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The antitussive drug pholcodine does not bind to mu or delta opioid receptors
EVIDENCE OF CORRELATIONS BETWEEN MORPHINE ANALGESIA AND H3-HISTAMINE RECEPTORS. R . A r r i g o - R e i n a , S.Chiechio, C.Spadaro. Institute of Pharmacology and Pharmacognosy Viale A . D o r i a , 6 , 95125 Catania, Italy.
THE ANTITUSSIVE DRUG PHOLCODINE MU O R DELTA O P I O I D R E C E P T O R S
D O E S NOT BIND TO
M. Attila, J. Walden and J. Aaltonen1 Division of Pharmacology and Toxicology, Department of Pharmacy, University of Helsinki and ILeiras Oy, Helsinki, Finland.
Evidence indicate the presence of presynaptic H3-recej~ tot-mediating inhibition of neural histamine release in various CNS regions. Since we previously ascertained that inhibition of neural histamine synthesis by FMH or chronic depletion of mast-cell histamine by 48/80 enhanced latency and increased morphine analgesia on the T a i l - F l i c k test in rats(1,2), this study was u n d e r t a k en to evaluate the role played by H3-receptors on the histaminevgic mechanisms mediating pain sensitivity and also, on the antinociceptive action of morphine in rats. R-~-Methylhistamine, a selective H3-agonist, and Thiop_e ramide, a selective H3-antagonist, were injected at doses of 1-2 m g / k g , s c . , a n d 10-15 m g / k g , i p . , r e s p e c t i v e l y . MorphineHCI was injected at doses of 5-10 mg/kg,sc. Analgesia was recorded by the T a i l - F l i c k test and ex pressed as %MPE. Data were analyzed by ANOVA. Results showed that R-(]-Methylhistamine decreased tail -latency, whereas Thioperamide did no. The H3-antago nist, injected 15 rain before, reduced the hyperalgesic effect of the H3-agonist, also increasing morphine anal gesia. Data of this study hypothesize that H3=histamine receptors may regulate the release of other neurotran_s mitters, thus confirming that H3-receptors may not be confined to histamine-containing neurones in the CNS. 1) R . A r r i g o - R e i n a et al.,Pharmac. Res.20,243,1988. 2} R . A r r i g o - R e i n a , Agents and Actions,30,210,1990.
Pholcodine is used as an antitussive agent. Although structurally related to morphine pholcodine does not have analgesic properties. The classification of pholcodine into narcotic drugs, however, restricts its marketing inside the European Union. Binding of pholcodine to opioid receptors has been only sporadically studied. Chert et al. (Life Sci. 48: 2165-2171, 1991) reported negligible binding of pholcodine to tJ opioid receptors (about 4700 times lower affinity than morphine). In this study we have confirmed the low affinity of pholcodine to p opioid receptors and report its even lower affinity to 8 opioid receptors. Synaptosomes (P2 fraction) prepared from whole brain (minus cerebellum) of adult male Wistar rats (Lazarus et al., J. Med. Chem. 35: 1222-1227, 1992) were used for the binding assays. Competition studies with pholcodine, morphine, DAMGO or DPDPE were conducted using 6 nM [aH]DPDPE and 3.5 nM [3H]DAMGO to label 6 and p sites, respectively. The non-specific binding was defined by displacing the label with 1.95 or 1.55 pM DPDPE or DAMGO, respectively. Competition curves were calculated by using non-linear regression analysis each combined from 3 to 5 assays using different synaptosome preparations. In this study we found that the pholcodine was about 1400 and 900 times less potent on opioid p and 8 receptors, respectively, than morphine. K opioid receptor binding studies ([3H]U69593 as ligand) are in progress. In conclusion, the antitussive effect of pholcodine cannot be related to p or 8 opioid receptors.
This work was supported by a Grant of MURST.
