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J W Daly

Publications and source records attributed to J W Daly.

At least 55 records · Page 3Linked to original sources
PubMed1995

Chronic NMDA receptor stimulation: therapeutic implications of its effect on adenosine A1 receptors.

It is known that stimulation of adenosine A1 receptors has a modulatory effect on the excitability of postsynaptic NMDA receptors. Conversely, acute stimulation of NMDA receptors results in release of adenosine via calcium-independent mechanisms. These findings indicate a close functional relationship between these receptors. It is, therefore, possible that chronic, low level stimulation of the NMDA receptor may have a negative impact on these modulatory processes. To investigate this possibility, we have subjected C57BL mice either to an acute injection of a N6-cyclopentyladenosine (CPA, 0.01 mg/kg) or deoxycoformycin (1 mg/kg) followed by a convulsant dose of N-methyl-D-aspartate (NMDA) (60 mg/kg) or to chronic, low level (20 mg/kg i.p. daily) exposure to NMDA for 8 weeks. One day after the last injection of NMDA, animals were injected either with a convulsant dose of NMDA alone, or with either CPA at 0.001 or 0.01 mg/kg, or with 1 mg/kg deoxycoformycin followed 15 min later by 60 mg/kg NMDA. Neither CPA nor deoxycoformycin were protective when NMDA was given acutely at 60 mg/kg. Chronic treatment with NMDA alone or chronic administration of NMDA followed by 0.001 mg/kg CPA had no significant effect on mortality following a convulsant dose of NMDA. However, when the chronic regimen of NMDA was followed by either 0.01 mg/kg CPA or 1 mg/kg deoxycoformycin, mortality was reduced to 10% (CPA), or eliminated completely (deoxycoformycin). Moreover, combination of chronic NMDA treatment with either CPA (both doses) or deoxycoformycin produced a significant improvement in other measures, i.e., seizure onset, intensity of neurological impairment, and extension of time to death.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1995

The chemistry of poisons in amphibian skin.

Poisons are common in nature, where they often serve the organism in chemical defense. Such poisons either are produced de novo or are sequestered from dietary sources or symbiotic organisms. Among vertebrates, amphibians are notable for the wide range of noxious agents that are contained in granular skin glands. These compounds include amines, peptides, proteins, steroids, and both water-soluble and lipid-soluble alkaloids. With the exception of the alkaloids, most seem to be produced de novo by the amphibian. The skin of amphibians contains many structural classes of alkaloids previously unknown in nature. These include the batrachotoxins, which have recently been discovered to also occur in skin and feathers of a bird, the histrionicotoxins, the gephyrotoxins, the decahydroquinolines, the pumiliotoxins and homopumiliotoxins, epibatidine, and the samandarines. Some amphibian skin alkaloids are clearly sequestered from the diet, which consists mainly of small arthropods. These include pyrrolizidine and indolizidine alkaloids from ants, tricyclic coccinellines from beetles, and pyrrolizidine oximes, presumably from millipedes. The sources of other alkaloids in amphibian skin, including the batrachotoxins, the decahydroquinolines, the histrionicotoxins, the pumiliotoxins, and epibatidine, are unknown. While it is possible that these are produced de novo or by symbiotic microorganisms, it appears more likely that they are sequestered by the amphibians from as yet unknown dietary sources.

Amphibian Venoms↗
PubMed1995

The amphiphilic peptide adenoregulin enhances agonist binding to A1-adenosine receptors and [35S]GTP gamma S to brain membranes.

