Compared Binding Properties of 125I-Labeled Analogues of Neurotensin and Neuromedin N in Rat and Mouse Brain

Abstract: Neurotensin and neuromedin N are two structurally related peptides that are synthesized by a common precursor. The purpose of the present work was to characterize neuromedin N receptors in rat and mouse brain and to compare these receptors with those of neurotensin. A radiolabeled analogue of neuromedin N has been prepared by acylation of the N-terminal amino group of the peptide with the ¹²⁵I-labeled Bolton-Hunter reagent. This ¹²⁵I-labeled derivative of neuromedin N bound to newborn mouse brain homogenate with high affinity (K _d = 0.5 n M ). Cross-competition experiments between radiolabeled and unlabeled neurotensin and neuromedin N indicated that each peptide was able to displace completely and specifically the other peptide from its interaction with its receptor. Independently of the radioligand used, the affinity of neurotensin was always better than that of neuromedin N. Quantitative radioautographic studies demonstrated that the ratio of labeling intensities obtained with ¹²⁵I-labeled analogues of neurotensin and neuromedin N remained constant in all the brain areas. Our results do not support the existence of a specific neuromedin N receptor in rat and mouse brain and can be explained by the presence of a common receptor for both peptides.     

Neuromedin N: presence and chromatographic characterization in the rat

The distribution of neuromedin N and its structurally related peptide, neurotensin, was investigated in the rat and found to be remarkably similar with highest concentrations in the ileum. However, neuromedin N but not neurotensin was found in the kidney. Chromatographic analysis of immunoreactive neuromedin N demonstrated a single peak of immunoreactivity which was distinguishable from the single peak of immunoreactive neurotensin. Neuromedin N is likely to be a naturally occurring peptide and is distinct from neurotensin in rat peripheral tissues.     

Neurotensin Binding to Human Embryonic Lung Fibroblasts

Abstract

Several neuropeptides have been shown to regulate the function of cells involved in immune response and inflammation. Neurotensin is a 13 amino acid neuropeptide localized primarily to the nervous system and gut. Neurotensin also stimulates mast cell degranulation and enhances phagocytic and cytolytic capability of macrophages, suggesting that this peptide regulates inflammatory and immune responses. Fibroblasts play an important role in inflammation and tissue healing, and these processes may be regulated by several neuropeptides that have been shown to bind to fibroblasts. However neurotensin receptors have not been identified on fibroblasts. Human embryonic lung fibroblasts (HELF) were examined for binding and biological effects of neurotensin. ¹²⁵I-neurotensin binding to adherent and confluent human embryonic lung fibroblasts (HELF), plated in 12mm diameter wells was specific and saturable. Computer-assisted resolution of the binding data demonstrated two classes of binding sites: a high affinity, low capacity site (K_d = 1.6×10^?11 M, 19.5×10⁷ sites/well), and a low- affinity, high-capacity site (K_d = 10^?8 M, 4×10⁹ sites/well). Neurotensin stimulated immediate, transient, dose-dependent increases of cytosolic calcium in HELF (threshold dose: 10¹¹ M), suggesting release of calcium from intracellular stores. The novel finding of neurotensin receptors on fibroblasts provides further support for this neuropeptide's role as a regulator of inflammatory and immune responses.     

Potentiation by thiorphan and bestatin of the naloxone-insensitive analgesic effects of neurotensin and neuromedin n

