Biomedical subjects

J W Daly

Publications and source records attributed to J W Daly.

At least 73 records · Page 4Linked to original sources

PubMed1993

Synthesis of paraxanthine analogs (1,7-disubstituted xanthines) and other xanthines unsubstituted at the 3-position: structure-activity relationships at adenosine receptors.

Synthetic procedures for the preparation of various 3-unsubstituted xanthines, including paraxanthine analogs (1,7-disubstituted xanthines) and 1,8-disubstituted xanthines, were developed. Silylation of 1-substituted xanthines followed by alkylation at the 7-position provides a facile route to paraxanthine analogs. Regioselective alkylation of tris(trimethylsilyl)-6-aminouracil provides 3-substituted 6-aminouracils, which are converted to 1,8-disubstituted xanthines by standard procedures. The ring closure of 3-substituted 5-cyclopentanecarboxamido- and 5-(benzoylamino)-6-aminouracils requires drastic reaction conditions. Affinity for brain A1 and A2 adenosine receptors was determined in binding assays for these and other xanthines with substituents in 1-, 3-, 7-, 8-, and 9-positions. Substitution at the 1-position was necessary for high affinity at adenosine receptors. 1,3-Disubstituted xanthines generally had higher affinity than 1,7-disubstituted xanthines. 1,8-Disubstituted xanthines had high affinity for adenosine receptors; some were highly selective for A1 receptors.

Animals↗

PubMed1993

Effect of trifluoromethyl and other substituents on activity of xanthines at adenosine receptors.

An aryl p-(trifluoromethyl) substituent increases the affinity of 1,3-disubstituted 8-phenylxanthines at A2a-adenosine receptors, while having little effect on affinity at A1-adenosine receptors. In contrast, an aryl p-(trifluoromethyl) substituent has little effect on affinity of 3,7-disubstituted and 1,3,7-trisubstituted 8-phenylxanthines. An aryl p-sulfo substituent reduces affinity of all 8-phenylxanthines at A1- and A2a-adenosine receptors. An 8-(trifluoromethyl) substituent markedly reduces affinity of 1,3-dialkylxanthines at both A1- and A2a-adenosine receptors. In contrast, 8-(trifluoromethyl)caffeine retains affinity for A2a-adenosine receptors, but does lose affinity for A1-adenosine receptors. 8-Bromo-, 8-acryl-, and 8-pent-1-enylcaffeines are also selective for A2-adenosine receptors, while 8-cyclobutylcaffeine is nonselective. 8-[trans-2-(tert-butyloxycarbonyl)vinylcaffeine is 20-fold selective for Aza vs A1 receptors.

Acylation↗

PubMed1993

8-(3-Chlorostyryl)caffeine (CSC) is a selective A2-adenosine antagonist in vitro and in vivo.

An adenosine antagonist, 8-(3-chlorostyryl)caffeine (CSC), was shown previously to be 520-fold selective for A2a-adenosine receptors in radioligand binding assays in the rat brain. In reversing agonist effects on adenylate cyclase, CSC was 22-fold selective for A2a receptors in rat phenochromocytoma cells (Kb 60 nM) vs. A1 receptors in rat adipocytes (Kb 1.3 microM). Administered i.p. in NIH mice at a dose of 1 mg/kg, CSC shifted the curve for locomotor depression elicited by the A2a-selective agonist APEC to the right (ED50 value for APEC shifted from 20 micrograms/kg i.p. to 190 micrograms/kg). CSC had no effect on locomotor depression elicited by an ED50 dose of the A1-selective agonist CHA. CSC alone at a dose of 5 mg/kg stimulated locomotor activity by 22% over control values. Coadministration of CSC and the A1-selective antagonist CPX, both at non-stimulatory doses, increased activity by 37% (P < 0.001) over CSC alone, suggesting a behavioral synergism of A1- and A2-antagonist effects in the CNS.

Adenosine↗

PubMed1993

Chronic caffeine alters the density of adenosine, adrenergic, cholinergic, GABA, and serotonin receptors and calcium channels in mouse brain.