MONOCYCLIC COMPOUNDS STRUCTURALLY RELATED TO THE ~t-OPIOID AGONIST 3,8DIAZABICYCLO[3.2.1]OCTANES D. Barloceo1, G. Cignarella2, S. Villa2, L. Toma 3, W. Fratta4, P. Fadda4 1) Dip. Scienze Farmaceutiche, Universita' di Modena (Italy); 2) Ist. Chim. Farm. e Toss., Universita' di Milano (Italy); 3) Dip. Chimiea Organica, Universita' di Pavia (Italy); 4) Dip. Neuroseienze, Universita' di Cagliari (Italy)
I N H I B I T I O N BY M O R P H I N E , BUT NOT BY GABA, O F DIMETHYLPHENYLPIPERAZINIUM-INDUCED EMESIS IN CATS DoBoBeleslin and S.K.Krstid Department of Pharmacology, Faculty of Medicine and Department of Pharmacology, Faculty of Pharmacy, P.O.Box 662, 11000 Belgrade, Yugoslavia
We have recently proposed (1) a possible pharmaeophore for a new class of p,-selective opioid agonists of general structure 1. Besides the well known elements shared by most opiates (namely an aromatic system placed at an appropriate distance from a tertiary amine function) this model suggests the existence of a small hydrophobie pocket able to accept the endoethylenic bridge of DBOs moiety. To verify the importance of this requisite, we designed several monoeyclic derivatives (2,4) structurally related to 1 but lacking the endoethylenie bridge. In this contribute the modeling of the compounds is reported together with their chemical synthesis and their affinity for ~t receptors. Molecular modeling of 2-4 was performed by molecular mechanics calculations and allowed to determine their preferred conformations. Moreover, high field t H-NMR spectroscopy was used to confirm the results of the modeling.
The central inhibitory mechanisms subserving the emesis are still ill understood. Therefore, the aim of the present experiments was to study the effect of morphine and GABA on dimethylphenylpiperazinium (DMpP)-induced emesis in cats. In an aseptic operation under pentobarbital sodium (35-40 mg/kg i.p.) anaesthesia an infusion cannula was implanted into the left lateral cerebral ventricles of cats of either sex (2-4 kg) so that intracerebroventricular (ioc.v.) injections of drugs could be made without anaesthesia. In a separate series of experiments, the area postrema was destroyed electrolyticaUy. Only expulsion of the gastric content, was taken as a positive emetic response° In the first series of experiments, DMPP (1.0 nag) injected i°c.v. induced emesis in 83 % of cats, and even with highest doses of 2 nag never reached 100%o In the second series of experiments, the effect of morphine (0.005-0.05 rag) and GABA (0.5-1.0 nag), injected ioC.V° 20 minutes before the emetic challenge inhibited the emesis induced by DMPP (1:0 nag) similarly injected. In the third series of experiments i°eoVo DMPP (1 o0 rag) failed to evoke emesis in cats with ablated area postremao It is apparent that opioids, rather than GABA, might be a putative inhibitory neurotransmitters within the area postrema of the cat.
iR(R')
I
R'(R) 1
?H3
?H3
~_CH2~:(3R,) ~N_~NR(R') ~¢NR(R', I
R'(R) 2
R = COCH2CH3
l
R'(R) 3
I
R'(R) 4
R' = CH2CH=CHC6H~
l) E. Novellino et al., J. Comput.-Aided Mol. Design, 5, 335, 1991
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116--
THE ANTITUSSIVE DRUG PHOLCODINE MU O R DELTA O P I O I D R E C E P T O R S
D O E S NOT BIND TO
M. Attila, J. Walden and J. Aaltonen1 Division of Pharmacology and Toxicology, Department of Pharmacy, University of Helsinki and ILeiras Oy, Helsinki, Finland.
Evidence indicate the presence of presynaptic H3-recej~ tot-mediating inhibition of neural histamine release in various CNS regions. Since we previously ascertained that inhibition of neural histamine synthesis by FMH or chronic depletion of mast-cell histamine by 48/80 enhanced latency and increased morphine analgesia on the T a i l - F l i c k test in rats(1,2), this study was u n d e r t a k en to evaluate the role played by H3-receptors on the histaminevgic mechanisms mediating pain sensitivity and also, on the antinociceptive action of morphine in rats. R-~-Methylhistamine, a selective H3-agonist, and Thiop_e ramide, a selective H3-antagonist, were injected at doses of 1-2 m g / k g , s c . , a n d 10-15 m g / k g , i p . , r e s p e c t i v e l y . MorphineHCI was injected at doses of 5-10 mg/kg,sc. Analgesia was recorded by the T a i l - F l i c k test and ex pressed as %MPE. Data were analyzed by ANOVA. Results showed that R-(]-Methylhistamine decreased tail -latency, whereas Thioperamide did no. The H3-antago nist, injected 15 rain before, reduced the hyperalgesic effect of the H3-agonist, also increasing morphine anal gesia. Data of this study hypothesize that H3=histamine receptors may regulate the release of other neurotran_s mitters, thus confirming that H3-receptors may not be confined to histamine-containing neurones in the CNS. 1) R . A r r i g o - R e i n a et al.,Pharmac. Res.20,243,1988. 2} R . A r r i g o - R e i n a , Agents and Actions,30,210,1990.