Neurotensin induced significant antinociceptive activity as measured in a variety of nociceptive tests 10 and 30 min following intracerebroventricular (i.c.v.) injection in mice. The lowest effective peptide doses were 25 ng in the writhing test, 25–50 ng in the tail-flick test, 50–100 ng in the hot-plate test and 2000 ng in the tail electrical stimulation test. The neurotensin related hexapeptide neuromedin N also displayed antinociceptive properties but only in the writhing and tail-flick tests. Furthermore, as compared to neurotensin, the neuromedin effects required higher doses. ED₅₀'s for neurotensin and neuromedin in the writhing test were 70 ng and 1070 ng, respectively. Separate or combined injections of the endopeptidase 24.11 (enkephalinase) inhibitor thiorphan (l0μg) and the aminopeptidase inhibitor bestatin (50μg) did not affect tail-flick latencies. In contrast, i.c.v. injection of thiorphan together with an ineffective dose of neurotensin (25 ng) resulted in a significant antinociceptive effect. Bestatin did not modify tail-flick latencies in neurotensin-treated mice whether in the absence or presence of thiorphan. On the contrary, each of these peptidase inhibitors promoted antinociceptive effects of subthreshold doses of neuromedin (lμg) in the tail-flick test. Maximal antinociception was obtained by combining both inhibitors, thus conferring antinociceptive effects to neuromedin doses that were as low as 10 ng. Naloxone (0.5–2 mg/kg, s.c.) did not significantly reduced the antinociceptive effects of combinations of neurotensin and thiorphan and of neuromedin, thiorphan and bestatin. The data show that both neurotensin and neuromedin elicit analgesia in mice through an opiate independent mechanism. Furthermore, like enkephalin, neuromedin is readily degraded by brain endopeptidase 24.11 and bestatin sensitive aminopeptidase(s), whereas the resistance of neurotensin to aminopeptidase attack confers to this peptide a broader spectrum and longer duration of action than its congener neuromedin.     

Isolation and quantitation of several new peptides from the canine neurotensin/neuromedin N precursor

Using antisera towards the bioactive peptides, neurotensin and neuromedin N, as well as towards the N-terminal and C-terminal regions of their shared 170-residue precursor, peptides representing various portions of the precursor were isolated from extracts of canine ileum. In total, seven peptides were isolated, two of which had not been previously identified. One was the C-terminal tail of the precursor (Gly-Ser-Tyr-Tyr-Tyr) and the other was the tail peptide extended N-terminally to include neurotensin (Glp-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu-Lys-Arg-Gly-Ser-Tyr-Tyr-Tyr). By comparing the measured concentrations for each of the identified peptides, it was established that processing at the three Lys-Arg cleavage sites within the precursor did not occur to the same extent. Cleavage at the N-terminus of neuromedin N was 10% complete, that between neurotensin and the tail was 90% complete, and that between neuromedin N and neurotensin was 95% complete. Three immunoreactive proteins were also identified by immunochemical and chromatographic analyses: N-terminally extended neuromedin N (125 residues), N-terminally extended neurotensin (140 residues), and the entire 147-residue precursor. It was concluded that neurotensin, tail and large molecular neuromedin N were the primary products of processing for this precursor in canine ileum, while minor products included neuromedin N, neurotensin tail, and large molecular neurotensin.     

Calcium modulation and chemotactic response: divergent stimulation of neutrophil chemotaxis and cytosolic calcium response by the chemotactic peptide receptor

Stimulation of neutrophils by chemoattractants is followed by a rapid, transient rise in cytosolic calcium concentration. The role of calcium in activation of cell movement and related responses was examined by selectively chelating extracellular or both extra- and intracellular calcium. Removal of calcium from the extracellular medium did not alter the cytosolic calcium concentration (Quin 2 fluorescence, 110 to 120 nM) of unstimulated neutrophils and did not dramatically affect the rise induced by formyl peptide. Despite the intact Quin 2 response, depletion of extracellular calcium partially inhibited chemotaxis, adherence to substrate, and polarization (increased forward light scatter) in response to formyl peptide. Loading neutrophils with Quin 2 in the absence of calcium depressed cytosolic Ca2+ to 10 to 20 nM and abrogated a detectable rise with formyl peptide stimulation. Depletion of intracellular calcium further inhibited chemotaxis and polarization, although neutrophils still demonstrated significant directed migration and shape change to formyl peptide (30 to 40% of control) without an increase in Quin 2 fluorescence. Other neutrophil responses related to chemotaxis (decreased right-angle light scatter, actin polymerization) were minimally affected by depletion of calcium from either site. The data indicate that neutrophil chemotaxis and related responses to formyl peptide may be activated by intracellular signals not detectable with Quin 2.     

