Activation of cyclic AMP-dependent protein kinase by VIP in blood mononuclear cells

Prostaglandin E2 is a novel inducer of oncostatin-M expression in macrophages and microglia

Oncostatin-M (OSM), a pluripotent cytokine of the interleukin-6 (IL-6) family, is produced in a number of inflammatory conditions. Known sources of OSM include monocytes-macrophages and T-cells. Here we present microglia, the resident macrophages of the brain, as a source of OSM in the CNS. In this context, we describe a novel inducer of OSM, prostaglandin E(2) (PGE(2)). PGE(2) induces OSM expression in microglia, monocytes, and macrophages of human and murine origin. PGE(2) induction of OSM is mimicked by cholera toxin, an activator of stimulatory G (G(s))-proteins; by forskolin, an activator of adenylate cyclase; and by the cAMP analog, dibutyryl-cAMP. PGE(2) induction of OSM gene expression is inhibited by the adenylate cyclase inhibitor 2',5'-dideoxyadenosine, by the protein kinase A (PKA) inhibitor H-89, and by a dominant-negative PKA construct. These data indicate that PGE(2) signals via G(s)-protein-coupled receptor(s), adenylate cyclase, and PKA to induce OSM expression. Accordingly, other activators of cAMP signaling such as norepinephrine and PGE(1) induce OSM. The ability of PGE(2) to induce OSM expression was tested under more physiological conditions, using cocultures of astrocytes and monocytes. Treatment of the cocultures with IL-1beta or tumor necrosis factor-alpha (TNF-alpha) results in production of PGE(2) and OSM. PGE(2) produced in the cocultures is responsible for OSM induction, because pretreatment with indomethacin, an inhibitor of prostaglandin synthesis, as well as depletion of PGE(2), abrogate OSM expression induced by IL-1beta or TNF-alpha. These data suggest that in the CNS, OSM may be produced through collaboration of astrocytes and macrophages-microglia.

Coordinated role of vasoactive intestinal peptide and nitric oxide in cardioprotection

The present study sought to examine the interrelationship between nitric oxide (NO) and vasoactive intestinal peptide (VIP) in myocardial protection. Isolated rat hearts were perfused for 15 min with buffer only (Group I); 0.3 mM VIP (Group II); 3 mM L-arginine (a precursor of NO) (Group III); VIP and aminoguanidine (iNOS blocker) (Group IV); or L-arginine plus VIP 10-28 (VIP inhibitor) (Group V). Each heart was then made globally ischemic for 30 min followed by 2 h reperfusion. Both VIP and NO were found to provide cardioprotection during ischemia and reperfusion. However, the beneficial effects of VIP and NO were reduced by inhibition of NO and VIP, respectively, suggesting that cardioprotection by VIP is modulated by NO and vice versa. The results of this study suggested a coordinated regulation by cardioprotection by NO and VIP.

Characterization of adenylyl cyclase stimulated by VIP in rat and mouse peritoneal macrophage membranes

Vasoactive intestinal peptide (VIP) stimulated adenylyl cyclase activity in rat and mouse peritoneal macrophage membranes. GTP potentiated the stimulatory effect of VIP so that it was routinely included at 10 microM GTP. Other agents like GTP, Gpp(NH)p, GTP-gamma-S, sodium fluoride, and forskolin, at a concentration of 0.1 mM, increased the basal activity of enzyme by 3.1, 5.7, 4.7, 3.6, and 7.8-fold, respectively. The stimulation of adenylyl cyclase by VIP was time, temperature, and membrane concentration dependent. Half-maximal enzyme activation (ED50) was very similar in rat and mouse peritoneal macrophage membranes (1.5 +/- 0.1 nM and 1.0 +/- 0.1 nM, respectively). However, VIP showed more efficacy in mouse macrophages membranes (about 3.1-fold basal values) than that in rat macrophage membranes (about 2.5-fold basal values). The relative potency of several peptides upon stimulation of adenylyl cyclase activity showed the following potency in both species: VIP = PACAP38 = PACAP27 > helodermin > PHI > secretin. On the other hand, a M(r)-45 kDa alpha s subunit of Gs protein was demonstrated by both ADP-ribosylation and immunoblot in mouse and rat peritoneal macrophage membranes. The present results, together other previous, strongly suggest that VIP play an important role in the regulation of macrophage function.

