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Biomedical subjects

E J Simon

Publications and source records attributed to E J Simon.

At least 109 records · Page 6Linked to original sources
PubMed1984

A novel phencyclidine analog interacts selectively with mu opioid receptors.

A new potent analgesic drug, 1-(1-phenylcyclohexyl)-4-phenyl-4-piperidinol (PCP-4-Ph-4-OH), derived from phencyclidine was tested for its interactions with different types of opioid receptors. The antinociceptive effect of PCP-4-Ph-4-OH in the mouse writhing test (ED50 = 0.3 mg/kg) is reversed by low doses of naloxone (pA2 = 6.98). The potency of PCP-4-Ph-OH in the inhibition of the electrically induced contractions of the guinea-pig ileum (IC50 = 17 nM) is 8-fold higher than that in the mouse vas deferens preparation (IC50 = 130 nM). The concentration of naloxone required to double the IC50 (Ke) of PCP-4-Ph-4-OH is 1.5 to 1.9 nM in both preparations. In opioid radioreceptor assays, PCP-4-Ph-4-OH displays 60- to-300 fold higher affinity for the [3H] dihydromorphine (mu) and D-[3H]Ala2-MePhe-Gly-ol5-enkephalin (mu) binding sites than for D-[3H]Ala2-D-Leu5-enkephalin (delta) sites in rat brain and [3H]bremazocine (kappa) sites in guinea-pig cerebellar membrane preparations. These results suggest that PCP-4-Ph-4-OH interacts with high affinity and selectivity with mu opioid receptors.

Analgesia↗
PubMed1984

Characterization of the selective inhibition of the delta subclass of opioid binding sites by alcohols.

We recently reported that ethanol and other aliphatic alcohols exert a selective inhibition on the binding of enkephalins to delta opioid binding sites. We report here a more detailed investigation of the characteristics of this inhibition. Opioid binding sites of the kappa subtype are similar to mu opioid binding sites in their relative insensitivity to inhibition by aliphatic alcohols. Scatchard analysis of saturation data of enkephalin binding showed that inhibition is the result of a decrease in affinity. Results of kinetic experiments demonstrated that the inhibition can be entirely accounted for by an increase in the dissociation rate of the ligand-receptor complex. The presence of sodium ions in the incubation medium and raising the temperature of incubation exacerbate the inhibitory effectiveness of alcohols. The order of potency among structural isomers of alcohols for inhibition of delta receptor binding is as follows: straight-chain primary greater than isoprimary greater than secondary greater than tertiary. The order of inhibitory potency of the aliphatic alcohols tested correlates well with their ability to disorder the cell membrane lipid bilayer. It is suggested that this is a probable mechanism by which alcohols inhibit binding to delta opioid binding sites.

Alcohols↗
PubMed1983

Evidence for the solubilization of multiple opioid binding sites from mammalian brain.

Good yields of 3H-opioid agonist binding in solution have been obtained following fractionation of brain membrane extracts on sucrose density gradients. The presence of multiple opioid binding sites was demonstrated for extracts from rat and guinea pig brain. Fractionation of solubilized material from guinea pig brain resulted in the separation of the peak of 3H-bremazocine binding (in the presence of DAGO and DADL) from the peaks of binding of tritiated mu and delta agonists. These results suggest that the kappa binding site may represent a separate molecular species from mu and delta opioid binding sites.

Animals↗
PubMed1983

Quaternary derivatives of narcotic antagonists: stereochemical requirements at the chiral nitrogen for in vitro and in vivo activity.

We have studied three pairs of diastereoisomers of quaternary narcotic antagonists and their parent tertiary amines, levallorphan, nalorphine and naloxone, to see how configuration about the chiral nitrogen affects in vitro and in vivo activity. In each series only the diastereoisomer obtained by methylation of the N-allyl substituted tertiary amine (N-methyl diast.) was potent in displacing 3H-naltrexone from rat brain membranes (Ki 10(-8) - 10(-7)M) and as pure morphine antagonist in the guinea-pig ileum (Ki 10(-8)-10(-7)M). Conversely, diastereoisomers obtained by reacting N-methyl substituted tertiary amines with allyl halide (N-allyl diast.) did not displace 3H-naltrexone, up to 10(-6)M, and had negligible antagonist activity and slight agonist action in the guinea-pig ileum. In vivo findings (charcoal meal transit test in mice) were generally consistent with those in vitro. Thus only the N-methyl but not the N-allyl diast. inhibited morphine constipation and behaved as pure antagonists.