Neurotensin and Neuromedin N Are Differently Metabolized in Ventral Tegmental Area and Nucleus Accumbens

Whole homogenates and membrane-bound and cytosoluble fractions prepared from rat ventral tegmental area (VTA) and nucleus accumbens were examined for their content of peptidasic activities and for their ability to metabolize neurotensin and its natural related hexapeptide neuromedin N. No qualitative differences were observed between these two brain regions concerning the presence and the subcellular distribution of a series of activities able to hydrolyze various specific fluorimetric enzymatic substrates. However, aminopeptidase B, endopeptidase 24-15, and endopeptidase 24-11 were significantly lower in the VTA than in the nucleus accumbens membrane preparations, while proline endopeptidase was detected in significantly higher amount only in the cytosolic fraction prepared from nucleus accumbens. Both neurotensin and neuromedin N were metabolized more rapidly in the nucleus accumbens than in the VTA. Furthermore, the degradation rate of neuromedin N was considerably faster than that of neurotensin whatever the cerebral area examined. Studies carried out with highly specific peptidase inhibitors revealed that endopeptidase 24-15 mainly contributed to the catabolism of neurotensin in homogenates and membrane-bound preparations of nucleus accumbens and VTA, while aminopeptidase B appeared predominantly responsible for the rapid disappearance of neuromedin N in both cerebral tissues. The possibility that the different metabolic processes of the two peptide congeners could explain their distinct pharmacological profiles observed after their microinjection in the nucleus accumbens and in the VTA is discussed.     

Inhibitory and excitatory mechanisms of neurotensin action in canine intestinal circular muscle in vitro.

The effect of neurotensin on canine ileal circular muscle devoid of myenteric plexus was investigated using single and double sucrose gap techniques. Similar results were obtained with microelectrode techniques. Neurotensin caused a temperature-sensitive and dose-dependent biphasic response, an initial hyperpolarization associated with inhibition of contractile activity, followed by an excitatory phase, usually consisting of spike discharge and tonic and phasic contractions, for which depolarization was not required. Neither response was affected by tetrodotoxin, phentolamine, propranolol, or atropine. The hyperpolarization was associated with decreased membrane resistance, blocked by 10(-7) M apamin, and converted to tonic depolarization by apamin (10(-6) M). Tachyphylaxis to neurotensin occurred when the stimulation interval was less than 20 min. After Ca2+ depletion, depolarization was observed instead of the hyperpolarization; this depolarization was not affected by nitrendipine and was gradually abolished with repetitive stimulation at 20-min intervals. When Ca2+ was present, nifedipine did not alter the hyperpolarizing phase of the response but inhibited spiking and blocked all contractions. The excitatory phase of the response was enhanced by Bay K-8644. Neuromedin N elicited a response identical with that of neurotensin. The responses of the two peptides were completely cross tachyphylactic. Inhibitory junction potentials were not affected by neurotensin tachyphylaxis. It is concluded that neurotensin and neuromedin N activate apamin-sensitive, calcium-dependent potassium channels in circular muscle, causing membrane hyperpolarization and inhibition of muscle contraction. Release of intracellular calcium is involved in the activation of these potassium channels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of cholecystokinin and gastrin on human peripheral blood lymphocyte functions, implication of cyclic AMP and interleukin 2

The effects in vitro of sulphated and desulphated cholecystokinin (CCK)-8, and of gastrin-17 and gastrin-34 were studied at concentrations from 10⁻¹⁴ M to 10⁻⁶ M on several functions of human peripheral blood lymphocytes, i.e.: adherence to substrate, mobility (spontaneous and directed by a chemical gradient or chemotaxis), and spontaneous and phytohaemagglutinin (PHA)-mediated proliferation. All peptides, at concentrations from 10⁻¹⁰ M to 10⁻⁸ M, inhibited significantly the mobility capacity and PHA-induced proliferation, and increased the adherence and spontaneous proliferation. A dose-response relationship was observed, with a maximum response of lymphocyte functions at 10⁻¹⁰ M. These peptides induced a significant increase of intracellular cAMP levels at 30 and 60 sec. Because lymphoproliferation requires production of interleukin 2 (IL-2) by lymphocytes, we also measured the IL-2 production in the presence of the CCK and gastrin peptides, finding that this production was higher than in the respective controls. When peptides were added to samples containing PHA, the IL-2 production was significantly decreased with respect to samples incubated with PHA alone. These results suggest that the CCK and gastrin peptides are negative modulators of lymphocyte mobility (spontaneous mobility and chemotaxis), causing an inhibition of these activities through an increase of intracellular cAMP levels, and of PHA-induced lymphoproliferation, which is mediated by a diminution of the IL-2 production by lymphocytes.     