Expression of vasoactive intestinal peptide binding sites in rat peritoneal macrophages is stimulated by inflammatory stimulus

Vasoactive intestinal peptide (VIP) binding to resident and stimulated-rat peritoneal macrophages was studied. No specific VIP binding was obtained with resident rat peritoneal macrophages. In contrast, VIP bound specifically to casein-elicited macrophages. The Scatchard analysis of binding data was consistent with the presence of two classes of VIP binding sites, but may represent a receptor site and internalized VIP. Both specific VIP binding and number of specific high affinity binding sites for VIP augmented progressively after sodium caseinate injection, reaching maximum at days 4-5. Macrophages obtained 1 day after injection showed a minimal specific VIP binding (0.3 +/- 0.1% of total), but cells obtained 4 days after injection showed a maximal binding to the peptide (3.1+/-0.2% of total). The number of high affinity binding sites per cell raised also progressively after sodium caseinate injection: 2650+/-301 at day 2, 4939 +/-723 at day 3, 6684+/-903 at day 4 and 9636+/-1626 at day 5 (P = 0.0035). The number of low affinity binding sites per cell exhibited the same changes. In contrast, the Kd values of both high and low affinity VIP binding sites did not vary significantly (P>0.05). These results demonstrate that VIP binding sites are only displayed by stimulated macrophages, suggesting that VIP binding sites could be considered to be a pre-activation marker in macrophages and could be used to recognize inflammatory or stimulated macrophages.

The significance of vasoactive intestinal polypeptide (VIP) in immunomodulation

Evidence for VIP influences on immune function comes from studies demonstrating VIP-ir nerves in lymphoid organs in intimate anatomical association with elements of the immune system, the presence of high-affinity receptors for VIP, and functional studies where VIP influences a variety of immune responses. Anatomical studies that examine the relationship between VIP-containing nerves and subpopulations of immune effector cells provide evidence for potential target cells. Additionally, the presence of VIP in cells of the immune system that also possess VIP receptors implies an autocrine function for VIP. The functional significance of VIP effects on the immune system lies in its ability to help coordinate a complex array of cellular and subcellular events, including events that occur in lymphoid compartments, and in musculature and intramural blood circulation. Clearly, from the work described in this chapter, the modulatory role of VIP in immune regulation is not well understood. The pathways through which VIP can exert an immunoregulatory role are complex and highly sensitive to physiological conditions, emphasizing the importance of in vivo studies. Intracellular events following activation of VIP receptors also are not well elucidated. There is additional evidence to suggest that some of the effects of VIP on cells of the immune system are not mediated through binding of VIP to its receptor. Despite our lack of knowledge regarding VIP immune regulation, the evidence is overwhelming that VIP can interact directly with lymphocytes and accessory cells, resulting in most cases, but not always in cAMP generation within these cells, and a subsequent cascade of intracellular events that alter effector cell function. VIP appears to modulate maturation of specific populations of effector cells, T cell recognition, antibody production, and homing capabilities. These effects of VIP are tissue-specific and are probably dependent on the resident cell populations within the lymphoid tissue and the surrounding microenvironment. Different microenvironments within the same lymphoid tissue may influence the modulatory role of VIP also. Effects of VIP on immune function may result from indirect effects on secretory cells, endothelial cells, and smooth muscle cells in blood vessels, ducts, and respiratory airways. Influences of VIP on immune function also may vary depending on the presence of other signal molecules, such that VIP alone will have no effect on a target cell by itself, but may greatly potentiate or inhibit the effects of other hormones, transmitters, or cytokines. The activational state of target cells may influence VIP receptor expression in these cells, and therefore, may determine whether VIP can influence target cell activity. Several reports described in this chapter also indicate that VIP contained in neural compartments is involved in the pathophysiology of several disease states in the gut and lung. Release of inflammatory mediators by cells of the immune system may destroy VIP-containing nerves in inflammatory bowel disease and in asthma. Loss of VIPergic nerves in these disease states appears to further exacerbate the inflammatory response. These studies indicate that altered VIP concentration can have significant consequences in terms of health and disease. In addition, the protective effects of VIP from tissue damage associated with inflammatory processes described in the lung also may be applicable to other pathological conditions such as rheumatoid arthritis, anaphylaxis, and the swelling and edema seen in the brain following head trauma. While VIP degrades rapidly, synthetic VIP-like drugs may be developed that interact with VIP receptors and have similar protective effects. Synthetic VIP-like agents also may be useful in treating neuroendocrine disorders associated with dysregulation of the hypothalamic-pituitary-adrenal axis, and pituitary release of prolactin.

