Effect of Cyclic Nucleotides on DNA Synthesis in Mouse Lymphoid Cells

The effect of eight cyclic purine and cyclic pyrimidine nucleotides on DNA synthesis on mouse lymphoid cells was investigated. Two out of eight compounds tested, namely 2',3'-cyclic guanosine monophosphate (2',3'-cGMP) as well as 3',5'-cyclic guanosine monophosphate (3',5'-cGMP), stimulate thymidine incorporation in all types of lymphocytes tested. The stimulatory activity of the cyclic guanosine nucleotides as well as the effects of lectins could be antagonized by 3',5'-cyclic adenosine monophosphate (3',5'-cAMP). 2',3'-cGMP seems to stimulate preferentially mature T-cells while 3',5'-cGMP preferentially acts on B-cells.     

Human Leucocyte Migration Inhibitory Factor (LIF)

The cyclic nucleotides guanosine 3',5'-cyclic monophosphoric acid (3',5'-cGMP) and cytidine 2',3'-cyclic monophosphoric acid (2',3'-cCMP) but not cyclic phosphodiesters derived from the bases adenine and uracil preserved LIF activity against the blocking effect of the serine protease inhibitor phenylmethylsulphonyl fluoride (PMSF). Phosphomonoesters derived from guanosine and cytidine as well as 2',3'-cGMP and 3',5'-cCMP were all inactive, indicating specificity for phosphodiester bonds and their respective positions in the two active nucleotides. The protection afforded by 3',5'-cGMP and 2',3'-cCMP was dose dependent. Thus, using 10(-3) M PMSF, 3',5'-cGMP was active at concentrations higher than 10(-5) to 10(-4) M, and 2',3'-cCMP at concentrations higher than 3 X 10(-4) to 10(-3) M. The more pronounced LIF-inhibitory effect obtained by increased concentrations of PMSF could be overcome by raising the levels of the nucleotides, indicating that the interactions between PMSF and the nucleotides with LIF were mutally exclusive. The possibility that 3',5'-cGMP and perhaps 2',3'-cCMP function as modulators of LIF is discussed, and models for the function of this lymphokine are proposed.     

The role of extracellular Ca2+ and cyclic nucleotides in the mechanism of enzyme secretion from the cat pancereas

The role of Ca2+ in protein secretion from the isolated perfused cat's pancreas, the effect of the dibutyryl analogues of cAMP and cGMP, and the interrelation of Ca2+ and the nucleotides were studied. The following results were obtained: 1. Pancreatic enzyme secretion can be elicited by CaCl2 injections into the pancreatic arteries and is linearily related to the peak Ca2+ concentration in the effluent perfusate. Different background Ca2+ concentrations in the perfusate (3 mM or 0.125 mM) do not disturb this relation, indicating that no adaptation occurs. The effect of Ca2+ injections is of the same magnitude as that evoked by the hormones pancreozymin or acetylcholine. 2. Injections of Ca2+ potentiate the effects of dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP), dibutyryl guanosine 3',5'-cyclic monophosphate (dbcGMP) or theophylline. 3. Infusion of low doses of pancreozymin increases the Ca2+ effect. The findings indicate that extracellular Ca2+ is involved in the mechanism of enzyme secretion and that Ca2+ and cyclic nucleotides have a synergistic action on the target.     

Effect of Cyclic Nucleotides, Isoproterenol and Cholera Toxin on DNA Synthesis Triggered by Mitogens

The effect of cyclic nucleotides, isoproterenol and cholera toxin on phytohaemagglutinin (PHA), concanavalin A (Con A) and anti-allotype-induced rabbit lymphoid cell proliferation was examined. Cholera toxin in concentrations ranging from 10(-8) microgram to 1 microgram per culture inhibited DNA synthesis, triggered by PHA, Con A and nocardia water-soluble mitogen (NWSM). It had the opposite effect on stimulation with antibodies directed against allotypic specificities of the immunoglobulin light chains: over the entire range of tested concentrations, cholera toxin stimulated DNA synthesis triggered by antibodies to Ab4, Ab5, Ab9 and to Aa1 allotypic specificities. Relatively high concentrations of dibutyryl adenosine 3':5'-cyclic monophosphate (cAMP) and isoproterenol (10(-3) M) inhibited mitogen-stimulated thymidine incorporation; lower concentrations (10(-9) M) had an enhancing effect. A similar enhancing effect was observed when high (10(-3) M) concentrations of dibutyryl guanosine 3':5'-cyclic monophosphate (cGMP) were used.     