Nitric oxide released by accessory cells mediates the gastrin-releasing peptide effect on murine lymphocyte chemotaxis

Several neuropeptides, including gastrin-releasing peptide (GRP), modulate the immune response, specifically lymphocyte chemotaxis. In the present work the effect of GRP on the chemotaxis of murine lymphocytes from different immune locations in both, total leukocyte populations and populations depleted of adherent cells have been studied. Specificity of the GRP effect on chemotaxis using an antagonist of the GRP receptor, as well as the implication of nitric oxide (NO), using inhibitors of NO synthase and donors of NO, were investigated. The effects of GRP stimulating the chemotaxis of lymphocytes from peritoneum, axillary nodes and spleen and decreasing the chemotaxis from thymus were receptor-specific and disappeared in lymphocytes from populations depleted of adherent cells. NO synthase inhibitors blocked the GRP effect on lymphocyte chemotaxis, and this action was reversed in the presence of l-arginine. Thus, the effect of GRP on murine lymphocyte chemotaxis appears to be mediated by NO secreted by adherent cells.     

Release of ileal neurotensin in the rat by neurotransmitters and neuropeptides.

To investigate the functional relationship between the enteric nervous system and the intestinal neurotensin (N) cells, the release of neurotensin (NT) was measured upon vascular 8-min infusion periods of various neurotransmitters and neuropeptides in an isolated vascularly perfused rat jejunoileum. NT-like immunoreactivity (NT-LI) was measured with an antiserum that specifically recognizes intact NT. The cholinergic agonists methacholine and carbachol produced a strong release of NT-LI (250% and 700% of basal, respectively at 10(-5) M). The infusion of a lower dose (10(-7) M) was less effective in both cases. The nicotinic receptor agonist DMPP (10(-4) M) had no significant effect on NT-LI release. Norepinephrine (10(-6) M) produced a moderate and well-sustained secretion of NT (200% of basal). Infusion of higher doses of these neurotransmitters dramatically increased the arterial pressure. G-amino-n-butyric acid (GABA), histamine, serotonin and dopamine administered at final concentrations up to 10(-5) M had no effect on NT-LI release. In contrast, gastrin-releasing peptide and bombesin induced a dose-dependent transient increase of portal NT-LI (maximal value at 10(-7) M: 1000% of basal) followed by a rapid return to near basal values. Substance P (10(-7) M) evoked a prompt release of NT-LI with a peak at 600% of basal followed by a decline to 200% of basal at the end of the session. Leu-enkephalin and calcitonin-gene-related-peptide (CGRP, 10(-7) M) produced a small rise in portal NT-LI, while Met-enkephalin, dynorphin, vasoactive intestinal peptide (VIP), galanin, neuropeptide Y (NPY), peptide histidine isoleucine (PHI), neuromedin U and thyrotropin releasing hormone (TRH) had no stimulatory effect. Our results indicate that additionally to the secretion of NT induced by cholinergic agents and bombesin, substance P and to a lesser extent Leu-enkephalin are capable of stimulating NT release in the rat.     

Neuromedin N: a novel neurotensin-like peptide identified in porcine spinal cord

A novel neurotensin-like peptide, designated neuromedin N, has been isolated from porcine spinal cord by using a bioassay for a stimulant effect on guinea pig ileum. By microsequencing, the amino acid sequence of the peptide has been determined to be Lys-Ile-Pro-Tyr-Ile-Leu, which is found to be quite homologous to the COOH-terminal sequence of neurotensin. This structure has been confirmed by synthesis. Neuromedin N exhibits a contractile activity on guinea pig ileum and induces a hypotensive response in the rat similar to that with neurotensin. These findings suggest that neuromedin N may be a new neuromediator or hormone with a specific spectrum of biological activity.     

Specificity of action on neuropeptides of an endopeptidase from the synaptosomal membranes of guinea pig brain

An endopeptidase was solubilized and highly purified from the synaptosomal membrane fraction of guinea pig brain, and its specificity of action on various neuropeptides was investigated. It hydrolyzed specifically the Pro10-Tyr11 bond of neurotensin and showed a marked specificity toward Pro-X bonds present in the interior parts of various neuropeptides and related peptides. No cleavage, however, was observed at the first and second peptide bonds from the NH2-termini or from the COOH-termini of the peptides examined, suggesting that the enzyme requires both NH2- and COOH-terminal extentions of at least 3 residues from the scissile bond for its action. In addition, a limited number of other peptide bonds were cleaved, indicating that the enzyme is not strictly specific to Pro-X bonds. These results suggest the possible implication of this enzyme in the specific degradation of neurotensin and other peptide neurotransmitters in the synaptic cleft.     