1. Chronic ingestion of caffeine by male NIH strain mice alters the density of a variety of central receptors. 2. The density of cortical A1 adenosine receptors is increased by 20%, while the density of striatal A2A adenosine receptors is unaltered. 3. The densities of cortical beta 1 and cerebellar beta 2 adrenergic receptors are reduced by ca. 25%, while the densities of cortical alpha 1 and alpha 2 adrenergic receptors are not significantly altered. Densities of striatal D1 and D2 dopaminergic receptors are unaltered. The densities of cortical 5 HT1 and 5 HT2 serotonergic receptors are increased by 26-30%. Densities of cortical muscarinic and nicotinic receptors are increased by 40-50%. The density of cortical benzodiazepine-binding sites associated with GABAA receptors is increased by 65%, and the affinity appears slightly decreased. The density of cortical MK-801 sites associated with NMDA-glutaminergic receptors appear unaltered. 4. The density of cortical nitrendipine-binding sites associated with calcium channels is increased by 18%. 5. The results indicate that chronic ingestion of caffeine equivalent to about 100 mg/kg/day in mice causes a wide range of biochemical alterations in the central nervous system.

Animals↗

PubMed1993

Locomotor activity in mice during chronic treatment with caffeine and withdrawal.

Chronic ingestion of caffeine by mice caused a marked reduction in locomotor exploratory activity. At least 4 days of withdrawal were required to restore activity to normal levels. Stimulatory effects of injected caffeine were lower in chronically treated mice and the biphasic dose-response (stimulatory followed by depressant) curve for injected caffeine was left shifted. Seven days of withdrawal were required before the dose-response curve to caffeine was identical to that of control mice. The depressant effects of a potent xanthine phosphodiesterase inhibitor, 1,3-dipropyl-7-methylxanthine, were blunted in caffeine-treated mice. The depressant effects of A1- and A2-selective adenosine analogs were enhanced after chronic caffeine. There was little or no effect of chronic caffeine on the stimulatory effects of dopaminergic agents (amphetamine, caffeine), while both depressant and stimulatory effects of cholinergic agents (nicotine, oxotremorine, scopolamine) were reduced. The results indicate that chronic caffeine affects functions of adenosine and cholinergic receptors related to regulation of locomotor exploratory activity.

1-Methyl-3-isobutylxanthine↗

PubMed1993

Alkaloids from bufonid toads (Melanophryniscus): decahydroquinolines, pumiliotoxins and homopumiliotoxins, indolizidines, pyrrolizidines, and quinolizidines.

Skins of bufonid toads of the genus Melanophryniscus contain several classes of alkaloids: decahydroquinolines, pumiliotoxins, allopumiliotoxins, homopumiliotoxins, both 3,5- and 5,8-disubstituted indolizidines, 3,5-disubstituted pyrrolizidines, and a 1,4-disubstituted quinolizidine. Tricyclic alkaloids, including precoccinelline [193A] and alkaloid 236, an oxime methyl ether, are present in one population of Melanophryniscus stelzneri.

Alkaloids↗

PubMed1993

Alkaloids in Madagascan frogs (Mantella): pumiliotoxins, indolizidines, quinolizidines, and pyrrolizidines.

Brightly colored ranid frogs of the genus Mantella are found only in rain forests of Madagascar. Gc-ms and gc-Ft-ir analyses of skin alkaloids of seven different species, including four populations of Mantella madagascariensis, are reported. All contain one or more representatives of the pumiliotoxin A (PTX-A) class with the 13,14-dihydro derivatives 309A and 325A found in major amounts in the four populations of M. madagascariensis, while 307A (PTX-A) is found in two populations of M. madagascariensis and in three additional species, Mantella aurantiaca, Mantella viridis, and Mantella crocea. The latter three species also contain appreciable quantities of 323A (PTX-B). The four populations of M. madagascariensis show major amounts of two 1,4-disubstituted quinolizidines, 217A and 231A, and a 5,8-disubstituted indolizidine, 217B, in addition to many minor or trace quinolizidines and indolizidines. Such disubstituted quinolizidines and indolizidines are present as trace alkaloids in the six other species of Mantella, along with 3,5-disubstituted indolizidines, 3,5-disubstituted pyrrolizidines, the decahydroquinoline cis-195A, tricyclic alkaloids, and homopumiliotoxins. A new alkaloid class, which appears to contain a quinolizidine moiety, is seen in M. aurantiaca and M. crocea and is represented by 235C and several congeners.

Alkaloids↗

PubMed1993

Structure-activity relationships for 2-substituted adenosines at A1 and A2 adenosine receptors.