Signaling pathway and pepsinogen secretion in Helicobacter pylori-infected human gastric adenocarcinoma

Although in vitro studies have suggested that Helicobacter pylori not only attaches to cultured cells but also induces signal transduction events in host cells, the underlying mechanism of H. pylori action has yet to be fully investigated. In the present study, a cytotoxin-positive H. pylori was used to infect and examined for its effect on the stimulation of second messengers in human gastric adenocarcinoma (AGS). Results showed that H. pylori increased cytosolic free calcium concentration [Ca2+]i in host cells in a dose-dependent manner. The increase of [Ca2+]i was due to release from the intracellular Ca2+ store as well as entry to the extracellular Ca2+. H. pylori infection on host cells was also found to induce the generations of inositol phosphates, adenosine 3', 5'-cyclic monophosphate, and guanosine 3',5'-cyclic monophosphate, and to stimulate the secretion of pepsinogen.     

Human Leukocyte Migration Inhibitory Factor (LIF)

Recently reported experiments suggest that human leukocyte migration inhibitory factor (LIF) has properties of an esterase and a protease with substrate specificities directed against arginine esters and amides. Also reported previously, the synthetic phosphodiester bis-p-nitrophenyl phosphate (BNPP) but not various phosphomonoesters preserve LIF activity in the presence of the serine esterase inhibitor phenylmethylsulfonyl fluoride (PMSF). In this paper I demonstrate that guanosine 3'5'-cyclic monophosphoric acid (3',5'-cGMP), a naturally occurring phosphodiester, at concentrations in excess of 10(-5)M also protects LIF against PMSF inactivation. The effect seems specific for the diester bond, its position in the nucleotide, and the guanine base. The possibility that LIF may be a multifunctional or an allosteric enzyme regulated by 3',5'-cGMP is discussed.     

Guanosine 3',5'-cyclic monophosphate mediated inhibition of cell death induced by nerve growth factor withdrawal and beta-amyloid: protective effects of propentofylline

Apoptotic cell death has been implicated in Alzheimer's disease pathology and amyloid peptide induced neurotoxicity. We investigated the survival promoting effects of Propentofylline in two models of apoptotic cell death, nerve growth factor withdrawal and beta-amyloid mediated cell death in nerve growth factor differentiated rat pheochromocytoma cell lines. The increase in cell death as measured by lactate dehydrogenase release in response to nerve growth factor withdrawal was suppressed by nitric oxide donor S-nitroso-N-acetylpenicillamine (12.5 to 200 microM) and by 8-bromoguanosine-3',5'-cyclic monophosphate (1.25 to 10mM). Both agents decreased cell death mediated by 25 microM beta-amyloid, suggesting that the protective mechanism involves guanosine -3', 5'-cyclic monophosphate. In support of this hypothesis we can show that S-nitroso-N-acetylpenicillamine increases intracellular levels of guanosine -3',5'-cyclic monophosphate in pheochromocytoma cell lines 3 to 8 fold.Propentofylline, a phosphodiesterase inhibitor, has previously demonstrated neuroprotective activity in stroke models and is a potential candidate for therapeutic treatment in neurodegenerative diseases. The present findings support this claim by providing evidence that Propentofylline has protective effects in both nerve growth factor withdrawal and beta-amyloid mediated cell death. Lactate dehydrogenase release was significantly reduced and caspase-3-like activity was attenuated after cotreatment with Propentofylline. Furthermore Propentofylline dose responsively increases intracellular guanosine-3',5'-cyclic monophosphate levels over the same dose range that provided protection. We hypothesized that guanosine-3',5'-cyclic monophosphate is a key mediator of neuroprotection under these conditions.     

Nanomolar cyclic adenosine and guanosine monophosphates stimulate macrophage colony-stimulating factor responsiveness by murine transitional progenitors.

