Biomedical subjects

Y Sarne

Publications and source records attributed to Y Sarne.

At least 37 records · Page 2Linked to original sources

PubMed1993

The involvement of sodium ions in the positive inotropic effect of naloxone.

1. The opiate antagonist naloxone induces a positive inotropic effect in isolated cardiac muscles. 2. The response to naloxone is dependent on the presence of Na+ in the bathing solution, is proportional to the rate of electrical stimulation, and increased in the presence of veratridine. 3. Lowering [K+]o to 50% augments the response, while complete removal of K+ from the extracellular solution attenuates the response to naloxone. 4. Maximal concentration of naloxone decreases the inotropic effect of the cardiac glycoside ouabain. 5. The results indicate the involvement of intracellular sodium accumulation in the positive inotropic effect of naloxone, probably through the inhibition of the sarcolemmal Na(+)-K+ pump.

Animals↗

PubMed1993

Morphine inhibits calcium influx and the response to acetylcholine in Xenopus oocytes.

Incubation of intact Xenopus oocytes with the opioid radioligand [3H]diprenorphine (0.5 nM) resulted in specific binding of 1.7 +/- 0.3 fmol per oocyte. Morphine (10 microM) inhibited the uptake of 45Ca2+ into the oocyte by 66 +/- 9%. The opioid antagonist naltrexone partially blocked this effect of morphine. Preincubation of oocytes with morphine (10 microM, 2 min) partially inhibited the fast and slow responses of the oocyte to acetylcholine by 26 and 52%, respectively. We conclude that native Xenopus oocytes possess opioid receptors that may modulate the muscarinic response by limiting calcium influx into the cell.

Acetylcholine↗

PubMed1993

Selective and interactive down-regulation of mu- and delta-opioid receptors in human neuroblastoma SK-N-SH cells.

Human neuroblastoma SK-N-SH cells, which contain both mu- and delta-opioid receptors, were grown under conditions that provided a mu:delta ratio of 1.5:1. Both receptors were down-regulated after 72 hr of exposure to 100 nM etorphine. Selective down-regulation was demonstrated using selective opioid agonists; the mu agonist Tyr-D-Ala2-Gly-(Me)Phe4-Gly-ol down-regulated mu- but not delta-opioid receptors, whereas prolonged exposure to the selective delta agonist D-Pen2,D-Pen5-enkephalin resulted in delta- but not mu-opioid receptor down-regulation. Morphine, which binds mu- as well as delta-opioid receptors, down-regulated both receptor subtypes. NG108-15 cells, which contain delta receptors exclusively, were also tested. NG108-15 cells did not exhibit delta-opioid receptor down-regulation when exposed to morphine. The discrepancy between the effect of chronic morphine treatment on delta receptors in SK-N-SH cells and in NG108-15 cells raised the question of whether the coexistence of mu receptors in the former allowed morphine to down-regulate delta receptors. The role of mu-opioid receptors in morphine-induced delta receptor down-regulation was studied by using the irreversible mu antagonist beta-funaltrexamine. Pretreatment of SK-N-SH cells with beta-funaltrexamine prevented down-regulation of delta receptors in response to chronic exposure to morphine but did not affect down-regulation of delta receptors in response to D-Pen2,D-Pen5-enkephalin. The experimental data indicate that morphine-induced delta-opioid receptor down-regulation is dependent on the presence of functional mu receptors in the same cell.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1992

The effect of opiate agonists and antagonists on Na(+)-Ca2+ exchange in cardiac sarcolemma vesicles.

Opiate agonists and antagonists inhibit Na(+)-Ca2+ exchange in the isolated cardiac sarcolemma vesicles. Non-opioid stereoisomers (dextrorphan, Mr 1542MS, WIN 44,441-3) display effects similar to their opioid isomers (levorphanol, Mr 1543MS, WIN 44,441-2) suggesting that inhibition is not mediated by opiate receptors. Naloxone (permeable) and methylnaloxone (impermeable) inhibit the Na(+)-Ca2+ exchange similarly, suggesting an extravesicular location of inhibitory site. The inhibitory potency of naloxone is pH-independent in the range of 7.4-9.1, suggesting that the charge-carrying properties of drug-protein interactions are not altered under the tested conditions. Opiates display similar dose-response relationships for Na(+)-Ca2+ exchange and its partial reaction, the Ca(2+)-Ca2+ exchange. The opiate-induced inhibition is complete and noncompetitive in regard to extravesicular calcium. These data suggest that opiates do not bind to the Ca(2+)-binding domain (A-site), but they may interest either with the Na(+)-binding site (B-site) or with a putative opiate-binding site, presumably located outside of the ion-binding vicinity. Further studies on structure-activity relationship might lead to the discovery of potent and more specific inhibitors of cardiac Na(+)-Ca2+ exchanger. A possible relevance of these findings to some non-opioid pharmacological effects of naloxone on the cardiac muscle is suggested.