Functional and molecular characterization of VIP receptors and signal transduction in human and rodent immune systems

In the last few decades, as a result of the interaction between different areas of research, the new interdisciplinary and exciting field of neuroimmunology has emerged. In this context, it has been demonstrated that small peptides may function in a communication network that links nervous, endocrine, and immune systems. Thus, each peptide may function as a neurotransmitter, peptide hormone, or cytokine, depending on its site of release and the target cell with which it interacts. Among these peptides, vasoactive intestinal peptide (VIP) has been shown to play a very important role in the regulation of immune function. The first stage in the action of VIP with immunocompetent cells is the binding to specific plasma membrane receptors and the generation of an intracellular signal. In this review, we focus and present data about the signal transduction pathway of VIP in both human and rodent immunocompetent cells.

Expression of VIP receptors in mouse peritoneal macrophages: functional and molecular characterization

Receptors for VIP in mouse peritoneal macrophages (MPM) were examined using [125I]labeled VIP as ligand. The receptor binding was rapid, reversible, saturable, specific, and dependent on time, pH, temperature and cell concentration. At 15 degrees C, the stoichiometric data suggested the presence of two classes of VIP receptors with Kd values of 1.05 +/- 0.2 and 66.4 +/- 11.0 nM and binding capacities of 19.2 +/- 2.8 and 706.6 +/- 172.0 fmol VIP/10(6) cells. The interaction showed a high degree of specificity, as suggested by competition experiments with various peptides structurally related to VIP as follows: VIP > helodermin > rGRF > PHI >> secretin. Glucagon, pancreastatin, somatostatin, insulin, and octapeptide of cholecystokinin (CCK 26-33) were ineffective at concentrations as high as 1 microM. VIP was a potent and efficient stimulator of cyclic AMP production in MPM. The stimulation was observed at a concentration as low as 0.01 nM VIP. Half-maximal stimulation (ED50) was observed at 1.0 +/- 0.2 nM VIP, and maximal stimulation (three-fold above basal levels) was obtained between 0.1-1 microM. The cyclic AMP system of mouse peritoneal macrophages showed a high specificity for VIP. The order of potency observed in inducing cyclic AMP production was VIP > helodermin > rGRF > PHI >> secretin. Glucagon, insulin, pancreastatin, somatostatin and octapeptide of cholecystokinin did not modify cyclic AMP levels at concentrations as high as 1 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of sulfhydryl groups in the binding of vasoactive intestinal peptide to its receptor on murine lymphocytes