1. Adenoregulin is an amphilic peptide isolated from skin mucus of the tree frog, Phyllomedusa bicolor. Synthetic adenoregulin enhanced the binding of agonists to several G-protein-coupled receptors in rat brain membranes. 2. The maximal enhancement of agonist binding, and in parentheses, the concentration of adenoregulin affording maximal enhancement were as follows: 60% (20 microM) for A1-adenosine receptors, 30% (100 microM) for A2a-adenosine receptors, 20% (2 microM) for alpha 2-adrenergic receptors, and 30% (10 microM) for 5HT1A receptors. High affinity agonist binding for A1-, alpha 2-, and 5HT1A-receptors was virtually abolished by GTP gamma S in the presence of adenoregulin, but was only partially abolished in its absence. Magnesium ions increased the binding of agonists to receptors and reduced the enhancement elicited by adenoregulin. 3. The effect of adenoregulin on binding of N6-cyclohexyladenosine ([3H]CHA) to A1-receptors was relatively slow and was irreversible. Adenoregulin increased the Bmax value for [3H]CHA binding sites, and the proportion of high affinity states, and slowed the rate of [3H]CHA dissociation. Binding of the A1-selective antagonist, [3H]DPCPX, was maximally enhanced by only 13% at 2 microM adenoregulin. Basal and A1-adenosine receptor-stimulated binding of [35S]GTP gamma S were maximally enhanced 45% and 23%, respectively, by 50 microM adenoregulin. In CHAPS-solubilized membranes from rat cortex, the binding of both [3H]CHA and [3H]DPCPX were enhanced by adenoregulin. Binding of [3H]CHA to membranes from DDT1 MF-2 cells was maximally enhanced 17% at 20 microM adenoregulin. In intact DDT1 MF-2 cells, 20 microM adenoregulin did not potentiate the inhibition of cyclic AMP accumulation mediated via the adenosine A1 receptor. 4. It is proposed that adenoregulin enhances agonist binding through a mechanism involving enhancement of guanyl nucleotide exchange at G-proteins, resulting in a conversion of receptors into a high affinity state complexed with guanyl nucleotide-free G-protein.

Adenosine↗
PubMed1995

A new subclass of alkaloids from a dendrobatid poison frog: a structure for deoxypumiliotoxin 251H.

Deoxypumiliotoxin 251H [4], representing a new subclass of the pumiliotoxin-A class of alkaloids, has been isolated from a dendrobatid frog, Epipedobates tricolor. The structure, elucidated by nmr, gc-Ftir, and mass spectral analyses, is proposed to be an 8-methyl-6-(5-hydroxy-2-methylhexylidene)-1-azabicyclo[4.3.0]nonan e. The absolute stereochemistry and the relative configuration of the hydroxyl group are unknown.

Alkaloids↗
PubMed1995

Alkaloids from frog skins: selective probes for ion channels and nicotinic receptors.

Amphibian skin has provided a wide range of biologically active alkaloids, many of which have unique profiles of pharmacological activity and therapeutic potential. Over three hundred alkaloids have been identified and structures of over a dozen different classes of alkaloids have been elucidated. These include the batrachotoxins, which were shown to be potent and selective activators and ligands for sodium channels, the histrionicotoxins, which were shown to be potent non-competitive blockers and ligands for nicotine receptor channel complexes, the pumiliotoxins and related allo- and homo-pumiliotoxins, which were shown to have myotonic and cardiotonic activity due to effects on sodium channels, and epibatidine, which was shown to have potent antinociceptive activity due to selective agonist activity at nicotinic receptors. These alkaloids are known in nature only in amphibian skin, except for homobatrachotoxin, which was recently identified in feathers and skin of a bird. Further classes of alkaloids from amphibian skin include monocyclic pyrrolidines and piperidines, bicyclic decahydroquinolines, pyrrolizidines, indolizidines, and quinolizidines and tricyclic gephyrotoxins, pyrrolizidine oximes, pseudophrynamines, and coccinellines. These alkaloids also have activity in ion channels. It appears likely that all of the frog skin alkaloids are taken up and sequestered into the skin from the diet, which for such amphibians consists mainly of small arthropods. The pyrrolidines, piperidines, 3,5-disubstituted pyrrolizidines and 3,5-disubstituted indolizidines appear likely to be derived from ants, the coccinellines and related tricyclics from beetles and the pyrrolizidine oximes from millipedes. The origins of the batrachotoxins, histrionicotoxins, pumiliotoxins and epibatidine are of particular interest in view of their remarkable biological activities.