Both 3':5' cyclic adenosine monophosphate (cAMP) and 3':5' cyclic guanosine monophosphate (cGMP) stimulated colony-stimulating factor 1 (CSF-1)-dependent colony formation by murine two-signal-dependent progenitors without influencing colony formation by committed CSF-1-responsive progenitors. The stimulatory effect was optimal at 10(-9) M and did not diminish with increasing concentrations of the cyclic nucleotides. The membrane-permeating analogs dibutyryl cAMP and 8-Br-cGMP similarly augmented colony formation by the transitional progenitors at 10(-9) M; however, with increasing concentration, enhancement diminished with eventual inhibition of total colony formation at micromolar concentrations. Stimulation by the two cyclic nucleotides was mutually incompatible. The results indicate that physiological levels of extracellular cyclic nucleotides may significantly influence myelopoiesis. Furthermore, the results introduce the interesting possibility that stimulation, unlike inhibition, may be initiated through an extracytoplasmic mechanism that does not require direct activation of cytoplasmic cyclic nucleotide-dependent protein kinases.     

A possible role for calcium in cyclic nucleotide mediated fluid secretion

This article suggests that calcium acts as an intermediate for intestinal fluid secretion mediated by adenosine-3':5'-cyclic monophosphoric acid (cAMP) and guanosine -3':5-'cyclic monophosphoric acid (cGMP). It is hypothesized that microbial enterotoxins disrupt the normal interrelationships between calcium and cyclic nucleotides, thereby leading to adverse biological effects. It is further proposed that the inhibitory effect of chlorpromazine on calmodulin accounts for the ability of this drug to inhibit enterotoxins which separately elevate cAMP or cGMP concentrations.     

Cyclic nucleotides in the rat caudate-putamen complex: histochemical characterization and effects of deafferentation and kainic acid infusion

Guanosine 3′,5′-cyclic monophosphate (cyclic guanosine monophosphate) and adenosine 3′,5′-cyclic monophosphate (cyclic adenosine monophosphate) were characterized immunohistochemically in the striatum of the rat. Cyclic guanosine monophosphate was associated primarily with fibrillar elements, some of which derived from cell bodies having maximum soma dimensions of 6–10 μm. Cyclic adenosine monophosphate was found primarily in relationship to oval or triangular somata 12–20 μm in maximum extent. Radio-frequency or suction ablations in brain regions—the ventral diencephalon, cortex and thalamus—providing or containing afferents to the caudate-putamen complex produced no effect on histochemical staining patterns or biochemically assessed levels of the two cyclic nucleotides. Loss of immunofluorescence to the two cyclic nucleotides was observed microscopically, however, following intrastriatal infusion of kainic acid; cyclic nucleotides in the non-injected striatum were unchanged. The latter histochemical results could not be corroborated biochemically. Radioimmunoassays showed no net effect of kainic acid on levels of the two cyclic nucleotides in the infused caudateputamen nucleus, whereas levels of these two chemical compounds were increased to 170–219% in the contralateral striatum.It was concluded that, as assessed histochemically, (1) cyclic guanosine monophosphate is primarily associated with glial cells and/or ‘glial-like’ neurons whereas cyclic adenosine monophosphate is found in relationship to neurons and (2) the striatal tissue elements containing these two cyclic nucleotides are organized primarily within the caudate-putamen complex. In addition, (3) immunohistochemical procedures for cyclic nucleotides may assay only tightly bound stores of cyclic nucleotides, whereas biochemical methods may measure both labile and stable pools. This last consideration permits reconciliation of differing results obtained with histochemical and biochemical techniques following intrastriatal infusion of kainic acid.     

A rapid and economical method of preparing radioiodinated cyclic nucleotide derivatives for use in radioimmunoassays

2'-O-succinyladenosine 3':5'-cyclic monophosphate tyrosyl methyl ester (ScAMP-TME) and 2'-O-succinylguanosine 3':5'-cyclic monophosphate tyrosyl methyl ester (ScGMP-TME) were radioiodinated using chloramine T and Na125I. The resulting radiolabeled cyclic nucleotide derivatives, ScAMP-125I-TME and ScGMP-125I-TME, were subsequently purified by reverse-phase chromatography on Sep-Pak C18 cartridges (Waters Associates, Milford, MA) and tested as tracers in sensitive radioimmunoassays for cAMP and cGMP, respectively. Purified ScAMP-125I-TME and ScGMP-125I-TME functioned in the respective radioimmunoassays for up to 12 weeks when suspended in a 1:1 (v:v) mixture of n-propanol and 20 mM sodium acetate, pH 6.0. Thus, this purification method enables rapid and economical preparation of tracers for cyclic nucleotide radioimmunoassays. Furthermore, our findings suggest that reverse-phase chromatography may be applicable to the purification of other small polar molecules to which tyrosyl groups have been added for the purpose of radioiodination.     