The effect of sulfhydryl-containing compounds on the specific binding of the neuropeptide vasoactive intestinal peptide (VIP) to murine lymphocytes was studied. Both 2-mercaptoethanol (2ME) and dithiothreitol (DTT) inhibited VIP-binding to lymphocytes at millimolar concentrations. A sulfhydryl-containing analogue of VIP, [Cys2]VIP, was synthesized. This compound competed for the binding of [125I]VIP about 150,000 x more effectively than 2ME, but was approximately 100 x less effective than VIP itself. Both VIP and [Cys2]VIP increased intracellular cyclic AMP and inhibited the proliferative response of lymphocyte cultures to concanavalin A (ConA), but the molar potency of [Cys2]VIP on these lymphocyte activities was approximately 100 x less than that of VIP. The effects of VIP and [Cys2]VIP on intracellular cyclic AMP and ConA-stimulated proliferation were competed for by the VIP receptor antagonist [4Cl-D-Phe6,Leu17]VIP. Replacement of serine2 with L-cysteine disrupts the ability of VIP to occupy and activate lymphocyte VIP receptors. This may reflect a role of serine2 in hydrogen-bond formation during ligand-receptor interactions, or a functional role of sulfhydryl-containing residues of the VIP receptor in maintaining the integrity of the binding site of the VIP receptor on lymphocytes.

Receptors for vasoactive intestinal peptide on murine lymphocytes turn over rapidly

The interaction of the neuropeptide vasoactive intestinal peptide (VIP) with its receptors on murine mesenteric lymph node lymphocytes (MLN) has been re-examined in detail. Intact MLN actively internalize surface bound VIP. The rate constants associated with the insertion of receptors at the MLN surface, the internalization of VIP occupied and unoccupied receptors and the elimination of the peptide were determined. At 37 degrees C, MLN insert approximately 140 VIP receptors cell-1 min-1 at their surface, and the rate of internalization of occupied receptors (0.23 min-1) was much greater than that of the unoccupied receptors (0.02 min-1). Exposure of MLN to non-saturating concentrations of VIP markedly altered the expression of VIP receptors at the lymphocyte surface. The rapid turnover of VIP receptors combined with the differential clearance of occupied and unoccupied receptors from the cell surface provides a mechanism by which homologous regulation of VIP receptor expression can occur on these lymphocytes.

Synergistic action of melatonin and vasoactive intestinal peptide in stimulating cyclic AMP production in human lymphocytes

In the present study we investigated the synergistic effect of melatonin and vasoactive intestinal peptide (VIP) on cyclic AMP production in human blood lymphocytes. As shown by our group previously, VIP alone behaved as a potent activator of cyclic AMP production in human lymphocytes. On the other hand, melatonin alone did not affect the intracellular levels of cyclic nucleotide at any time or dose studied. However, when cells were incubated with melatonin plus VIP, melatonin potentiated the effect of the peptide. This effect can be observed in the presence of physiological doses of both melatonin (10-100 pM) and VIP (1-100 pM). The effect is specific for VIP because with other peptides belonging to the secretin-VIP family the effect was not observed. Results suggest that melatonin, in conjunction with VIP, may directly participate in the regulation of immune function in the human.

Melatonin potentiates cyclic AMP production stimulated by vasoactive intestinal peptide in human lymphocytes

The present paper demonstrates the effect of melatonin on cyclic AMP production in human lymphocytes from peripheral blood. Melatonin by itself did not influence cyclic AMP accumulation in these cells at any dose studied; however, the drug potentiated the effect of vasoactive intestinal peptide (VIP) on the cyclic nucleotide production. In the presence of physiological concentrations of VIP (either 1, 10 or 100 pM), melatonin potentiated cyclic AMP production. However, at high doses of VIP (either 1, 10 or 100 nM), melatonin exhibited no such effect. The results suggest that human lymphocytes are a target for melatonin and that it may participate, jointly with VIP, in the regulation of immune function.

