% reduction in myeloperoxidase activity (P < 0.01) and 96% reduction in histologic damage (P < 0.001) compared to innervated loops. There were no significant differences between the denervated loops injected with TA and those injected with vehicle. Extrinsic surgical denervation results in protection of ileal loops from TA enteritis. Furthermore, these results exclude the participation of intrinsic enteric nerves in TA-induced ileal damage. Finally, this suggests that extrinsic primary sensory neurons mediate the effects of intraluminal TA in the ileum.
Asunto(s)
Desnervación Autonómica , Toxinas Bacterianas/farmacología , Clostridioides difficile , Enterocolitis Seudomembranosa/cirugía , Enterotoxinas/farmacología , Animales , Sistema Nervioso Entérico/microbiología , Sistema Nervioso Entérico/cirugía , Enterocolitis Seudomembranosa/inducido químicamente , Enterocolitis Seudomembranosa/prevención & control , Íleon/enzimología , Íleon/inervación , Íleon/microbiología , Peroxidasa/metabolismo , Ratas , Ratas Sprague-Dawley , Sustancia P/metabolismoRESUMEN
125I-monitor peptide binding was performed using frozen sections of the rat liver and gut and visualized using autoradiography. Saturable binding was observed in unidentified single cells in the liver and in the mucosa of the small intestine. Epidermal growth factor (EGF) and GTPgammaS did not inhibit 125I-monitor peptide binding indicating that the binding sites are not EGF receptors or G protein-coupled receptors. The liver binding site exhibited an affinity 3.7-4.4-fold higher than those in the small intestine. It has been established that intraluminal monitor peptide releases cholecystokinin from the small intestine. The present results indicate that monitor peptide may also have liver associated functions.
Asunto(s)
Sustancias de Crecimiento/metabolismo , Péptidos y Proteínas de Señalización Intercelular , Intestino Delgado/química , Hígado/química , Receptores de Péptidos/aislamiento & purificación , Animales , Autorradiografía , Unión Competitiva , Colecistoquinina/metabolismo , Clonación Molecular , Factor de Crecimiento Epidérmico/metabolismo , Hormonas Gastrointestinales/genética , Hormonas Gastrointestinales/metabolismo , Sustancias de Crecimiento/genética , Guanosina 5'-O-(3-Tiotrifosfato)/metabolismo , Radioisótopos de Yodo , Hormonas Pancreáticas/genética , Hormonas Pancreáticas/metabolismo , Unión Proteica , Ratas , Inhibidor de Tripsina Pancreática de Kazal/genética , Inhibidor de Tripsina Pancreática de Kazal/metabolismoRESUMEN
Multiple receptor subtypes specific for the neuropeptide Y (NPY)/peptide Y (PYY) family of peptides exist in mammals, but little is known about the distribution of this receptor family in other vertebrates. Saturable binding sites for 125I-labeled porcine PYY were localized in frozen sections of the brain of the smooth dogfish (Mustelis canis) by radioligand binding and autoradiography. Saturable 125I-porcine PYY binding sites were distributed widely in the cerebral hemispheres, optic lobes, hypothalamus, cerebellum and hindbrain. Binding was saturable, specific for PYY and related peptides, and of high affinity (Kd = 2.53 nM). The specificity of the binding site was analyzed by performing competitive inhibition experiments with nonradioactive PYY, NPY, and [Leu31, Pro34]-NPY and NPY13-36, synthetic peptide analogs specific for the mammalian Y1 and Y2 receptor subtypes, respectively. Saturable 125I-porcine PYY binding sites in all regions of the dogfish brain closely resembled the mammalian Y1 NPY receptor subtype in specificity for these substances. There was no evidence for expression of multiple receptor subtypes. We conclude that a single receptor specific for the NPY/PYY family of peptides is widely expressed in the smooth dogfish brain and that this receptor closely resembles the mammalian Y1 receptor subtype, suggesting that the Y1 receptor is the ancestral receptor in this family.