Animals↗

PubMed1992

Nonopioid effect of morphine on electrically evoked acetylcholine release from Torpedo electromotor neurons.

The release of acetylcholine from Torpedo electric organ slices following their electrical stimulation was modulated by morphine, by the muscarinic antagonist atropine, and by the nicotinic antagonist tubocurarine. Addition of either atropine or tubocurarine in the presence of the acetylcholinesterase inhibitor phospholine iodide enhanced acetylcholine release. The effects of the two antagonists were additive, a result suggesting that the secreted acetylcholine regulates its own release by activating both muscarinic and nicotinic cholinergic receptors and that these receptors inhibit acetylcholine release by different mechanisms. The effects of opiates on acetylcholine release were examined under conditions in which the cholinergic modulation of release is blocked, i.e., in the presence of atropine and tubocurarine. These experiments revealed that electrically evoked release of acetylcholine is blocked by the opiate agonists morphine and levorphanol. However, the inhibitory effect of morphine on acetylcholine release was not reversed by the opioid antagonist naloxone. Furthermore, dextrorphan, the nonopioid stereoisomer of levorphanol, had the same inhibitory effect as its opioid counterpart. These findings suggest that the effects of opiates on electrically evoked release of acetylcholine are not mediated by opioid receptors. The possible mechanisms underlying these nonopioid effects of morphine and levorphanol are discussed.

Acetylcholine↗

PubMed1991

Effect of opioid peptides on electrically evoked acetylcholine release from Torpedo electromotor neurons.

The opioid peptide dynorphin A(1-8) (1 micron) increased acetylcholine release from the Torpedo electric organ by approximately twofold. This effect was reversed by the opiate antagonist naloxone. The effect of Dyn A(1-8) on acetylcholine release was found to vary in magnitude with the seasons of the year, with maximal enhancement being observed in the summer and none in winter. Dynorphin B, methionine-enkephalin and leucine-enkephalin also increased acetylcholine release and showed similar seasonal variations. These findings suggest that acetylcholine release from Torpedo electromotor neurons is regulated by opiate receptors. The physiological significance of these observations is discussed in view of the previous findings that the Torpedo neurons contain an endogenous enkephalin-like peptide.

Acclimatization↗

PubMed1991

EO-199, a specific antagonist of antiarrhythmic drugs: assessment by binding experiments and in vivo studies.

EO-199, a demethylated analog of the novel class I antiarrhythmic drug EO-122 was found to antagonize the antiarrhythmic activity of EO-122 and that of procainamide (Class IA). EO-199 did not block significantly the activity of a class IB antiarrhythmic agent, lidocaine. EO-199 also displaced the specific binding of [3H]EO-122 to rat heart membranes similarly to procainamide whereas lidocaine did not. The correlation between binding experiments and pharmacological effects points to a possible subclassification of these drugs; the two chemical analogs EO-199 and EO-122, as well as procainamide (IA) but not lidocaine (IB), compete at the same site or the same state of the sodium channel. The availability of a specific antagonist might be useful for studying the mechanism of action of antiarrhythmic drugs as well as an antidote in cases of antiarrhythmics overdose intoxication.

Animals↗

PubMed1991

Effect of beta-endorphin on human chorionic gonadotrophin secretion by placental explants.

In the present study the effect of physiological concentrations of beta-endorphin was examined upon human chorionic gonadotrophin (HCG) secretion by first trimester placental explants. Results show that at 7-9 weeks of gestation, beta-endorphin inhibited HCG secretion; a maximal suppression of 60% was noted at 5 x 10(-10) M concentrations, while fivefold lower or higher doses were less effective. This inhibitory effect was completely reversed by naloxone, an opiate receptor antagonist, indicating involvement of an opiate receptor in the action of beta-endorphin. The opioid peptide specificity was demonstrated by the failure of N-acetyl-beta-endorphin, a non-opiate analogue used at the same concentration range, to affect HCG secretion. Following the HCG peak, at 11 weeks however, the effect of beta-endorphin was stimulatory on HCG secretion, which suggests a gestational age-dependent effect of the opioid peptide. In conclusion, these data indicate that beta-endorphin, a mu and delta opioid receptor ligand, has a modulatory effect on HCG secretion in vitro in the young placenta.

Chorionic Gonadotropin↗

PubMed1991

Anti-arrhythmic activities of opioid agonists and antagonists and their stereoisomers.