Alkaloids↗
PubMed1994

Chronic effects of ethanol on central adenosine function of mice.

Chronic ingestion of 5% ethanol had no significant effect on open field locomotor of NIH Swiss strain male mice, nor were the depressant effects of a non-selective adenosine receptor agonist, NECA, or the stimulant effects of a non-selective antagonist, caffeine significantly altered. The density of cerebral cortical A1-adenosine receptors and of nitrendipine binding sites on calcium channels were significantly increased after chronic ethanol, while the density of striatal A2a-adenosine receptors were unchanged. The locomotor stimulant effects of ethanol (2.5 g/kg) were slightly decreased after chronic ethanol, but were markedly reduced in mice after chronic caffeine ingestion. The results suggest some involvement of adenosine systems in the effects of ethanol.

Adenosine↗
PubMed1994

Functional characterization of the A2b adenosine receptor in NIH 3T3 fibroblasts.

The adenosine (ADO) receptor in NIH 3T3 fibroblasts was characterized using a series of adenosine agonists and selected xanthine and non-xanthine antagonists. The ADO receptor elicited accumulations of cyclic AMP in intact NIH 3T3 fibroblasts and caused activation of adenylate cyclase in membrane preparations. The receptor had characteristics of the A2b subtype of adenosine receptor. ADO analogs had relatively high EC50 values at the receptor and were antagonized competitively by xanthines. The rank order of potency for adenosine analogs in NIH 3T3 fibroblasts for cyclic AMP accumulation was: NECA > 2-ClADO > R-PIA >> CV1808, CGS 21680. The EC50 for 2-ClADO was 4.3 microM in intact cells and 15 microM in membrane preparations. All ADO analogs were more potent at the A2a receptor of pheochromocytoma PC12 membranes than at the A2b receptor of fibroblast NIH 3T3 membranes. Structure-activity relationships suggested that the regions of interaction with 5'- and N6-substituents of ADO were similar for both the PC12 A2a and NIH 3T3 A2b receptor. However, ADO analogs with large substituents in the 2'-position, such as 2-cyclohexylethoxy ADO and CGS 21680, were highly selective for the A2a receptor. All ADO analogs tested were stimulatory to adenylate cyclase at the NIH 3T3 A2b receptor, including 5'-methylthioADO, which was a weak partial agonist. A series of xanthine antagonists were not selective for the NIH 3T3 A2b versus the PC12 A2a receptor. In all cases, xanthines were more potent as antagonists in the intact NIH 3T3 cells than in NIH 3T3 membranes. In a series of non-xanthine antagonists, most compounds were equipotent or slightly more potent at the A2a receptor except for alloxazine, which was approximately 9-fold selective for the A2b receptor.

3T3 Cells↗
PubMed1994

Effects of ATP and UTP in pheochromocytoma PC12 cells: evidence for the presence of three P2 receptors, only one of which subserves stimulation of norepinephrine release.