Stimulatory effect of vasoactive intestinal peptide (VIP) on cyclic AMP production in rat peritoneal macrophages

Vasoactive intestinal peptide (VIP) stimulated cyclic AMP production in rat peritoneal macrophages. The stimulatory effect of VIP was dependent on time, temperature and cell concentration, and was potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). At 15 degrees C, the response occurred in the 0.1-1000 nM range of VIP concentrations. Half maximal stimulation of cellular cyclic AMP (ED50) was obtained at 1.2 +/- 0.5 nM VIP, and maximal stimulation (about 3-fold basal level) was obtained between 100-1000 nM. The cyclic AMP system of rat peritoneal macrophages showed a high specificity for VIP. The order of potency observed in inducing cyclic AMP production was VIP greater than rGRF greater than hGRF greater than PHI greater than secretin. Glucagon, insulin, pancreastatin and octapeptide of cholecystokinin did not modify cyclic AMP levels at concentrations as high as 1 microM. The beta-adrenergic agonist isoproterenol increased the cyclic AMP production and show additive effect with VIP. Somatostatin inhibits the accumulation of cyclic AMP in the presence of both vasoactive intestinal peptide and isoproterenol. The finding of a VIP-stimulated cyclic AMP system in rat peritoneal macrophages, together with the previous characterization of high-affinity receptors for VIP in the same cell preparation, strongly suggest that VIP may be involved in the regulation of macrophage function.

A brief survey of pineal gland-immune system interrelationships

The present paper summarizes evidence that support the hypothesis of the existence of bilateral interactions between pineal gland and the immune system. Both in vivo and in vitro experiments show that the pineal gland, via its hormone melatonin, enhances immune function. Mechanisms involved in this immunostimulatory effect are not well understood, but some evidence suggests the existence of specific binding sites for melatonin on immune cells. Moreover, the release of opioid peptides and interleukin-2 by T-helper cells may also participate in this mechanism by activating, at least natural killer activity and antibody-dependent cellular cytotoxicity. Some immune signals, i.e., gamma-interferon, may be involved in regulating pineal function, thereby representing a regulatory mechanism in the opposite direction. The physiological and clinical significance of these data remains to be studied.

Vasoactive intestinal peptide enhances phorbol myristate acetate-induced chemiluminescence in human lymphocytes

Phorbol-myristate-acetate (PMA) induced in lymphocytes the production or reactive oxygen intermediates in a process which was stimulated by the presence of vasoactive intestinal peptide (VIP) in a dose-dependent response at VIP concentrations in the range 10(-11)-10(-8) M. The dissociation constant for the high-affinity receptors of VIP agreed with the ID50 of the activation of adenylate cyclase, and the ID50 for the stimulation by VIP of PMA-induced chemiluminescence, which were close to 0.2 nM VIP. Forskolin produced in lymphocytes an effect quite similar to VIP. A comparison of the response to VIP and forskolin of lymphocytes and monocytes showed that, in contrast to forskolin, VIP failed to induce the above described effect in monocytes. A possible mechanism involving protein kinase C, which is activated by PMA, and an intracellular signal linked to VIP receptors is pointed out. This study further supports a role for VIP as a mediator in the neuroimmune system.

Characterization of functional receptors for vasoactive intestinal peptide (VIP) in rat peritoneal macrophages

Functional vasoactive intestinal peptide (VIP) receptors have been characterized in rat peritoneal macrophages. The binding depended on time, temperature and pH, and was reversible, saturable and specific. Scatchard analysis of binding data suggested the presence of two classes of binding sites: a class with high affinity (kd = 1.1 +/- 0.1 nM) and low capacity (11.1 +/- 1.5 fmol/10(6) cells), and a class with low affinity (kd = 71.6 +/- 10.2 nM) and high capacity (419.0 +/- 80.0 fmol/10(6) cells). Structural requirements of these receptors were studied with peptides structurally or not structurally related to VIP. Several peptides inhibited 125I-VIP binding to rat peritoneal macrophages with the following order of potency: VIP greater than rGRF greater than hGRF greater than PHI greater than secretin. Glucagon, insulin, somatostatin, pancreastatin and octapeptide of cholecystokinin (CCK 26-33) were ineffective. VIP induced an increase of cyclic AMP production. Half-maximal stimulation (ED50) was observed at 1.2 +/- 0.5 nM VIP, and maximal stimulation (3-fold above basal levels) was obtained between 0.1-1 microM. Properties of these binding sites strongly support the concept that VIP could behave as regulatory peptide on the macrophage function.