Animals↗
PubMed1983

The role of opioids in feeding and reward elicited by lateral hypothalamic electrical stimulation.

We have previously shown that feeding induced by electrical stimulation in the lateral hypothalamus of rats is inhibited by naloxone but not its quaternary analogue. In the present study, effects of morphine and loperamide -an opiate that does not pass the blood-brain barrier- were examined. Loperamide inhibited stimulation-induced feeding; reversal of this effect by quaternary naloxone confirmed the peripheral site of action. A low dose of morphine (1.25 mg/kg) facilitated feeding but higher doses were inhibitory. An inhibitory dose of morphine became facilitory, however, when preceded by quaternary naloxone. It therefore appears that central opioid activity promotes ingestive behavior while peripheral activity inhibits ingestion. To evaluate the function served by the central facilitory process, we exploited the relation that exists between feeding and self-stimulation elicited through a common electrode. It was found that potentiation of self-stimulation by food deprivation is blocked by naloxone. It is concluded that endogenous opioid activity may promote feeding by enhancing the reward value of food as a function of hunger.

Animals↗
PubMed1983

Evidence from opiate binding studies that heroin acts through its metabolites.

The relative affinity to opiate receptors of heroin, 6-acetylmorphine and morphine was estimated by determining their ability to displace specifically bound 3H-naltrexone from rat brain opiate binding sites. In vitro hydrolysis of heroin to 6-acetylmorphine was monitored in the binding assay filtrate by use of a quantitative HPLC procedure. The rate of heroin hydrolysis was significantly slower at 0 degrees C than at 37 degrees C. The displacement of 1 nM 3H-naltrexone by unlabeled ligand at concentrations ranging from 7 to 500 nM was measured at 0 degrees C for 120 minutes, yielding IC50 values of heroin = 483 nM, 6-acetylmorphine = 73 nM and morphine = 53 nM. When the binding data for heroin were recalculated to include the displacement that could be attributed to the 6-acetylmorphine derived from heroin degradation during the incubation, all of the apparent heroin binding was accounted for by the 6-acetylmorphine. These results are consistent with previous reports of the low binding affinity of morphine congeners (e.g., codeine) that lack a free phenolic 3-hydroxyl group and support the view that heroin is a prodrug which serves to determine the distribution of its intrinsically active metabolites, 6-acetylmorphine and morphine.

Animals↗
PubMed1983

Effects of naloxone and its quarternary analogue on stimulation-induced feeding.

Feeding was induced in rats by electrical stimulation in the lateral hypothalamus. Naloxone (0.2 and 1.0 mg/kg) produced a dose-related elevation of the frequency threshold for stimulation-induced feeding while quarternary naloxone (2.0 and 10.0 mg/kg) had no effect. Since quarternary naloxone does not readily penetrate the blood-brain barrier, we conclude that the opiate receptors at which naloxone exerts its anorectic action are located in the brain rather than in potential peripheral tissues such as gastrointestinal tract, pancreas or adrenal medulla. The threshold-elevating effect of naloxone only became marked after rats had engaged in one or two 5-sec bouts of feeding. The effect continued to increase following each subsequent bout of feeding. Naloxone therefore appears to inhibit feeding by interacting with post-ingestive factors.

Animals↗
PubMed1982

Mu and kappa opioid agonists elevate brain stimulation threshold for escape by inhibiting aversion.

Rats were trained to press a lever to escape electrical stimulation of the nucleus reticularis gigantocellularis and to obtain stimulation of the lateral hypothalamus. Morphine sulfate and ethylketocyclazocine (EKC) both elevated the intensity of stimulation required to sustain escape at doses which did not affect self-stimulation. Parallel dose-response lines were obtained for the two opioid agonists but the effect of EKC was more resistant to naloxone antagonism. These results suggest that both mu-and chi-sub-types of opiate receptor mediate the inhibition of supraspinally-elicited aversion.

Animals↗
PubMed1982

Exposure to 4-aminopyridine prevents depressant effects of opiates on sensory-evoked dorsal-horn network responses in spinal cord cultures.