1. In pheochromocytoma PC12 cells ATP and, to a lesser extent, 2-methylthioATP stimulate phosphoinositide breakdown, release of intracellular calcium, and influx of external calcium, leading to stimulation of norepinephrine release. In contrast, although UTP also stimulates phosphoinositide breakdown, release of intracellular calcium, and influx of external calcium, there is no stimulation of norepinephrine release. 2. 2-MethylthioATP, presumably acting at P2y receptors, and UTP, presumably acting at P2u receptors, in combination elicit a phosphoinositide breakdown greater than that elicited by either alone. Intracellular levels of calcium measured with Fura-2 increase to greater levels with ATP than with UTP and are sustained, while the UTP intracellular levels of calcium rapidly return to basal values. Both ATP and UTP cause a similar influx of 45 Ca2+ presumably by stimulation of a P2 receptor directly linked to a cation channel. 3. It is proposed that PC12 cells contain two distinct G protein-coupled P2 receptors that activate phospholipase C and a P2 receptor linked to a cation channel. The P2y receptor sensitive to ATP (and to 2-methylthioATP) causes the depletion of a pool of intracellular calcium, sufficient to activate so-called "receptor-operated calcium entry". The sustained elevation of intracellular calcium after ATP treatment is proposed to result in stimulation of norepinephrine release and activation of calcium-dependent potassium channels and sodium-calcium exchange pathways. 4. The P2u receptor sensitive to UTP (and to ATP) causes only a transient elevation in levels of intracellular calcium, perhaps from a different pool, insufficient to activate so-called receptor-operated calcium entry. Further sequelae do not ensue, and the functional role of the UTP-sensitive P2u receptor is unknown.

Adenosine Triphosphate↗
PubMed1994

Effects of the amphiphilic peptides mastoparan and adenoregulin on receptor binding, G proteins, phosphoinositide breakdown, cyclic AMP generation, and calcium influx.

1. The amphiphilic peptide mastoparan is known to affect phosphoinositide breakdown, calcium influx, and exocytosis of hormones and neurotransmitters and to stimulate the GTPase activity of guanine nucleotide-binding regulatory proteins. Another amphiphilic peptide, adenoregulin was recently identified based on stimulation of agonist binding to A1-adenosine receptors. 2. A comparison of the effects of mastoparan and adenoregulin reveals that these peptides share many properties. Both stimulate binding of agonists to receptors and binding of GTP gamma S to G proteins in brain membranes. The enhanced guanyl nucleotide exchange may be responsible for the complete conversion of receptors to a high-affinity state, complexed with guanyl nucleotide-free G proteins. 3. Both peptides increase phosphoinositide breakdown in NIH 3T3 fibroblasts. Pertussis toxin partially inhibits the phosphoinositide breakdown elicited by mastoparan but has no effect on the response to adenoregulin. N-Ethylmaleimide inhibits the response to both peptides. 4. In permeabilized 3T3 cells, both adenoregulin and mastoparan inhibit GTP gamma S-stimulated phosphoinositide breakdown. Mastoparan slightly increases basal cyclic AMP levels in cultured cells, followed at higher concentrations by an inhibition, while adenoregulin has minimal effects. 5. Both peptides increase calcium influx in cultured cells and release of norepinephrine in pheochromocytoma PC12 cells. The calcium influx elicited by the peptides in 3T3 cells is not markedly altered by N-ethylmaleimide. 6. Multiple sites of action appear likely to underlie the effects of mastoparan/adenoregulin on receptors, G proteins, phospholipase C, and calcium.

3T3 Cells↗
PubMed1994

Inhibition of platelet aggregation by adenosine receptor agonists.

2-(Ar)alkoxyadenosines, which are agonists selective for the A2AAR in PC 12 cell and rat striatum membranes, are also agonists at the A2AR coupled to adenylate cyclase (AC) that mediates the inhibition of platelet aggregation. A panel of twelve well-characterized adenosine analogues stimulated human platelet AC and inhibited ADP-induced platelet aggregation at sub- to low-micromolar concentrations with a potency ranking CGS 21680 > adenosine > R-PIA. There were significant correlations between the EC50 of anti-aggregatory activity and either the EC50 of stimulation of platelet and PC 12 cell AC (r2 = 0.66 and 0.67, respectively) or the Ki of inhibition of [3H]NECA binding to the rat striatum membranes (r2 = 0.75). Likewise, platelet AC stimulation correlated well with stimulation of PC 12 cell AC and with [3H]NECA binding (r2 = 0.94 and 0.91, respectively). Ten 2-(ar)alkoxyadenosines stimulated platelet AC at EC50s ranging between 0.16 and 2.3 microM and inhibited platelet aggregation at EC50s ranging between 2 and 30 microM. There were no correlations between the EC50s of anti-aggregatory activity and either the EC50s of the stimulation of platelet or PC 12 AC (r2 = 0.08 and 0.06, respectively) or with the Ki of the inhibition of [3H]NECA binding to the A2aAR in rat striatum (r2 = 0.02). The EC50s of the stimulation of platelet AC correlated with those of the stimulation of PC 12 AC (r2 = 0.48), and also with the Ki of [3H]NECA binding (r2 = 0.71). Each of the 23 adenosines completely inhibited platelet aggregation and thus, functionally, all behaved as full agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1994