Asunto(s)
Química Encefálica , Neuropéptido Y/metabolismo , Péptidos/metabolismo , Receptores de la Hormona Gastrointestinal/análisis , Receptores de Neuropéptido Y/análisis , Animales , Autorradiografía , Sitios de Unión/fisiología , Unión Competitiva , Evolución Biológica , Cazón , Péptido YY , Ensayo de Unión RadioliganteRESUMEN
Bombesin stimulates cholecystokinin (CCK) secretion, presumably by a direct effect on the intestinal CCK cell. The present objectives were to characterize bombesin-stimulated CCK release and to investigate the role of calcium in CCK secretion in an intestinal CCK-producing cell line (STC-1). Bombesin caused a dose-dependent release of CCK, which was reduced either in the absence of extracellular calcium or by calcium channel blockade, suggesting that influx of calcium is necessary for CCK secretion. Bombesin caused an increase in intracellular calcium concentration ([Ca2+]i) and increased efflux of 45Ca2+ from 45Ca(2+)-loaded cells. Radioligand binding studies and Northern analysis were consistent with the expression of a bombesin receptor. Thus bombesin stimulation of CCK release occurs via binding to a receptor and is dependent on increased [Ca2+]i. We propose that the STC-1 cell line may provide a useful model for studying the regulation of intestinal CCK secretion.
Asunto(s)
Bombesina/farmacología , Colecistoquinina/metabolismo , Mucosa Intestinal/metabolismo , Animales , Calcio/metabolismo , Línea Celular , Ratones , Receptores de Bombesina/metabolismo , Células Tumorales CultivadasRESUMEN
Antibodies to neuropeptide receptors can be used to localize and characterize the receptors in tissues and cell lines. Two strategies were used to study the rat substance P receptor (SPR, NK-1) by immunological methods. First, a polyclonal antiserum was raised by immunizing rabbits with a peptide corresponding to the 15 amino acid residues (KTMTESSSFYSNMLA, SPR393-407) at the intracellular C-terminus of the rat SPR coupled to bovine thyroglobulin. An antiserum was obtained with a titer for half-maximal binding of 125I-SPR393-407 of 1:70,000. Nonradioactive SPR393-407 inhibited 50% of binding at a concentration of 10 pM. Binding of 125I-SPR393-407 to the antiserum was also displaced in a parallel manner by membrane proteins from tissues expressing high levels of the SPR (brain and submaxillary gland). Second, a chimeric SPR construct of a hydrophilic Flag peptide (DYKDDDDK) genetically engineered in sequence with the extracellular N-terminus of rat SPR was generated by polymerase chain reaction. The Flag-SPR chimera was expressed in rat kidney epithelial cells (KNRK) and judged to be fully functional, assessed by binding of 125I-substance P (apparent Kd of 5.63 nM) and calcium mobilization in response to substance P (EC50 of 0.66 nM). Antibodies to SPR393-407 and the Flag peptide stained the plasma membrane of KNRK cells expressing the native SPR or the Flag-SPR chimera. Staining was abolished by preincubation with SPR393-407 or the Flag peptide. Cells transfected with vector alone were unstained. The SPR antiserum recognized a broad protein band on Western blots of membranes prepared from cells expressing SPR but not from cells transfected with vector alone. The signal was quenched by preincubation of the antiserum with SPR393-407. By immunohistochemistry, the SPR antiserum was found to bind to neurons in the dorsal horn of the rat spinal cord and to ganglion cells in the myenteric plexus of the rat ileum near substance P-immunoreactive nerve fibers. Staining was abolished by preabsorption of the antiserum with SPR393-407. These antibodies can be used to localize the SPR in tissues and cells and to examine the function of the receptor in cell lines.
Asunto(s)
Anticuerpos , Neuronas/metabolismo , Receptores de Neuroquinina-1/análisis , Receptores de Neuroquinina-1/biosíntesis , Médula Espinal/metabolismo , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Western Blotting , Línea Celular , Clonación Molecular , Cartilla de ADN , Inmunohistoquímica , Radioisótopos de Yodo , Cinética , Masculino , Datos de Secuencia Molecular , Neuronas/citología , Péptidos/inmunología , Conejos/inmunología , Radioinmunoensayo , Ratas , Ratas Endogámicas F344 , Receptores de Neuroquinina-1/inmunología , Proteínas Recombinantes de Fusión/análisis , Proteínas Recombinantes de Fusión/biosíntesis , Proteínas Recombinantes de Fusión/inmunología , Médula Espinal/citología , Sustancia P/metabolismo , TransfecciónRESUMEN
A [125I]cholecystokinin (CCK) analog and [125I]peptide YY (PYY) were used to localize and characterize CCK and neuropeptide Y (NPY) receptor binding sites in the rabbit vagal afferent (nodose) ganglion. High concentrations of CCK and NPY binding sites were observed in 10.6% and 9.2% of the nodose ganglion neurons, respectively. Pharmacological experiments using CCK or NPY analogs suggest that both subtypes of CCK (CCK-A and CCK-B) and NPY (Y1 and Y2) receptor binding sites are expressed by discrete populations of neurons in the nodose ganglion. These results suggest sites at which CCK or NPY, released in either the nucleus of the solitary tract or a peripheral tissue, may modulate the release of neurotransmitters from a select population of visceral primary afferent neurons. Possible functions mediated by these receptors include modulation of satiety, opiate analgesia, and the development of morphine tolerance.