The depressant effects of morphine (0.1-1 microM) on sensory-evoked dorsal-horn network responses in explants of mouse spinal cord with attached dorsal root ganglia (DRGs) were rapidly restored after addition of 4-aminopyridine (4-AP; 0.1 mM) and major components of these cord responses were stably maintained in the presence of the opiate. Moreover, prior exposure of cord-DRG explants to 0.1 mM 4-AP prevented the depressant effects of 0.1 microM morphine on DRG-evoked dorsal-horn responses, and the effects of 1-10 microM morphine were at least partly antagonized. Increased Ca++ levels (5 microM) attenuated the depression of dorsal horn responses by 1-10 micro M morphine and these effects of Ca++ were greatly enhanced in the presence of 4-AP--in some cultures, concentrations of morphine as high as 100 micro M were strongly antagonized during test periods up to 2 hours. Receptor assays showed that 0.1 mM 4-AP +/- 5 mM Ca++ had no effect on stereospecific opiate binding, indicating that the antagonist actions of these agents in our cultures do not occur at the level of the opiate receptor. The relevance of our in vitro studies of 4-AP antagonism of opiate-depressant effects on sensory-evoked dorsal-horn network responses for analyses of problems in opiate analgesia has been strengthened by a recent report demonstrating that 4-AP does, in fact, reverse morphine analgesia in rats, as determined by tail flick tests.

4-Aminopyridine↗
PubMed1982

Inactivation and solubilization of opiate receptors by phospholipases A2.

(1) As previously shown, stereospecific binding of opiates to membrane bound receptors is inhibited by treatment with small amounts of phospholipase A2 from Vipera russelli. This effect is quantified and compared with the enzymes from the venoms of Naja Naja siamensis, Apis Mellifica and from porcine pancreas. All enzymes are equally effective. The inhibition is due to partial phospholipid hydrolysis leading to inactivation of membrane-bound receptor. (2) Bee venom phospholipase A2 together with the synergistically acting peptide, melittin, causes receptor solubilization up to 80% of preformed receptor-ligand complex can be solubilized in this manner. (3) Lysophosphatidylcholine, a product of phospholipid hydrolysis, solubilizes performed receptor-ligand complex to a similar extent. Several other detergents were tested for their ability to solubilize receptor-ligand complex. Digitonin appears to be most effective in solubilizing such a complex.

Animals↗
PubMed1982

Potential affinity labels for the opiate receptor based on fentanyl and related compounds.

Derivatives of fentanyl, 3-methylfentanyl, sufentanil, and lofentanil, possessing chemo- or photoaffinity functionalities, were synthesized as potential affinity reagents for the opiate receptor. Opiate receptor binding constants (IC50) were determined in competition experiments with [3H]naloxone and [3H]naltrexone. Affinity-labeling experiments were generally unsuccessful, although some irreversible attachment was achieved with alpha-diazoamide 17 and aryl azide 23.

Affinity Labels↗
PubMed1982

Solubilization and characterization of active opiate binding sites from mammalian brain.

Active binding sites have been solubilized from cell membranes derived from mammalian brain. High affinity, stereospecific binding to soluble sites was demonstrable when membranes from rat brain, human frontal cortex and bovine corpus striatum were treated with digitonin or glycodeoxycholate, provided that the binding assay was conducted at 25 degrees C or below and in the presence of 50 to 100 mM NaCl. The yield of solubilized binding sites extracted from brain cell membranes was increased substantially (up to 43% yield from bovine striatum) when membranes were treated with detergent solutions containing 0.5 to 1.0 M NaCl. This effect was not observed when LiCl, KCl or (NH4)2SO4 were substituted for NaCl. Evidence for the solubility of the binding sites was provided by two criteria: nonsedimentation after 2 hr of centrifugation at 10(5) X g and an apparent molecular weight of 3 to 4 X 10(5) as determined by gel filtration.

Animals↗
PubMed1981

Multiple opiate receptors: alcohol selectively inhibits binding to delta receptors.

The addition of ethanol or other aliphatic alcohols to rat brain membranes strongly inhibits binding of enkephalins at concentrations at which little inhibition of opiate alkaloids is seen. Inhibition is reversible, and potency increases with chain length of the alcohol. The results suggest that delta receptors are considerably more sensitive to alcohols than mu receptors. This is the first demonstration of selective inhibition of one of the postulated classes of opiate receptors by a reagent that is not a ligand for the receptor.

Alcohols↗