Pholcodine is used as an antitussive agent. Although structurally related to morphine pholcodine does not have analgesic properties. The classification of pholcodine into narcotic drugs, however, restricts its marketing inside the European Union. Binding of pholcodine to opioid receptors has been only sporadically studied. Chert et al. (Life Sci. 48: 2165-2171, 1991) reported negligible binding of pholcodine to tJ opioid receptors (about 4700 times lower affinity than morphine). In this study we have confirmed the low affinity of pholcodine to p opioid receptors and report its even lower affinity to 8 opioid receptors. Synaptosomes (P2 fraction) prepared from whole brain (minus cerebellum) of adult male Wistar rats (Lazarus et al., J. Med. Chem. 35: 1222-1227, 1992) were used for the binding assays. Competition studies with pholcodine, morphine, DAMGO or DPDPE were conducted using 6 nM [aH]DPDPE and 3.5 nM [3H]DAMGO to label 6 and p sites, respectively. The non-specific binding was defined by displacing the label with 1.95 or 1.55 pM DPDPE or DAMGO, respectively. Competition curves were calculated by using non-linear regression analysis each combined from 3 to 5 assays using different synaptosome preparations. In this study we found that the pholcodine was about 1400 and 900 times less potent on opioid p and 8 receptors, respectively, than morphine. K opioid receptor binding studies ([3H]U69593 as ligand) are in progress. In conclusion, the antitussive effect of pholcodine cannot be related to p or 8 opioid receptors.
This work was supported by a Grant of MURST.
MONOCYCLIC COMPOUNDS STRUCTURALLY RELATED TO THE ~t-OPIOID AGONIST 3,8DIAZABICYCLO[3.2.1]OCTANES D. Barloceo1, G. Cignarella2, S. Villa2, L. Toma 3, W. Fratta4, P. Fadda4 1) Dip. Scienze Farmaceutiche, Universita' di Modena (Italy); 2) Ist. Chim. Farm. e Toss., Universita' di Milano (Italy); 3) Dip. Chimiea Organica, Universita' di Pavia (Italy); 4) Dip. Neuroseienze, Universita' di Cagliari (Italy)
I N H I B I T I O N BY M O R P H I N E , BUT NOT BY GABA, O F DIMETHYLPHENYLPIPERAZINIUM-INDUCED EMESIS IN CATS DoBoBeleslin and S.K.Krstid Department of Pharmacology, Faculty of Medicine and Department of Pharmacology, Faculty of Pharmacy, P.O.Box 662, 11000 Belgrade, Yugoslavia
We have recently proposed (1) a possible pharmaeophore for a new class of p,-selective opioid agonists of general structure 1. Besides the well known elements shared by most opiates (namely an aromatic system placed at an appropriate distance from a tertiary amine function) this model suggests the existence of a small hydrophobie pocket able to accept the endoethylenic bridge of DBOs moiety. To verify the importance of this requisite, we designed several monoeyclic derivatives (2,4) structurally related to 1 but lacking the endoethylenie bridge. In this contribute the modeling of the compounds is reported together with their chemical synthesis and their affinity for ~t receptors. Molecular modeling of 2-4 was performed by molecular mechanics calculations and allowed to determine their preferred conformations. Moreover, high field t H-NMR spectroscopy was used to confirm the results of the modeling.
The central inhibitory mechanisms subserving the emesis are still ill understood. Therefore, the aim of the present experiments was to study the effect of morphine and GABA on dimethylphenylpiperazinium (DMpP)-induced emesis in cats. In an aseptic operation under pentobarbital sodium (35-40 mg/kg i.p.) anaesthesia an infusion cannula was implanted into the left lateral cerebral ventricles of cats of either sex (2-4 kg) so that intracerebroventricular (ioc.v.) injections of drugs could be made without anaesthesia. In a separate series of experiments, the area postrema was destroyed electrolyticaUy. Only expulsion of the gastric content, was taken as a positive emetic response° In the first series of experiments, DMPP (1.0 nag) injected i°c.v. induced emesis in 83 % of cats, and even with highest doses of 2 nag never reached 100%o In the second series of experiments, the effect of morphine (0.005-0.05 rag) and GABA (0.5-1.0 nag), injected ioC.V° 20 minutes before the emetic challenge inhibited the emesis induced by DMPP (1:0 nag) similarly injected. In the third series of experiments i°eoVo DMPP (1 o0 rag) failed to evoke emesis in cats with ablated area postremao It is apparent that opioids, rather than GABA, might be a putative inhibitory neurotransmitters within the area postrema of the cat.
iR(R')
I
R'(R) 1
?H3
?H3
~_CH2~:(3R,) ~N_~NR(R') ~¢NR(R', I
R'(R) 2
R = COCH2CH3
l
R'(R) 3
I
R'(R) 4
R' = CH2CH=CHC6H~
l) E. Novellino et al., J. Comput.-Aided Mol. Design, 5, 335, 1991
--
116--