Asunto(s)
Neuronas Aferentes/fisiología , Ganglio Nudoso/fisiología , Receptores de Colecistoquinina/fisiología , Receptores de Neuropéptido Y/fisiología , Secuencia de Aminoácidos , Animales , Colecistoquinina/análogos & derivados , Colecistoquinina/metabolismo , Radioisótopos de Yodo , Masculino , Datos de Secuencia Molecular , Neuronas Aferentes/efectos de los fármacos , Neuronas Aferentes/metabolismo , Neuropéptido Y/análogos & derivados , Neuropéptido Y/metabolismo , Ganglio Nudoso/citología , Ganglio Nudoso/metabolismo , Conejos , Receptores de Colecistoquinina/biosíntesis , Receptores de Colecistoquinina/efectos de los fármacos , Receptores de Neuropéptido Y/biosíntesis , Receptores de Neuropéptido Y/efectos de los fármacosRESUMEN
Frozen sections of the rat stomach were incubated with 125I-labeled porcine secretin, and then secretin binding sites were localized by autoradiography. Saturable binding was observed only in the muscularis externa (circular and longitudinal smooth muscle layers) of the proximal nonglandular forestomach. Saturable binding was quantitated by densitometry. 125I-porcine secretin bound to a single class of high-affinity binding sites with a dissociation constant of 0.6 nM. Porcine and rat secretins were nearly equipotent in inhibiting saturable 125I-porcine secretin binding, and vasoactive intestinal polypeptide, peptide histidine-isoleucine, and glucagon were much weaker. Carbachol (100 microM) stimulated a sustained increase in tension in forestomach muscle in vitro, and porcine secretin caused relaxation of this stimulated contraction. We conclude that rat forestomach smooth muscle expresses a high-affinity specific secretin binding site that mediates relaxation. This putative secretin receptor may mediate some of the actions of secretin on gastric motility.
Asunto(s)
Relajación Muscular/efectos de los fármacos , Músculo Liso/fisiología , Receptores de la Hormona Gastrointestinal/fisiología , Secretina/metabolismo , Secretina/farmacología , Estómago/fisiología , Animales , Autorradiografía , Unión Competitiva , Carbacol/farmacología , Mucosa Gástrica/metabolismo , Técnicas In Vitro , Radioisótopos de Yodo , Cinética , Contracción Muscular/efectos de los fármacos , Músculo Liso/metabolismo , Ratas , Receptores Acoplados a Proteínas G , Receptores de la Hormona Gastrointestinal/metabolismo , PorcinosRESUMEN
[125I]Peptide YY was used to localize and characterize peptide YY and neuropeptide Y receptor binding sites in the heart. In the rat and rabbit heart, nearly every artery and arteriole that could be histologically identified also expressed saturable binding sites for [125I]peptide YY. In the arteries, these [125I]peptide YY binding sites were primarily associated with the smooth muscle layer. Pharmacological experiments demonstrated that peptide YY and neuropeptide Y were equipotent in competing for [125I]peptide YY binding in the heart. In another competition series, [Leu31,Pro34]-neuropeptide Y (a Y1 receptor-specific agonist when used with [125I]peptide YY) was significantly more potent than neuropeptide Y (a Y2 receptor-specific agonist when used with [125I]peptide YY) in competing for [125I]peptide YY binding from coronary arteries, suggesting that the receptor binding sites on cardiac arteries and arterioles are of the Y1 subtype. These results demonstrate that smooth muscle cells of the atrial and ventricular arteries and arterioles in rat and rabbit heart express Y1 receptors and suggest a possible direct effect of neuropeptide Y on coronary blood vessels to induce vasoconstriction.