A series of 55 2-alkyloxy-, 2-aryloxy- and 2-aralkyloxy-adenosines was screened as inhibitors of the binding of [3H]R-phenyl-isopropyladenosine to A1 adenosine receptors in rat cerebral cortical membranes, and of the binding of [3]N-ethylcarboxamidoadenosine to A2 adenosine receptors in rat striatal membranes and as agonists at A2 adenosine receptors coupled to adenylate cyclase in rat pheochromocytoma PC12 cell membranes. The activities are consonant with a hydrophobic binding site in the A2 receptors at a distance from the 2-position of the adenine ring corresponding to a spacer chain of -O-CH2-CH2-. These is little lateral steric tolerance in the region occupied by the spacer chain. Interaction with the hydrophobic binding site is greatest in the 2-alkyloxy series for 2-cyclohexylethoxy-, 2-cyclohexylpropoxy- and 2-cyclohexylbutoxyadenosines and in the 2-aralkoxy series for 2-phenylethoxy-, 2-(4-methylphenyl)ethoxy-, 2-(4-chlorophenyl)ethoxy-, and 2-naphthylethoxy-adenosine. The affinities of the 2-substituted adenosines for the rat cerebral cortical A1 receptors are not as markedly altered by structural changes and are in almost all cases two- to hundredfold less than the affinity of the 2-substituted adenosine for the rat striatal A2 receptor. There is excellent correspondence of the present data on rat A2 receptors with reported potencies of these 2-substituted adenosines as coronary vasodilators in guinea pig heart preparations.

Adenosine↗

PubMed1992

Frog secretions and hunting magic in the upper Amazon: identification of a peptide that interacts with an adenosine receptor.

A frog used for "hunting magic" by several groups of Panoan-speaking Indians in the borderline between Brazil and Peru is identified as Phyllomedusa bicolor. This frog's skin secretion, which the Indians introduce into the body through fresh burns, is rich in peptides. These include vasoactive peptides, opioid peptides, and a peptide that we have named adenoregulin, with the sequence GLWSKIKEVGKEAAKAAAKAAGKAALGAVSEAV as determined from mass spectrometry and Edman degradation. The natural peptide may contain a D amino acid residue, since it is not identical in chromatographic properties to the synthetic peptide. Adenoregulin enhances binding of agonists to A1 adenosine receptors; it is accompanied in the skin secretion by peptides that inhibit binding. The vasoactive peptide sauvagine, the opioid peptides, and adenoregulin and related peptides affect behavior in mice and presumably contribute to the behavioral sequelae observed in humans.

Amino Acid Sequence↗

PubMed1992

Homobatrachotoxin in the genus Pitohui: chemical defense in birds?

Three passerine species in the genus Pitohui, endemic to the New Guinea subregion, contain the steroidal alkaloid homobatrachotoxin, apparently as a chemical defense. Toxin concentrations varied among species but were always highest in the skin and feathers. Homobatrachotoxin is a member of a class of compounds collectively called batrachotoxins that were previously considered to be restricted to neotropical poison-dart frogs of the genus Phyllobates. The occurrence of homobatrachotoxin in pitohuis suggests that birds and frogs independently evolved this class of alkaloids.

Animals↗

PubMed1992

Selective stimulation of Ca2+ flux in cells by maitotoxin.

Maitotoxin elicits a dose-dependent stimulation of 45Ca2+ influx in glioma C6, pheochromocytoma PC12, insulinoma HIT and human blood cells, while having no effect in liposomes. In HIT cells maitotoxin also elicited influx of 86Rb+ greater than 22Na+ greater than 54Mn2+, but the stimulation was far less than for 45Ca2+. Stimulation of 45Ca2+ influx was blocked by Ni2+, Co2+, Cd2+ and Mn2+, and markedly reduced by Ba2+. Divalent cations, in particular Ca2+, Ba2+, Mn2+ and Cd2+, enhanced influx of the monovalent cations 22Na+ and 86Rb+.

Animals↗

PubMed1992

Molecular species analysis of a product of phospholipase D activation. Phosphatidylethanol is formed from phosphatidylcholine in phorbol ester- and bradykinin-stimulated PC12 cells.

Tumor-promoting phorbol esters or calcium-mobilizing receptor ligands stimulate phosphatidylcholine breakdown and in many cells this is accompanied by phospholipase D (PLD) activation. We tested whether or not a direct relationship exists between these two phenomena. Pheochromocytoma (PC12) cells were stimulated with the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate or with the calcium-mobilizing receptor ligand bradykinin in media containing 1% ethanol. The fatty acid composition of the molecular species of phosphatidylethanol (PEt), a product of PLD activation, formed in stimulated cells was compared with the molecular species of endogenous phospholipids isolated from unstimulated PC12 cells. PEt was isolated and analyzed by fast atom bombardment-mass spectrometry (FAB-MS) in the negative ion mode. Fatty acid composition and headgroup structure of the major PEt molecular ions were confirmed by linked scan analysis. Phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol were isolated from unstimulated cells and converted into phosphatidic acids using PLD. Mass spectra of the respective phosphatidic acids were obtained by fast atom bombardment-mass spectrometry as described above. The molecular species of PEt formed in 12-O-tetradecanoylphorbol-13-acetate- and bradykinin-stimulated PC12 cell were identical to those of phosphatidylcholine isolated from untreated cells.