Alterations of the expression and activity of midbrain nitric oxide synthase and soluble guanylyl cyclase in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

The study was aimed at investigating the expression and the activity of neuronal nitric oxide synthase, and of soluble guanylyl cyclase and phosphodiesterase activities that regulate guanosine 3',5'-cyclic monophosphate level in the midbrain, in a mouse model of PD using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine injections. Adult male mice of the C57/BL strain were given three i.p. injections of physiological saline or three i.p. injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine solution in physiological saline at 2 h intervals (summary 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine dose: 40 mg/kg), and were killed 3, 7, or 14 days later. mRNA, protein level, and/or activities of neuronal nitric oxide synthase, soluble guanylyl cyclase, phosphodiesterase and guanosine 3',5'-cyclic monophosphate were determined. Immunohistochemistry showed about 75% decrease in the number of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta. Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine showed increased midbrain guanylyl cyclase and total nitric oxide synthase activities at 3, 7, and 14 days post-treatment. The specific neuronal nitric oxide synthase inhibitor 7-nitroindazole (10 microM) and the specific inducible nitric oxide synthase inhibitor 1400W (10 microM) inhibited the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced excess in nitric oxide synthase activity by 63-70 and 13-25%, respectively. The increases in total midbrain nitric oxide synthase activity were accompanied by elevated guanosine 3',5'-cyclic monophosphate, enhanced expression of neuronal nitric oxide synthase and of the beta1 subunit of guanylyl cyclase at both mRNA and protein levels that persisted up to the end of the observation period, and by enhanced neuronal nitric oxide synthase and guanylyl cyclase beta1 immunoreactivities in substantia nigra pars compacta 7 and 14 days after the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment. The increases in guanylyl cyclase activity were found to occur exclusively due to increased maximal enzyme activity. No 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced change in phosphodiesterase activity has been detected in any brain region studied. 7-Nitroindazole prevented a significant increase in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced midbrain guanosine 3',5'-cyclic monophosphate level and neurodegeneration of dopaminergic neurons. These results raise the possibility that the nitric oxide/guanylyl cyclase/guanosine 3',5'-cyclic monophosphate signaling pathway may play a role in maintaining dopaminergic neurons function in substantia nigra pars compacta.     

Acetylcholine inhibits positive inotropic effect of cholera toxin in ventricular muscle

Acetylcholine (ACh, 10(-6) M) had no effect on basal adenylate cyclase activity (3.4 +/- 0.56 pmol cyclic AMP . min-1 . mg wet wt-1), adenosine 3',5'-cyclic monophosphate (cyclic AMP) content (0.88 +/- 0.09 pmol/mg wet wt), or the force of contraction in paced (2.5 Hz) chick embryo right ventricles superfused with Tyrode solution. After 60-180 min of superfusion in the presence of cholera toxin (5 x 10(-6) g/ml), adenylate cyclase activity (1.7 times), cyclic AMP content (2.4 times), and contractility (2.4 times) had increased significantly above basal levels. ACh reversed the positive inotropic effect of cholera toxin but did not change the increased activity of adenylate cyclase and content of cyclic AMP obtained in cholera toxin. Stimulation of adenylate cyclase by isoproterenol (ISO) was inhibited by ACh in the absence and presence of cholera toxin. ACh did not change guanosine 3',5'-cyclic monophosphate (cyclic GMP) content in the absence or presence of cholera toxin. Cholera toxin has actions on chick embryo ventricle similar to those of the beta-adrenergic agonist, ISO, and the phosphodiesterase inhibitor, isobutylmethylxanthine. The ability of ACh to reverse the positive inotropic effect of cholera toxin without preventing the accumulation of cyclic AMP may involve the prevention or reversal of cyclic AMP-dependent phosphorylation. In this regard, reduction of Ca2+ influx through voltage-sensitive membrane channels may be an essential component of muscarinic inhibition.     