Signal transduction through the vasoactive intestinal peptide receptor stimulates phosphorylation of the tyrosine kinase pp60c-src

The present study demonstrates that signal transduction through a receptor lacking intrinsic tyrosine protein kinase activity involves a rapid and potent phosphorylation of a non-receptor tyrosine protein kinase in the membranes. Vasoactive intestinal peptide (VIP) stimulates phosphorylation of a membrane protein with a M.W. of 56 KD (pp60) in the cultured chick embryonic retinal pigment epithelium. VIP stimulates phosphorylation of the pp60 with such efficiency and potency that the maximal phosphorylation has been observed at the earliest time (3 minutes at 1 x 10(-6)M VIP) and the lowest concentration (1 x 10(-11)M for 20 minutes) examined. Western blot analysis with a monoclonal antibody anti-pp60src (GD11, Parsons et al., J. Virol. 51, 272-282, 1984) indicates that the pp60 is the pp60c-src, a normal cell oncogene product with intrinsic tyrosine protein kinase activity.

Effect of neuropeptides and monoamines on lymphocyte activation

Neuropeptides and monoamines have been found in tissues where immune reactions are initiated such as the skin, gut, and respiratory tract, and in these tissues neuropeptides and monoamines might be involved in the regulation of lymphocyte activation. Studies both in in vitro and in vivo showing that various neuropeptides and monoamines may influence reactions such as T lymphocyte proliferation, B lymphocyte proliferation, and antibody synthesis, lymphocyte migration, and cytotoxicity will be reviewed.

Vasoactive intestinal peptide-containing nerves in Peyer's patches

Vasoactive intestinal peptide (VIP) is a neuropeptide that is well represented in the gut tract. Previous work has demonstrated that murine T lymphocytes have high-affinity specific receptors for VIP and has implicated their interaction with VIP in the control of T-cell migration into Peyer's patches in vivo. It was postulated that this effect was mediated by interactions in the vicinity of the specialized endothelium of the postcapillary venules of Peyer's patches. We report the localization of VIP-like immunoreactivity in mouse Peyer's patches. Immunohistochemical staining was performed with heterologous antiserum against VIP using the avidin-biotin-peroxidase complex technique. VIP positivity was present near vessels of various sizes and in close proximity to small caliber vessels lined with specialized polygonal endothelial cells. These findings provide an anatomical basis for the concept that VIP may be available as a local neurophysiological signal during the migration of lymphocytes from the blood into Peyer's patches.

Effects of fasting and refeeding on vasoactive intestinal peptide binding to rat blood mononuclear cells

The effect of acute and chronic starvation on vasoactive intestinal peptide (VIP) binding to rat blood mononuclear cells was studied. A short-term (1 day) fasting period did not induce significant changes in VIP binding. Longer periods of fasting (3 and 5 days) elicited an increase in VIP binding. This increase was due to an increase in affinity of both the high and the low affinity binding sites rather than to changes in binding capacity. Refeeding of fasted animals resulted in a decrease in VIP binding, reaching similar values to those of the control groups.

Interaction of a bovine thymic peptide extract with vasoactive intestinal peptide (VIP) receptors

Bovine thymic peptide extract (1-100 micrograms/ml) is shown to completely inhibit the binding of [125I]VIP to rat blood mononuclear cells, lymphoid cells of spleen, and liver plasma membranes. In the three models, the bovine thymic peptide extract inhibits [125I]VIP binding with a potency that is 4000-7000 times lower than that of the native VIP, on a weight basis. In rat liver plasma membranes, the bovine thymic peptide extract stimulates adenylate cyclase with a maximal efficiency that is similar to that of VIP. At maximal doses, VIP and thymic peptide extract do not exert an additive effect on adenylate cyclase, suggesting that the activation of the enzyme by the bovine thymic peptide extract occurs through VIP receptors. Finally, no VIP-like immunoreactivity was detected in the thymic peptide extract using an antiserum raised against mammalian VIP. All these data suggest the presence in the bovine thymic peptide extract of a new substance which behaves as a VIP agonist in rat.