Animals↗

PubMed1992

Bis(monoacylglycero)phosphate from PC12 cells, a phospholipid that can comigrate with phosphatidic acid: molecular species analysis by fast atom bombardment mass spectrometry.

Phospholipids from pheochromocytoma (PC12) cells were purified by one-dimensional thin-layer chromatography (TLC). Material corresponding in RF to phosphatidic acid (PA) was analyzed by fast atom bombardment mass spectrometry (FAB). The molecular ions of the major constituents corresponded in mass to phosphatidylglycerols (PG), which, however, have a lower RF value. Analysis of the mass spectra demonstrated that this material consists of bis(monoacylglycero)phosphates (BMP, lysobisphosphatidic acid), a structural isomers of PG. Linked scans of individual molecular ions indicate that BMP from PC12 cells is esterified almost exclusively with monounsaturated (16:1 and 18:1) and polyunsaturated (20:4 and 22:6) fatty acids. One of the two major molecular species contains two monounsaturated (18:1/18:1), while the other contains both a monounsaturated (18:1) and a polyunsaturated (22:6) fatty acid ester. FAB in combination with TLC is ideally suited for analysis of molecular species of phospholipids.

Animals↗

PubMed1992

Agonist activity of 2- and 5'-substituted adenosine analogs and their N6-cycloalkyl derivatives at A1- and A2-adenosine receptors coupled to adenylate cyclase.

The activity of N6-cycloalkyl derivatives of adenosine, 2-chloroadenosine, 5'-chloroadenosine and N-ethylcarboximidoadenosine (NECA) and of 2-fluoroadenosine and 5-methylthioadenosines were compared at the A1-adenosine receptor inhibitory to adenylate cyclase in rat fat cell membranes and at the A2A-adenosine receptors stimulatory to adenylate cyclase in rat PC12 cell membranes. The N6-cycloalkyl derivatives in all cases were more potent (4- to 23-fold) than the parent compound at the A1 receptor, and were less potent (1.6- to 11-fold) than the parent compound at the A2A receptor. N6-Cyclopentyl-5'-chloroadenosine was the most selective agonist (900-fold) for the A1 receptor, while 2-fluoroadenosine was the only agonist with some selectivity (4.8-fold) for the A2A receptor. 5'-Methylthioadenosine was a weak agonist at both adenosine receptors. A 2-fluoro derivative of 5'-methylthioadenosine was somewhat more potent. Affinities of these analogs for inhibition of binding of radioligands to rat brain A1 and A2A receptors are presented.

Adenosine↗

PubMed1992

Variability in alkaloid profiles in neotropical poison frogs (Dendrobatidae): genetic versus environmental determinants.

Dendrobatid frogs produce a diverse set of alkaloids, whose profiles appear characteristic of frogs of each species or, in the case of variable species, of each population. In the case of one widespread species, Dendrobates auratus, alkaloid profiles in extracts of skin are markedly different in three populations, one from a Pacific island, Isla Taboga, Panama, one from central mountains in Panama, and the third from the Caribbean coast in Costa Rica. The first contains three major classes of dendrobatid alkaloids, the histrionicotoxins, the pumiliotoxin-A class and the decahydroquinolines. The second contains mainly histrionicotoxins, pumiliotoxin-A class alkaloids and one indolizidine. The third contains histrionicotoxins, a homopumiliotoxin, one decahydroquinoline, and a variety of indolizidines, quinolizidines and pyrrolizidines. Frogs from Isla Taboga or a nearby island were introduced into the Manoa Valley, Oahu, Hawaii, in 1932. Remarkably, although alkaloids of the pumiliotoxin-A class and one decahydroquinoline are still major constituents in skin extracts of Hawaiian frogs descended from the 1932 founding population, histrionicotoxins are absent and a novel tricyclic alkaloid is present. Offspring of wild-caught parents from Hawaii, Panama or Costa Rica raised in indoor terrariums on a diet of crickets and fruit flies do not contain detectable amounts of skin alkaloids. Offspring raised in large outside terrariums in Hawaii and fed mainly wild-caught termites and fruit flies do contain the same profile of alkaloids as their wild-caught parents in Hawaii, but at reduced levels. The genetic, environmental and dietary determinants of alkaloid profiles in dendrobatid frogs remain obscure, in particular the underlying cause for total absence in terrarium-reared frogs.