Cyclic AMP levels and cellular kinetics during maturation of human promyelocytic leukemia cells

Differentiation of human promyelocytic leukemia cells (HL-60) in response to several classes of inducing agents is characterized by the sequential appearance of granulocytic or monocytic markers. Compounds that increase intracellular cAMP in HL-60 cells induce a program of maturation in which cells demonstrate early functional phagocytic properties. Cyclic nucleotide metabolism was studied during monocytic and granulocytic differentiation of the HL-60 cell line. In synchronous and nonsynchronous cell cultures, cyclic AMP levels were raised 300-fold or 25-fold in response to N6, O2-dibutyryl adenosine 3':5'-cyclic monophosphate or the combination of prostaglandin E2 and theophylline, respectively. No reproducible changes in intracellular adenosine 3':5'-cyclic monophosphate levels occurred in response to retinoic acid or dimethyl sulfoxide, suggesting that changes in adenosine 3':5'-cyclic monophosphate levels alone do not mediate cell maturation induced by these compounds. Agents that increased intracellular cyclic AMP in HL-60 cells slowed the progress through the S and G2-M phase of the cell cycle, whereas other agents such as dimethyl sulfoxide stimulated cells through this same period.     

Induction of hippocampal LTD requires nitric-oxide-stimulated PKG activity and Ca2+ release from cyclic ADP-ribose-sensitive stores.

Long-term depression (LTD) of synaptic transmission can be induced by several mechanisms, one thought to involve Ca2+-dependent activation of postsynaptic nitric oxide (NO) synthase and subsequent diffusion of NO to the presynaptic terminal. We used the stable NO donor S-nitroso-N-acetylpenicillamine (SNAP) to study the NO-dependent form of LTD at Schaffer collateral-CA1 synapses in vitro. SNAP (100 microM) enhanced the induction of LTD via a cascade that was blocked by the N-methyl-D-aspartate receptor antagonist D-2-amino-5-phosphonopentanoic acid (50 microM), NO guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (10 microM), and the PKG inhibitor KT5823 (1 microM). We further show that LTD induced by low-frequency stimulation in the absence of SNAP also is blocked by KT5823 or Rp-8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphorothioate (10 microM), cyclic guanosine 3',5' monophosphate-dependent protein kinase (PKG) inhibitors with different mechanisms of action. Furthermore SNAP-facilitated LTD was blocked when release from intracellular calcium stores was inhibited by ryanodine (10 microM). Finally, two cell-permeant antagonists of the cyclic ADP-ribose binding site on ryanodine receptors also were able to block the induction of LTD. These results support a cascade for induction of homosynaptic, NO-dependent LTD involving activation of guanylyl cyclase, production of guanosine 3',5' cyclic monophosphate and subsequent PKG activation. This process has an additional requirement for release of Ca2+ from ryanodine-sensitive stores, perhaps dependent on the second-messenger cyclic ADP ribose.     

Activation of inwardly rectifying K+ channel in OK proximal tubule cells involves cGMP-dependent phosphorylation process

The inwardly rectifying K+ channel with an inward conductance of about 90 pS in the surface membrane of cultured opossum kidney proximal tubule (OKP) cell is activated by cyclic AMP-dependent protein kinase (PKA). In this study, we further examined the involvement of the guanosine 3',5'-cyclic monophosphate (cGMP)-dependent process in modulation of this K+ channel by using the patch-clamp technique. In cell-attached patches, channel activity was increased by the application of either N2, 2'-O-dibutyrylguanosine 3',5'-cyclic monophosphate (DBcGMP, 100 microM) or 8-bromoguanosine 3',5'-cyclic monophosphate (8BrcGMP, 100 microM), and it was inhibited by KT5823 (10 microM), a membrane-permeable specific inhibitor of cGMP-dependent protein kinase (PKG). The effect of DBcGMP on channel activity was abolished by the pretreatment of cells with KT5823 (10 microM), but it was observed in the presence of KT5720 (200 nM), a specific inhibitor of PKA. Furthermore, atrial natriuretic peptide (ANP, 10 nM) increased channel activity, which was also prevented by the application of KT5823 (10 microM). In inside-out patches, ATP (3 mM) was required to maintain channel activity, which was inhibited by KT5823 (10 microM), but it was not increased by cGMP (100 microM) alone. The channel activity was increased by the coapplication of PKG (500 U/ml) and cGMP (100 microM). These results suggest that cGMP activates the inwardly rectifying K+ channel in OKP cells through PKG-mediated phosphorylation processes independent of PKA-mediated processes, and that ANP is an agonist which stimulates PKG-mediated processes in the proximal tubule cell. Furthermore, it is suggested that the ATP-dependent channel activity in inside-out patches is maintained at least in part by PKG, which is the membrane-bound catalytic domain.     

