piperidines and metaphit

Our overall goal was to investigate the mechanism by which fentanyl attenuates acetylcholine-induced contraction in porcine coronary artery. We tested the hypothesis that fentanyl attenuates muscarinic coronary contraction via sigma receptor activation. Left coronary artery vascular rings were isolated from porcine hearts and were suspended in organ chambers for isometric tension recording. In untreated coronary vascular rings, acetylcholine administration resulted in dose-dependent contraction. Fentanyl attenuated acetylcholine-induced contraction. The sigma ligands--(+)-pentazocine, (+)-cyclazocine, haloperidol, and 1,3-di-o-tolylguanidine--also inhibited acetylcholine-induced contraction. In contrast, the selective sigma ligand, (+)-3-(3-hydroxyphenyl)-N-(1-propyl) piperidine failed to have an inhibitory effect on acetylcholine-induced contraction. Moreover, metaphit (1-[1(3-isothiocyanatophenyl)cyclohexyl]piperidine), which causes irreversible acylation of sigma receptors, only inhibited acetylcholine-induced contraction when it was present in the organ chamber. We also assessed the effects of inhibiting various points in the signal transduction pathway distal to naloxone-sensitive opioid receptor activation on acetylcholine-induced contraction. Selective (glybenclamide) and nonselective (tetraethylammonium) K(+)-channel inhibition, guanosine triphosphate-binding protein inactivation (pertussis toxin), and Type 1 and Type 2 dopamine receptor inhibition all failed to alter the attenuating effect of fentanyl on acetylcholine-induced contraction. Thus, neither sigma or opioid receptor activation is a prerequisite for fentanyl-induced inhibition of muscarinic coronary contraction.

Topics: Acetylcholine; Anesthetics, Intravenous; Animals; Coronary Vessels; Cyclazocine; Dopamine Agonists; Dopamine Antagonists; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Fentanyl; Guanidines; Haloperidol; Muscarine; Muscarinic Agonists; Narcotic Antagonists; Narcotics; Pentazocine; Phencyclidine; Piperidines; Potassium Channel Blockers; Receptors, Dopamine; Receptors, sigma; Signal Transduction; Swine; Vasoconstriction; Vasoconstrictor Agents; Vasodilator Agents

The ion channel probe phencyclidine [1-(1-phenylcyclohexyl)piperidine; PCP] selectively inhibited aggregation, secretion and ultrastructural changes in platelets induced by adrenaline, but did not affect activation induced by other common platelet agonists such as alpha-thrombin, ADP, collagen or ionophore A23187. [3H]PCP bound to platelets with high affinity (Kd 134 +/- 33 nM; 3600 +/- 1020 sites/platelet), as did the thienyl analogue [3H]TCP (1-[1-(2-thienyl)cyclohexyl]piperidine). PCP binding to platelets was increased 3-4-fold in N-methylglucamine buffer in the absence of Na+ ions. Binding was unaffected by haloperidol and was only weakly inhibited (EC50 10-20 microM), without significant stereoselectivity by the two sets of stereoselective ligands, dexoxadrol/levoxadrol and (+)MK801/(-)MK801. Binding of PCP was not competed for by adrenaline or yohimbine. Only the high-affinity binding of [3H]PCP to platelets was blocked by prior treatment of the platelets with the covalent affinity probe Metaphit, and these platelets no longer aggregated in response to adrenaline although they responded normally to alpha-thrombin, ADP and collagen. These results suggest that platelets contain high-affinity receptors for PCP that can modulate adrenaline-induced platelet activation.

Topics: Binding, Competitive; Blood Platelets; Cells, Cultured; Chromatography, Gel; Cyclic AMP; Dioxolanes; Dizocilpine Maleate; Epinephrine; Humans; Phencyclidine; Piperidines; Platelet Activation; Receptors, Neurotransmitter; Receptors, Phencyclidine

Isothiocyanate derivatives of (-)-cocaine were prepared and tested for inhibitory potency at the cocaine receptor in rat striatal membranes. Coincubation with m-isothiocyanatobenzoylecgonine methyl ester (m-ISOCOC), p-isothiocyanatobenzoylecgonine methyl ester (p-ISOCOC), and 3 beta-(4-isothiocyanatophenyl)tropane-2-carboxylic acid methyl ester (ISOWIN) resulted in inhibition of [3H]WIN 35,428 binding, but the compounds were about 10-fold weaker than (-)-cocaine. However, p-ISOCOC was approximately 3-fold more potent than metaphit, an isothiocyanate derivative of phencyclidine. p-ISOCOC was equipotent at the serotonin transporter but was much less potent at the norepinephrine transporter and was inactive at the D2 dopamine receptor at 1000 microM concentration. The IC50 value for m-ISOCOC and p-ISOCOC varied with tissue concentration, suggesting irreversible inhibition of binding. Preincubation with m-ISOCOC and p-ISOCOC resulted in inhibition of [3H]WIN 35,428 binding that could not be removed by washing of the membranes; in contrast, preincubation with (-)-cocaine caused inhibition that was readily removed by washing. Preincubation with 1 microM concentrations of p-ISOCOC resulted in a large reduction in Bmax of the high affinity binding site for [3H]WIN 35,428. Preincubation with 100 microM p-ISOCOC eliminated the high affinity site and apparently reduced the affinity at the low affinity site. Coincubation of 10 microM p-ISOCOC with 100 microM cocaine prevented the total loss of [3H]WIN 35,428 binding. The uptake of [3H]dopamine was inhibited by p-ISOCOC with an IC50 comparable to that of cocaine. Additionally, preincubation of rat striatal synaptosomes with 10 microM p-ISOCOC reduced the Vmax of [3H]dopamine uptake after washing. These data suggest that m-ISOCOC and p-ISOCOC are useful irreversible acylators of (-)-cocaine binding sites at the dopamine transporter.