First occurrence of tetrodotoxin in a dendrobatid frog (Colostethus inguinalis), with further reports for the bufonid genus Atelopus.

The water-soluble toxin present in skin of Colostethus inguinalis (Dendrobatidae) was identified as tetrodotoxin by fluorometric HPLC analysis. The amount of tetrodotoxin per frog skin was estimated by HPLC, mouse toxicity, and inhibition of [3H]saxitoxin binding to brain membranes as 0.1 to 1.2 micrograms. Small amounts of anhydrotetrodotoxin and 4-epietrodotoxin also were present. Tetrodotoxin-like activity was not detected by inhibition of [3H]saxitoxin binding in other species of Colostethus nor in other dendrobatids (Aromobates, Dendrobates, Phyllobates). Tetrodotoxin-like activity was present in extracts of skin of five species of Atelopus (Bufonidae). HPLC analysis identified tetrodotoxin as the major toxic component in Atelopus spumarius and A. varius, as a minor component in A. spurrelli, and as a trace component in A. ignescens and A. zeteki. The major tetrodotoxin-like compounds in the last three species were not identified. Tetrodotoxin-like activity was not detected by inhibition of [3H]saxitoxin binding in skin extracts from three other genera of bufonids.

Amphibian Venoms↗
PubMed1994

An uptake system for dietary alkaloids in poison frogs (Dendrobatidae).

The skin of poison frogs (Dendrobatidae) contains a wide variety of alkaloids that presumably serve a defensive role. These alkaloids persist for years in captivity, but are not present in captive-raised frogs. Alkaloids fed to poison frogs (Dendrobates, Phyllobates, Epipedobates) are readily accumulated into skin, where they remain for months. The process can be selective; an ant indolizidine is accumulated, while an ant pyrrolidine is not. Frogs (Colostethus) of the same family, which do not normally contain alkaloids, do not accumulate alkaloids. Such an alkaloid uptake system provides a means of maintaining skin alkaloids and suggests that some if not all such 'dendrobatid alkaloids' may have a dietary origin.

Alkaloids↗
PubMed1994

Epibatidine, a potent analgetic and nicotinic agonist.

Synthetic (+)- and (-)-epibatidine (an alkaloid originally characterized from frog skin) have potent analgetic activity in mice, using the hot-plate assay. The natural (+)-enantiomer, with an ED50 of about 1.5 micrograms/kg upon intraperitoneal injection, is about 2-fold more potent than the (-)-enantiomer. The analgetic activity is blocked by the nicotinic antagonist mecamylamine. Both the (+)- and (-)-enantiomers have high affinity (Ki values of 0.045 and 0.058 nm, respectively) for nicotinic sites that bind [3H] nicotine in rat brain membranes. An analog of epibatidine with the chloro substituent of the pyridyl ring replaced with hydrogen has comparable affinity for nicotinic sites, whereas replacement with a methyl or iodo substituent lowers activity. Both (+)- and (-)-epibatidine have potent agonist activity at ganglionic-type nicotinic receptors in pheochromocytoma PC-12 cells, with EC50 values for stimulation of sodium influx of 72 and 111 nM, respectively. (-)-Epibatidine is about 5-fold less potent as an agonist at muscle-type central nicotinic receptors of medulloblastoma TE671 cells. It would appear that the analgetic activity of epibatidine is due to activity as a nicotinic agonist. The epibatidines have little or no activity at a variety of other central receptors, including opioid receptors, muscarinic receptors, adrenergic receptors, dopamine receptors, serotonin receptors, and gamma-aminobutyric acid receptors.