Asunto(s)
Hormonas Gastrointestinales/metabolismo , Miocardio/metabolismo , Péptidos/metabolismo , Receptores de Neuropéptido Y/metabolismo , Animales , Autorradiografía , Vasos Coronarios/efectos de los fármacos , Vasos Coronarios/metabolismo , Corazón/efectos de los fármacos , Procesamiento de Imagen Asistido por Computador , Radioisótopos de Yodo , Masculino , Péptido YY , Conejos , Ensayo de Unión Radioligante , Ratas , Ratas Sprague-Dawley , Receptores de Neuropéptido Y/efectos de los fármacos , Coloración y EtiquetadoRESUMEN
Bombesin binding sites were localized in the rat urogenital system by autoradiography of 125I-Tyr4-bombesin binding to frozen tissue sections. Saturable binding was observed in the bladder, seminal vesicle, uterus, and oviduct. In all organs, the binding sites corresponded to layers of smooth muscle. Radioligand binding studies were performed on homogenized membrane preparations from bladder, uterus, and seminal vesicle. Membrane binding was saturable, reversible, time- and temperature-dependent, and specific for bombesin and related peptides. Analysis of saturable equilibrium binding from all three organs yielded a best fit to a one-site model of high affinity binding with apparent KdS of 720 pM for bladder, 470 pM for uterus, and 700 pM for seminal vesicle. Neuromedin B was potent in displacing saturable 125I-Tyr4-bombesin binding from bladder and seminal vesicle but not uterus membranes. In order to characterize these binding sites further, the ability of these membranes to interact with a specific bombesin receptor antagonist, [Leu13-psi-CH2NH-Leu14]-bombesin, and with GTP-gamma-S was determined. [Leu13-psi-CH2NH-Leu14]-bombesin was much more potent in displacing saturable 125I-Tyr4-bombesin binding from uterus than from bladder and seminal vesicle membranes, further supporting the distinction between the uterus and the bladder/seminal vesicle binding sites as bombesin receptor subtypes. GTP-gamma-S inhibited saturable 125I-Tyr4-bombesin binding to membranes from all three organs, indicating that both receptor subtypes are linked to GTP-binding proteins. We conclude that smooth muscle in the rat urogenital system expresses bombesin receptors and that endogenous GRP and neuromedin B may regulate some reproductive and excretory functions. The bladder and seminal vesicle express the neuromedin B-preferring subtype and the uterus expresses the bombesin/GRP-preferring subtype of bombesin receptor.
Asunto(s)
Receptores de Neurotransmisores/metabolismo , Sistema Urogenital/metabolismo , Secuencia de Aminoácidos , Animales , Autorradiografía , Femenino , Guanosina 5'-O-(3-Tiotrifosfato)/metabolismo , Técnicas In Vitro , Radioisótopos de Yodo , Masculino , Datos de Secuencia Molecular , Ensayo de Unión Radioligante , Ratas , Receptores de Bombesina , Vejiga Urinaria/efectos de los fármacosRESUMEN
Secretin is thought to cause choleresis by acting on a receptor expressed by bile duct epithelial cells. In this study, the receptor was characterized using a new preparation of intrahepatic bile duct plasma membranes. Hyperplastic biliary trees were obtained from 3-week bile duct-ligated rats. The biliary trees were homogenized, filtered, and subjected to an aqueous two-phase partition technique to yield highly purified plasma membranes (confirmed by a 14-fold enrichment in gamma-glutamyl transpeptidase activity and a 10-fold enrichment in 125I-secretin binding). 125I-secretin bound saturably with high affinity and in a dose-dependent fashion (Kd = 1.3 +/- 0.1 nM, Bmax = 273 +/- 23 fmole/mg) to purified plasma membranes. The binding characteristics of secretin were most consistent with a single site receptor model. Competitive binding studies indicated that the secretin-related peptides glucagon, peptide histidine isoleucine, gastric inhibitory peptide, and growth hormone releasing factor did not inhibit binding. Vasoactive intestinal peptide (1 microM) reduced maximal binding by 19 +/- 1%. The GTP analogs guanylylimidodiphosphate and guanosine 5'-O-[3-thiotriphosphate] (1 microM) inhibited binding by 16 +/- 2 and 13 +/- 1%, respectively. In conclusion, secretin binds to a specific, high-affinity receptor in intrahepatic bile duct epithelium that is coupled to a G-protein-linked signal transduction system.