Regulation of cyclic GMP levels by neurotensin in neuroblastoma clone N1E115

The binding of 125I-labeled [monoiodo-Tyr3]neurotensin to intact neuroblastoma N1E115 cells and the effect of neurotensin on the intracellular concentration of cyclic nucleotides were studied at 37 degrees C and under physiological conditions of pH and ionic strength. The radiolabeled neurotensin analogue bound specifically to differentiated cells with a dissociation constant of 0.75 nM and a maximal binding capacity of 45 fmol/10(6) cells. Incubation of neuroblastoma cells with neurotensin in the presence of calcium ions resulted in a transient increase of 10 fold over basal level of the intracellular cyclic GMP concentration. Half-maximal stimulation was obtained with 2 nM neurotensin. Under identical conditions the cyclic AMP concentration only decreased by 20-30%. These results suggest that cyclic GMP is a second messenger of neurotensin in neuroblastoma clone N1E115.     

Acute stimulation of ganglionic tyrosine hydroxylase activity by secretin,VIP and PHI

We have examined the ability of a number of neuropeptides to increase tyrosine hydroxylase (TH) activity in the superior cervical ganglion in vitro. Secretin and vasoactive intestinal peptide (VIP) both increased TH activity, whereas angiotensin II, bombesin, bradykinin, cholecystokinin octapeptide, insulin, luteinizing hormone-releasing hormone, [D-Ala², Met³]enkephalinamide, motilin, neurotensin, somatostatin, and substance P produced no effects. Secretin and VIP increased TH activity with an EC₅₀ of 5 nM and 0.5 μM, respectively. The effects of these peptides were not altered by prior decentralization of the ganglia, by addition of hexamethonium (3 mM) and atropine (6 μM), or by lowering the concentration of calcium in the medium to 0.1 mM. Addition of carbachol (3 μM) potentiated the effects of both secretin and VIP on TH activity. Several gastrointestinal peptides with structural similarities to secretin and VIP were examined for their ability to increase TH activity. Glucagon, gastric inhibitory peptide and human pancreatic tumor growth hormone-releasing factor produced no effect at a concentration of 10 μM, while PHI increased enzyme activity.     

Radiolabeled Ligands Specific for the G Protein-Coupled State of Neurotensin Receptors

Abstract: Radiolabeled analogues of neuromedin N have been prepared by acylation of the α, ε1, and ε2 amino groups of [Lys²]neuromedin N (Lys-Lys-Pro-Tyr-Ile-Leu) either with the ¹²⁵I-labeled Bolton-Hunter reagent or with N -succinimidyl[2,3-³H]propionate. The binding properties of the purified analogues toward newborn mouse brain homogenate or toward membranes of cells transitorily (COS) or permanently (AA1) transfected with the cloned rat brain neurotensin receptor cDNA were evaluated and compared with those of radiolabeled neurotensin. The α-modified analogue of [Lys²]neuromedin N behaves exactly like neurotensin in these binding experiments, whereas the ε1- and ε2-modified analogues selectively recognize the fraction of neurotensin binding sites that is sensitive to GTPγS. The proportion of neurotensin receptors coupled to GTP binding proteins is ∼50% in membranes of newborn mouse brain or of AA1 cells that respond to neurotensin by an increase of the intracellular inositol trisphosphate concentration. By contrast, membranes of transitorily transfected COS cells that do not respond to neurotensin exhibit very low levels of GTP-sensitive receptors labeled with the ε1- or ε2-modified analogues. These radiolabeled peptides offer new tools to selectively detect active neurotensin receptors.     