Analgesics↗
PubMed1993

A role for central A3-adenosine receptors. Mediation of behavioral depressant effects.

The behavioral effects of a selective A3 adenosine receptor agonist 3-IB-MECA (N6-(3-iodobenzyl)-5'-N-methylcarboxamidoadenosine) in mice and the localization of radioligand binding sites in mouse brain were examined. Low levels of A3 adenosine receptors were detected in various regions of the mouse brain (hippocampus, cortex, cerebellum, striatum), using a radioiodinated, high-affinity A3-agonist radioligand [125I]AB-MECA (N6-(3-iodo-4-aminobenzyl)-5'-N-methylcarboxamidoadenosine). Scatchard analysis in the cerebellum showed that the Kd value for binding to A3 receptors was 1.39 +/- 0.04 nM with a Bmax of 14.8 +/- 2.1 fmol/mg protein. 3-IB-MECA at 0.1 mg/kg i.p. was a locomotor depressant with > 50% reduction in activity. Although selective A1 or A2a antagonists reversed locomotor depression elicited by selective A1 or A2a agonists, respectively, the behavioral depressant effects of 3-IB-MECA were unaffected. 3-IB-MECA also caused scratching in mice, which was prevented by coadministration of the histamine antagonist cyproheptadine. The demonstration of a marked behavioral effect of A3 receptor activation suggests that the A3 receptor represents a potential new therapeutic target.

Adenosine↗
PubMed1993

Syntheses of 2,5- and 2,6-difluoronorepinephrine, 2,5-difluoroepinephrine, and 2,6-difluorophenylephrine: effect of disubstitution with fluorine on adrenergic activity.

Synthetic routes to difluorinated analogs of the adrenergic agonists, norepinephrine (NE), epinephrine (E), and phenylephrine (PE) have been developed. The syntheses were based on elaboration of the ethanolamine side chains from the appropriately polyfunctionalized benzaldehydes. The benzaldehydes were prepared from precursor difluorinated benzenes by sequential regioselective lithiations and reaction with electrophiles to introduce hydroxyl and carboxaldehyde functionalities. Binding and functional assay data demonstrate that the 2,6-difluorinated analogs are relatively inactive at both alpha- and beta-adrenergic receptors. These results are consistent with earlier observations that 2-fluoro substitution of adrenergic agonists decreases alpha-adrenergic activity whereas 6-fluoro substitution decreases beta-adrenergic activity.

Animals↗
PubMed1993

Stimulation of calcium release by caffeine analogs in pheochromocytoma cells.

Caffeine (EC50 approximately 20 mM) causes a maximal 400% increase in intracellular calcium ion concentration ([Ca2+]i) in pheochromocytoma PC12 cells. A range of caffeine analogs in which methyl groups at the 1, 3, and 7 positions were replaced with relatively nonpolar (ethyl, allyl, propyl, propargyl) or polar (CH2COOH, CH2CH2OH, CH2CN, CH2OCH3) substituents were tested at a 10 mM concentration. Many analogs were as efficacious or only somewhat less efficacious than 10 mM caffeine. Certain analogs with polar substituents had no effect. Disubstituted xanthines were less efficacious (theophylline, paraxanthine) than caffeine or were ineffective (theobromine). 1-Propyl-3,7-dimethylxanthine (EC50 4 mM) and 1-propargyl-3,7-dimethylxanthine (EC50 5 mM) were several-fold more potent than caffeine in causing elevation of [Ca2+]i and the latter was at least as efficacious.

Animals↗