Topics: Animals; Benzamides; Binding, Competitive; Brain Stem; Carrier Proteins; Cerebral Cortex; Cocaine; Corpus Striatum; Dopamine; Dopamine Plasma Membrane Transport Proteins; In Vitro Techniques; Ligands; Male; Mazindol; Membrane Glycoproteins; Membrane Transport Proteins; Nerve Tissue Proteins; Paroxetine; Phencyclidine; Piperidines; Rats; Rats, Inbred Strains; Thiocyanates

Pretreatment of guinea pig brain membranes with 1-[1-(3-isothiocyanatophenyl)cyclohexyl]piperidine (Metaphit) caused irreversible and differential inhibition of ligand binding to sigma (sigma) receptors. The concentration of Metaphit required to produce 50% inhibition of binding of [3H]1,3-di-o-tolylguanidine ([3H]DTG), [3H](+)-3-(3-hydroxy-phenyl)-N-(1-propyl)piperidine ([3H](+)-3-PPP), and [3H](+)-N-allylnormetazocine ([3H](+)-SKF 10,047) to sigma receptors was 2, 10 and 50 microM, respectively. This compares to a value of 10 microM for inhibition of [3H]1-[1-(2-thienyl)cyclohexyl]piperidine [( 3H]TCP) binding to phencyclidine (PCP) receptors. While Metaphit was an irreversible, non-competitive inhibitor at PCP receptors, this compound produced irreversible, competitive inhibition at sigma receptors.

Topics: Acylation; Animals; Behavior, Animal; Brain Chemistry; Electrophysiology; Guinea Pigs; In Vitro Techniques; Membranes; Phencyclidine; Piperidines; Rats; Receptors, Neurotransmitter; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Phencyclidine

Etoxadrol-meta-isothiocyanate (2S,4S,6S-2-ethyl-2-(3-isothiocyanatophenyl)-2-piperidyl)1,3-dioxolane, 4a) has been synthesized and characterized as an irreversible ligand for the phencyclidine (PCP)-binding site. It is the first chiral electrophilic affinity ligand for this site to have been described. This affinity ligand is based upon etoxadrol, a 1,3-dioxolane known to have PCP-like effects in vivo and in vitro. Etoxadrol-meta-isothiocyanate was found to be four-five times more potent in vitro than metaphit (1-[1-(3- isothiocyanatophenyl)cyclohexyl]piperidine), the only previously known electrophilic affinity ligand for the PCP-binding site. The binding was shown to be highly enantioselective for etoxadrol-meta-isothiocyanate (4a). The 2R,4R,6R-enantiomer of 4a was essentially inactive. The ability of the 2S,4S,6S-enantiomer (4a) to interact with the benzodiazepine, muscarinic, and mu opioid receptor systems was also examined, and it was found not to interact with these receptor systems. It seems likely that 4a will prove to be a valuable tool in the study of structure and function of the PCP-binding site.

Topics: Acylation; Animals; Binding, Competitive; Brain; Chemical Phenomena; Chemistry; Dioxolanes; Phencyclidine; Piperidines; Rats; Receptors, GABA-A; Receptors, Muscarinic; Receptors, Neurotransmitter; Receptors, Opioid; Receptors, Opioid, mu; Receptors, Phencyclidine; Stereoisomerism

The interactions of phencyclidine (PCP) and related agonists with putative receptor blockers were studied on cerebellar Purkinje neurons using electrophysiological techniques. Depressions induced by PCP or dexoxadrol, a sigma receptor agonist, were markedly antagonized by the PCP receptor antagonist metaphit, which acylates PCP receptors via its isothiocyanate moiety. Conversely, the depressant effect of levoxadrol, the (-) isomer of dexoxadrol, was not affected by metaphit. Further evidence that metaphit's specific antagonism of dexoxadrol- and PCP-mediated depressions was derived from data showing that drugs which respectively acylate mu and delta opioid receptors, benzimidazole isothiocyanate and fentanyl isothiocyanate, do not antagonize the actions of either PCP or dexoxadrol. Moreover, tyramine, which like PCP acts as an indirect norepinephrine agonist, is not antagonized by metaphit. These observations support the concept that metaphit causes a pharmacologically specific and irreversible antagonism of the effects of both PCP and dexoxadrol in the cerebellum. Thus, the electrophysiological mechanisms of PCP actions are similar to those triggered by sigma opioid agonists in this brain area.

Topics: Animals; Cerebellum; Dioxolanes; Drug Interactions; Electrophysiology; Isomerism; Male; Phencyclidine; Piperidines; Purkinje Cells; Rats; Rats, Inbred Strains; Receptors, Opioid; Receptors, sigma; Substrate Specificity