Alkaloids↗

PubMed1992

A new class of alkaloids from a dendrobatid poison frog: a structure for alkaloid 251F.

Alkaloids of a new class are present in skin extracts of the dendrobatid poison frog, Minyobates bombetes, of Colombia. The structure of the major alkaloid of this class, 251F, has been determined as a trimethylcyclopenta[b]quinolizidinemethanol 1 by nmr, gc-Ft-ir, and ms studies including ms-ms. At least nine congeners of 251F were detected in these extracts.

Alkaloids↗

PubMed1992

Effects of the amphiphilic peptides melittin and mastoparan on calcium influx, phosphoinositide breakdown and arachidonic acid release in rat pheochromocytoma PC12 cells.

Two amphiphilic peptides from hymenopterid insects, melittin and mastoparan, stimulate secretion in a variety of cell types. In PC12 cells, both peptides stimulate calcium influx with melittin some 20-fold more potently than mastoparan. Melittin stimulates both breakdown of phosphoinositides (Pl) by phospholipase C to yield inositol phosphates and hydrolysis of phospholipids by phospholipase A2 to release arachidonic acid (AA). Mastoparan stimulates Pl breakdown, but has no effect on AA release. Maximal stimulation of Pl breakdown occurs at 1 to 2.5 micrograms/ml melittin and 30 micrograms/ml mastoparan, whereas maximal stimulation of AA release occurs at 2 to 5 micrograms/ml melittin. Organic calcium channel blockers (nifedipine, verapamil, diltiazem) have little or no effect on responses to the peptides. The influx of calcium elicited by melittin or mastoparan is completely or nearly completely blocked by inorganic calcium channel blockers (Co++, Mn++, Cd++). Mn++ and Cd++ inhibit melittin-induced Pl breakdown and AA release and mastoparan-induced Pl breakdown. Co++ has no effect on melittin-induced Pl breakdown and potentiates mastoparan-induced Pl breakdown. Pertussis toxin has no effect on the Pl breakdown induced by either peptide. The responses to melittin and mastoparan in PC12 cells are compared to those reported for maitotoxin.

Animals↗

PubMed1992

A2A adenosine receptors from rat striatum and rat pheochromocytoma PC12 cells: characterization with radioligand binding and by activation of adenylate cyclase.

Binding assays and assays of activation of adenylate cyclase with the agonists 5'-N-ethylcarboxyamidoadenosine (NECA) and CGS21680 have been used to compare adenosine receptors in rat pheochromocytoma PC12 cells and in rat striatum. The [3H]NECA binding showed two components, whereas [3H]CGS21680 bound to one component in both tissues. The Kd value for the high affinity site labeled with [3H]NECA in PC12 cell membranes (2.3 nM) was lower than that in striatum (6.5 nM). The [3H]CGS21680 binding site showed a Kd value of 6.7 nM and 11.3 nM in PC12 cells and striatum, respectively. In the presence of GTP the KD values of [3H]NECA and [3H]CGS21680 for the high affinity site were increased severalfold, whereas the low affinity sites for [3H]NECA were no longer detected with filtration assays. A comparison of the ability of a series of agonists and antagonists to inhibit high affinity binding of [3H]NECA to A2 receptors in PC12 cell and striatal membranes indicated that agonists had higher affinities and antagonists had lower affinities in PC12 cells, compared with affinities in striatal membranes. Analysis of activation of adenylate cyclase in PC12 cell membranes suggested that the dose-dependent stimulation by NECA involved two components, whereas CGS21680 stimulated via one component. The maximal stimulation by NECA significantly exceeded that caused by CGS21680. In intact PC12 cells, NECA caused a greater accumulation of AMP than did CGS21680, as was the case in membranes. In striatal membranes, NECA and CGS21680 showed similar maximal stimulations of adenylate cyclase. Both NECA and CGS21680 were more potent in PC12 cell membranes than in striatal membranes, in agreement with binding data. However, in contrast to binding data, antagonists were not less potent versus stimulation of adenylate cyclase by NECA or CGS21680 in PC12 cell membranes, compared with striatal membranes. In toto, the results suggest that A2A receptors in striatum are virtually identical to the A2A receptors in PC12 cells. But, in addition to an A2A receptor, it appears that a lower affinity functional receptor, probably an A2B receptor, is present in PC12 cells and PC12 cell membranes, whereas such a functional low affinity receptor is not detectable in striatal membrane.

Adenosine↗