Interaction of vasoactive intestinal peptide (VIP) with rat lymphoid cells

Receptors for vasoactive intestinal peptide (VIP) have been characterized in rat lymphoid cells. The interaction of [125I] VIP with blood mononuclear cells was rapid, reversible, specific and saturable. At apparent equilibrium, the binding of [125I] VIP was competitively inhibited by native VIP in the 0.01-100 nM range concentration. The binding data were compatible with the existence of two classes of receptors: a high-affinity class with a Kd = 0.050 +/- 0.009 nM and a low binding capacity (2.60 +/- 0.28 fmol/10(6) cells), and a low-affinity class with a Kd = 142 +/- 80 nM and a high binding capacity (1966 +/- 330 fmol/10(6) cells). Secretin, glucagon, insulin and somatostatin did not show any effect at a concentration as high as 100 nM. With spleen lymphoid cells, stoichiometric studies were performed. The binding data were compatible with the existence of two classes of receptors: a high-affinity class with a Kd = 0.100 +/- 0.033 nM and a low binding capacity (4.60 +/- 1.07 fmol/10(6) cells), and low-affinity class with a Kd = 255 +/- 110 nM and high binding capacity (2915 +/- 1160 fmol/10(6) cells). With thymocytes, no binding was obtained under different conditions.

Vasoactive intestinal peptide (VIP) binding to solubilized material from rat liver plasma membranes

A non-ionic detergent such as Lubrol-PX extracts in soluble form the VIP-binding structures of rat liver plasma membranes. Detergent-solubilized proteins bind specifically [125I]VIP and the complex tracer-protein is identified by the use of Sepharose 6B columns. The interaction is only possible in the absence of detergent (below 0.001%) and is inhibited by native peptide. A molecular weight of about 80,000 was estimated for VIP-binding proteins by reference to a series of globular markers of proteins. Binding to VIP soluble proteins is specific and dependent on time as studied by the Hummel and Dreyer (Biochim. Biophys. Acta 63:530-532, 1962) assay.

Interaction of vasoactive intestinal peptide (VIP) with human peripheral blood lymphocytes: specific binding and cyclic AMP production

VIP binding sites and cyclic AMP production by the peptide have been studied in human blood mononuclear cells before and after selective depletion of or enrichment for T-lymphocytes, B-lymphocytes-K-NK cells and monocytes. The specifically bound 125I-labelled VIP correlated significantly with the presence of B-lymphocytes and/or cells of K-NK system. The stoichiometric data were compatible with the existence of two classes of binding sites. T-lymphocytes and monocytes did not show binding of the tracer. The cyclic AMP production stimulated by VIP correlated significantly with the presence of B-lymphocytes and/or K-NK cells.

The interaction of vasoactive intestinal peptide (VIP) with isolated bovine thyroid plasma membranes

The binding of vasoactive intestinal peptide (VIP) and stimulation of adenylate cyclase were studied in bovine thyroid plasma membranes. The binding depended on time, temperature and was saturable and specific. Binding studies suggested the presence of two classes of binding sites: a class with high affinity (Kd = 13 nM) and low capacity (6411 sites/pg), and a class with low affinity (Kd = 480 nm) and high capacity (105,300 sites/pg) at 15 degrees C. Secretin, glucagon, insulin and somatostatin did not displace the tracer from the membranes. VIP stimulated cyclic AMP production. Maximal cyclic AMP production (2-fold above basal values) was observed with 100 nM VIP and half-maximal response was obtained at 5 nM VIP at 15 degrees C.