Asunto(s)
Conductos Biliares Intrahepáticos/metabolismo , Membrana Celular/metabolismo , Receptores de la Hormona Gastrointestinal/metabolismo , Animales , Unión Competitiva , Fraccionamiento Celular , Epitelio/metabolismo , Guanosina 5'-O-(3-Tiotrifosfato)/farmacología , Guanilil Imidodifosfato/farmacología , Cinética , Masculino , Ratas , Ratas Sprague-Dawley , Receptores Acoplados a Proteínas G , Secretina/metabolismo , Péptido Intestinal Vasoactivo/metabolismo , gamma-Glutamiltransferasa/metabolismoRESUMEN
125I-Bolton-Hunter sulfated cholecystokinin-8 was used to localize and characterize cholecystokinin (CCK) receptor binding sites in trigeminal and dorsal root ganglia, and in the spinal cord of the rat, rabbit, and monkey. In the rabbit and monkey, a substantial number, 90 +/- 21% and 24 +/- 8%, respectively, of trigeminal and dorsal root ganglion neurons express CCK binding sites. In the spinal cord, the highest concentration of CCK receptors is found in laminae I and II, which is the major termination site of dorsal root ganglia neurons expressing CCK receptor binding sites. Neonatal capsaicin treatment of the rat results in a 70% decline in CCK receptor binding sites in laminae I and II of the spinal cord, indicating that dorsal root ganglia neurons are a major source of CCK receptors in the spinal cord. Pharmacological experiments using selective CCK-A and CCK-B receptor antagonists demonstrate that CCK-B is the prominent CCK receptor subtype in trigeminal and dorsal root ganglia neurons in the rat, rabbit, and monkey. In the rat and rabbit spinal cord, CCK-B binding sites are the prominent subtype, whereas in the monkey cord, CCK-A is the prominent receptor subtype. These results demonstrate that CCK-B receptors are expressed by a substantial percentage of dorsal root ganglion neurons at all spinal levels, and that CCK may antagonize opiate analgesia at the level of the primary afferent neuron itself.
Asunto(s)
Ganglios Espinales/metabolismo , Neuronas/metabolismo , Receptores de Colecistoquinina/metabolismo , Médula Espinal/metabolismo , Ganglio del Trigémino/metabolismo , Analgésicos/metabolismo , Animales , Autorradiografía , Ganglios Espinales/fisiología , Radioisótopos de Yodo , Macaca nemestrina , Masculino , Narcóticos/metabolismo , Neuronas/fisiología , Conejos , Ratas , Ratas Sprague-Dawley , Receptores de Colecistoquinina/fisiología , Receptores de Neurotransmisores/metabolismo , Sincalida/análogos & derivados , Sincalida/metabolismo , Especificidad de la Especie , Succinimidas/metabolismo , Ganglio del Trigémino/fisiologíaRESUMEN
Pancreatic polypeptide (PP) is released from pancreatic islets after meals or in response to stress. Although PP exhibits a wide spectrum of biological effects, few, if any, are mediated by a direct action of PP on its ultimate target organ. Recently, PP receptors have been identified in areas of the brain with an incomplete blood-brain barrier suggesting that PP may act indirectly through the central nervous system. In the present study, we sought to identify peripheral PP binding sites using an in vivo radioreceptor assay and in vitro autoradiography. Using these techniques, we have identified saturable binding sites for PP in the zona fasciculata, zona reticularis, and the medulla of the rat adrenal gland. We have characterized these sites using equilibrium analysis of membrane-radioligand binding and by quantitative autoradiography of radioligand binding to frozen tissue sections. Binding of PP to these sites is saturable, of high affinity, and specific as well as time, temperature, and membrane dependent. Moreover, PP binds to these putative receptor sites in vivo at physiological concentrations. Many of the actions of PPs have been demonstrated to be indirect. Because PP receptors have been identified in the brain and now in the adrenal gland, we suggest that some of the effects of PP may be mediated through direct and indirect modulation of the brain and adrenal axis.
Asunto(s)
Glándulas Suprarrenales/química , Polipéptido Pancreático/metabolismo , Receptores de la Hormona Gastrointestinal/análisis , Glándulas Suprarrenales/citología , Animales , Autorradiografía , Unión Competitiva , Radioisótopos de Yodo , Cinética , Hígado/metabolismo , Masculino , Ensayo de Unión Radioligante , Ratas , Ratas Endogámicas , TermodinámicaRESUMEN
The goal of the present studies was to identify and characterize the site of secretin action in the liver. Sections of normal and bile duct-ligated rat livers were used for in vitro 125I-secretin receptor autoradiography. Saturable binding was observed in both normal and bile duct-ligated livers but was much greater in the bile duct-ligated preparations. Binding was limited to biliary epithelium and the increased secretin binding observed in the ligated livers correlated with the increase in ductular tissue. Saturable binding was inhibited in a dose-dependent fashion by increasing concentrations of nonradioactive secretin. Analysis of saturation binding showed that 125I-secretin binding was best fit by a one-site receptor model with a Kd of 5.3 +/- 1.1 nmol/L. Glucagon, vasoactive intestinal polypeptide, gastric inhibitory polypeptide, growth hormone-releasing hormone, and cholecystokinin did not inhibit saturable 125I-secretin binding at concentrations of 1 pmol/L to 1 mumol/L. The authors conclude that high-affinity, specific secretin binding sites are present in rat intrahepatic biliary epithelium. When bile ducts are stimulated to proliferate by bile duct ligation, secretin binding is also increased.