Interleukin II increases cyclic GMP levels in immature thymocytes and mitogen-primed T-lymphocytes

Interleukin II, also called T-cell growth factor, induces proliferation of immature peanut agglutinin positive murine thymocytes (PNA+) and renders them responsive to concanavalin A. It also, as shown by others, provides a second signal to induce phytohemagglutinin-primed mature human T-lymphocytes to enter DNA synthesis. Both actions are associated with early increases (2-60 min) in cellular levels of cyclic 3'5' guanosine monophosphate (cyclic GMP) without change of cyclic 3'5' adenosine monophosphate (cyclic AMP) levels. Cyclic GMP is postulated to represent part of the mechanism by which IL-2 acts.     

In vitro effect of thymic epithelial culture supernate on cyclic GMP levels in rabbit platelets

When supernatants of thymic epithelial cell cultures (STEC) or thymosin fraction 5 were incubated with washed platelets (37 degrees C for 30 min), the levels of platelet guanosine 3',5'-cyclic monophosphate (cyclic GMP) were increased in a dose-dependent manner. In contrast the supernatants from Chang, HeLa, or HCC-M cell cultures did not significantly affect the levels of intracellular cyclic GMP. The increment of intracellular cyclic GMP levels following treatment with STEC increased with longer incubation times until a plateau was reached at 30 min. This activity of STEC was found in fractions with a molecular weight below 10,000 daltons. Contents of guanine and guanosine in STEC were lower than those observed in other culture supernatants. STEC did not affect guanylate cyclase activity in platelets, but significantly inhibited cyclic GMP phosphodiesterase activities in platelet soluble and membrane fractions. Thymosin fraction 5 inhibited the phosphodiesterase activity of the soluble but not the membrane fraction.     

Enzyme immunoassays for the estimation of adenosine 3',5' cyclic monophosphate and guanosine 3',5' cyclic monophosphate in biological fluids.

Simple, rapid and sensitive competitive enzyme immunoassays for the estimation of adenosine 3',5' cyclic monophosphate (cAMP) and guanosine 3',5' cyclic monophosphate (cGMP) in human plasma and urine are described. Specific antisera to each nucleotide were raised in rabbits by immunization with succinyl cyclic nucleotide--human serum albumin conjugates. For the assay, specific antibodies were incubated with a mixture of succinyl cyclic nucleotide labelled with horseradish peroxidase together with unlabelled standard or sample. The antibody-bound enzyme conjugate was separated from free hapten by anti-rabbit (IgG) sera immobilized to a microtitre plate. Activity of the bound enzyme conjugate was determined with tetramethylbenzidine. The assays were capable of detecting levels as low as 2 fmol of cAMP and cGMP. Good correlations were obtained between values generated by enzyme immunoassay and radioimmunoassay.     

Tea catechin, (-)-epigallocatechin gallate, causes membrane depolarizations of myenteric neurons in the guinea-pig small intestine

Chicken and mammalian (human/porcine/rat) vasoactive intestinal peptides (VIP; 0.01-3 microM), whose structures differ by four amino acid residues in 11, 13, 26 and 28 positions, were compared with respect to their ability to stimulate adenosine 3',5'-cyclic monophosphate (cyclic AMP) formation in the hypothalamus and cerebral cortex of chick and rat. In four tested biological systems, the chicken VIP appeared to be significantly more potent in evoking cyclic AMP response than its mammalian counterpart, the differences were more pronounced in the chick tissues, particularly in the hypothalamus, where the mammalian peptide produced only weak (but significant) effect at the highest used dose, i.e. 3 microM. Pituitary adenylate cyclase-activating polypeptide, a VIP-like peptide, applied as a reference drug at 0.1 microM, strongly stimulated cyclic AMP formation in all tested systems. The data demonstrate significant quantitative differences in biological activity between mammalian and non-mammalian peptides tested in brain tissue of chicks and rats, indicating that usage of the mammalian VIP in at least 'avian' studies may lead to some false conclusions.