Differential processing of the neurotensin/neuromedin N precursor in the mouse

Posttranslational processing of the neurotensin/neuromedin N (NT/NN) precursor has been investigated in mouse brain and small intestine by means of region-specific radioimmunoassays coupled to chromatographic fractionations. In brain, total NT/NN immunoreactivity measured with a common C-terminal antiserum was 15.72 pmol/g. NT measured with an N-terminal antiserum was 9.74 pmol/g and NN measured with an N-terminal antiserum was 5.98 pmol/g. In small intestine, combined NT/NN immunoreactivity was 108.55 pmol/g, consisting of 66.37 pmol/g NT but only 0.96 pmol/g NN. Gel permeation chromatography and reverse phase HPLC revealed that the large discrepancy in the NT and NN values obtained in small intestinal extracts was due to the presence of a high molecular weight, hydrophobic peptide, which was reactive only with the common C-terminally directed antiserum. Pepsinization of this generated an immunoreactive peptide with similar chromatographic characteristics to NN. In mouse intestine, NN is only partially cleaved from the common NT/NN precursor, resulting in the presence of an N-terminally extended molecular species. This novel molecular species of neuromedin N may be the physiological mediator of certain peripheral biological effects hitherto attributed to neurotensin or neuromedin N.     

Ascorbic acid and N-acetylcysteine improve in vitro the function of lymphocytes from mice with endotoxin-induced oxidative stress.

Oxidative stress associated with reactive oxygen species (ROS) and cytokines produced by immune cells, which is involved in septic shock caused by endotoxin, can be controlled to a certain degree by antioxidants with free radical scavenging action. N-acetylcysteine (NAC) and ascorbic acid (AA) are ROS scavengers that improve the immune response, and modulate macrophage function in mice with endotoxin-caused oxidative stress. Therefore, we have investigated the in vitro effects of these antioxidants on the functions of lymphocytes from BALB/c mice with lethal endotoxic shock caused by intraperitoneal injection of E. coli lipopolysaccharide (LPS) (100 mg/kg). Adherence to tissues and chemotaxis (the earliest two functions of lymphocytes in the immune response), as well as ROS levels and TNF alpha production were determined in the presence or absence of NAC or AA (0.001, 0.01, 0.1, 1 and 2.5 mM) in lymphocytes from peritoneum, axillary nodes, spleen and thymus obtained at several times (2, 4, 12 and 24 hours) after LPS injection. Endotoxic shock decreases the chemotaxis of lymphocytes from all the above localizations and increases their adherence, TNF alpha and ROS production. These changes in lymphocyte function were counteracted by NAC and AA, bringing these functions to values near those of control animals. Our data suggest that lymphocytes are important targets of endotoxins contributing to oxidative stress by septic shock, and that antioxidants can preserve the function of lymphocytes, preventing the homeostatic disturbances caused by endotoxin.     

Differential effects of vasoactive intestinal peptide, substance P, and somatostatin on immunoglobulin synthesis and proliferations by lymphocytes from Peyer's patches, mesenteric lymph nodes, and spleen

We examined the effect of vasoactive intestinal peptide, substance P, and somatostatin on concanavalin A (1 microgram/ml)-induced lymphocyte proliferation and immunoglobulin (IgA, IgM, and IgG) synthesis by cells from spleens, Peyer's patches, and mesenteric lymph nodes. These neuropeptides (10(-7) to 10(-12) M) modulated immune responses in a dose-dependent manner. For a comparative study, neuropeptides were used at 10(-8) M concentration. Both vasoactive intestinal peptide and somatostatin significantly decreased DNA synthesis (30 to 50%), whereas substance P increased synthesis (40%) in lymphocytes from all organs tested. IgA synthesis was significantly altered by all of the neuropeptides tested, whereas IgM synthesis was less affected and IgG synthesis was virtually unchanged. Somatostatin inhibited IgA (20 to 50%) and IgM (10 to 30%) synthesis in lymphocytes from all three organs. Substance P increased IgA synthesis in mesenteric lymph nodes (50%), spleens (70%), and Peyer's patches (300%). It also increased IgM synthesis in Peyer's patches (20%) and spleens (30%), but was without effect on IgM synthesis in mesenteric lymph nodes. Vasoactive intestinal peptide increased the IgA response in mesenteric lymph nodes (20%) and spleens (30%), but inhibited IgA synthesis in lymphocytes from Peyer's patches (60%). Interestingly, in Peyer's patches, IgM synthesis was increased by vasoactive intestinal peptide (80%), whereas it was unchanged in mesenteric lymph nodes and spleen. Thus, not only did these neuropeptides have different effects on the production of different immunoglobulin isotypes, but their effect was also organ-specific. Because neuropeptides which are abundant in the intestine can modulate IgA and other immunoglobulin synthesis in vitro, they may play a significant regulatory role in mucosal immune responses in vivo.