1. A series of opioid agonists, antagonists and their (+)-stereoisomers were tested for antiarrhythmic activity in the rat coronary artery occlusion model. 2. Naloxone (0.01-2 mg kg-1) significantly reduced the incidence and severity of cardiac arrhythmias, in accordance with previous published studies. 3. The non-opioid stereoisomer, (+)-naloxone, was equipotent with naloxone against occlusion-induced arrhythmia. 4. Similar non-stereospecific antiarrhythmic effects were induced by another opioid antagonist, Win 44,441-3 and its stereoisomer Win 44,441-2. 5. The opioid agonists, morphine and levorphanol, protected against occlusion-induced arrhythmia as did the opioid antagonists, and the (+)-stereoisomer, dextrorphan, was equipotent to levorphanol. 6. It is concluded that the antiarrhythmic effects of opioid drugs are not mediated by opioid receptors. A direct effect on ionic currents in cardiac muscle is suggested as the mechanism of opioid antiarrhythmic activity.

Animals↗

PubMed1991

The effect of dynorphin on placental pulsatile human chorionic gonadotropin secretion in vitro.

Using in vitro methods we have studied the effect of dynorphin (DYN) a natural k opioid receptor ligand upon hCG secretion in the first trimester placenta. In superfusion, where we have recently reported that hCG secretion is episodic, we found that the addition of 1-min pulses of DYN had a significant stimulatory effect upon pulsatile hCG secretion. This effect was seen at concentrations of 10(-8) mol/L-10(-11) mol/L. Higher doses (10(-6) mol/L) and lower doses (10(-12) mol/L) were ineffective. A 10-min administration was more effective than the 1-min pulses. Prolonged administration (90 min) caused an initial increase in pulsatile hCG secretion which was followed by a decrease to control values. However, upon stopping the prolonged opiate administration there was a substantial increase in hCG secretion. The involvement of opioid receptors in mediating the effect of DYN on hCG release was demonstrated by using naloxone, an opioid receptor antagonist. Coadministration of DYN, 10(-11) mol/L, and naloxone, 10(-10) mol/L, reduced markedly the effect of DYN. This was followed by a delayed increase in hCG secretion. Furthermore, des-tyrosine-DYN, the nonopioid derivative of DYN was 1000 times less potent in stimulating hCG release than DYN. The involvement of DYN in physiological control of placental hCG secretion is suggested.

Activity Cycles↗

PubMed1988

Antiarrhythmic action of naloxone: direct, non-opiate effect on the rat heart.

The opiate antagonist naloxone reduced the incidence and severity of cardiac arrhythmia induced in rats by intracarotid administration of adrenaline. Naloxone also reversed the adrenaline-induced arrhythmia in isolated heart preparations, suggesting a local antiarrhythmic action of the opiate antagonist. Similar effects were obtained with the (+) stereoisomer of naloxone which is inactive as an opiate antagonist. Thus, the direct action of naloxone at the rat heart is probably not mediated by opiate receptors.

Animals↗

PubMed1987

Biphasic competition between opiates and enkephalins: does it indicate the existence of a common high affinity ("mu-1") binding site?

Displacement from brain membranes of labeled opiates by low concentrations of enkephalins and of labeled enkephalins by low concentrations of opiates has been previously explained by the existence of a common high affinity site termed mu-1. An alternative interpretation of the same results is that the trough seen in the low concentration zone of the displacement curves represents cross binding of mu and delta opioid ligands to delta and mu receptors, respectively. In three sets of experiments with brain membranes, the size of the trough is shown to be dependent on the labeled ligand used: The ratio between the size of troughs seen with [3H]D-Ala, D-Leu enkephalin and with [3H]morphine varies with experimental conditions (storage of membranes at 4 degrees C for 72 h), with ratio of mu:delta receptors (e.g. in thalamus and cortex which are enriched in mu and delta sites, respectively) and with pretreatment of membranes with naloxonazine. These results can not be explained by a common high affinity site, but rather by binding of [3H]D-Ala, D-Leu enkephalin to mu and of [3H]morphine to delta opioid receptors.

Animals↗

PubMed1987

Nonopiate effect of naloxone on cardiac muscle contractility.

To test the hypothesis that naloxone exerts a direct positive inotropic effect on the cardiac muscle, we employed two in vitro models. In one set of experiments we demonstrated that injection of 1 mg naloxone into an isolated perfused rat heart produced a significant increase in the amplitude of contraction. In another set of experiments we exposed an isolated and spontaneously contracting rat right atrium in a tissue bath to naloxone, and demonstrated that the amplitude of contraction increased significantly within a few minutes of naloxone administration. We showed that this effect of naloxone was not related to opiate receptors, since a similar effect was obtained with d-naloxone (the stereoisomer that is inactive as an opiate antagonist) and it was not affected by pretreatment with morphine. We also demonstrated that addition of alpha- and beta-adrenergic antagonists phentolamine and propranolol, in doses that effectively block alpha- and beta-adrenergic agonists, did not have any effect on naloxone's inotropic action. We validated our results in two electrically driven strips of human atrial myocardium in the tissue bath. A positive inotropic response to naloxone, measured as an increase of 80 and 50% in the amplitude of contraction, was noted. We postulate that naloxone's previously described cardiovascular pressor effect in states of shock may not only be related to reversal of the effects of endorphins but also to its direct inotropic action.

Animals↗

PubMed1986

Identification of distinct binding site subunits of mu and delta opioid receptors.

Iodinated human beta-endorphin was affinity-cross-linked to opioid receptors present in membrane preparations from bovine frontal cortex, bovine striatum, guinea pig whole brain, and rat thalamus. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography revealed covalently labeled peptides of 65, 53, 41, and 38 kilodaltons (kDa). The 65- and 38-kDa peptides were present in all four tissues. The 41-kDa peptide was seen only in bovine caudate and guinea pig whole brain while the 53-kDa peptide was absent in rat thalamus. All four labeled peptides were constituents of opioid receptors since their labeling was fully suppressed by the presence of excess opiates, such as bremazocine, during binding. The distribution and levels of the labeled species in the brain tissues examined and, in earlier work, in the neuroblastoma X glioma NG 108-15 cell line suggested that the 65-kDa peptide is a binding component of mu receptors while the 53-kDa peptide is a binding subunit of delta receptors. This result was strongly supported by the finding that the labeling of the 65-kDa peptide is selectively reduced by the presence of the highly mu-selective ligand Tyr-D-Ala-Gly-(N-Me)Phe-Gly-ol (DAMGE) during binding, while while the labeling of the 53-kDa peptide is selectively reduced or eliminated by the highly mu-selective ligand [D-Pen2, D-Pen5]enkephalin (DPDPE). The labeling of the 41- and 38-kDa bands was reduced by either DAMGE or DPDPE. The relationship of these lower molecular weight opioid-binding peptides to mu and delta receptors is not understood. Several possible explanations are presented.

Animals↗

PubMed1985

Stress induced analgesia: its opioid nature depends on the strain of rat but not on the mode of induction.

Reports by several investigators have shown that both opioid and non-opioid analgesia can be induced by non-pharmacological manipulations such as the administration of electric shock, and that such analgesia depends on shock parameters, the affective state of the animal and the region of the body shocked. We tested several manipulations which have been reported to induce opioid analgesia using a local strain of rats (CR). Such manipulations included the used of 30 min of intermittent footshock (3 mA, 1 s on, 5 s off), brief shock to the forepaws, transpinal electroconvulsive shock (ECS) and tail shock induced helplessness. Administration of either naloxone or naltrexone to rats of the CR strain failed to attenuate the analgesic effect of these manipulations and in some cases even enhanced analgesia. The existence of functional opioid analgesia systems in CR rats was evident from the fact that electrical stimulation of the periaqueductal gray area produced naloxone sensitive analgesia. In additional experiments we compared the analgesic effect of brief continuous (3 min) footshock, prolonged intermittent footshock (30 min) and ECS in young (less than 75 days of age) and old (greater than 75 days of age) rats of the Sabra strain. Young Sabra rats showed naloxone sensitive analgesia following all 3 manipulations while adult rats displayed analgesia which was naloxone insensitive. Furthermore, no decrement in learning, indicative of helplessness, could be demonstrated in young Sabras following 3 min of shock which induced naloxone sensitive analgesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1985

Footshock-induced analgesia: neurochemical correlates and pharmacological profile.

The administration of electric shock to the feet of rats can produce either opioid, naloxone-sensitive analgesia or non-opioid, naloxone-insensitive analgesia. In our hands opioid analgesia could be elicited in young Sabra rats (75 days of age) by all analgesia induction methods while older rats of the same strain and rats of the Charles River-derived strain (CR) showed only naloxone-resistant analgesia. We therefore compared the effects of 2 different footshock parameters, 3 min continuous shock (3 mA) and 30 min intermittent shock (30 min, 1 s on 5 s off) on the responsiveness to noxious stimuli and on brain enkephalins and humoral (H-) endorphin content in these strains of rats. As previously reported, only young Sabra rats showed opioid analgesia whereas all other animals displayed naloxone-resistant effects. In contrast, no differential effects on brain opioids could be seen in these species. Thus, 30 min of shock produced a significant increase in brain enkephalins and a noticeable albeit non-significant increase in brain H-endorphin. A slight non-significant increase was seen following brief footshock. To assess the nature of non-opioid analgesia further we examined the effects of both reserpine and a series of antagonists on the analgesia produced by 3 and 30 min of either brief or prolonged shock. Pretreatment with reserpine caused a significant attenuation of non-opioid analgesia with both shock parameters while none of the antagonists administered (methysergide, phentolamine, phenoxybenzamine, yohimbine, theophylline, diphenhydramine and scopolamine) were effective.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1985

Footshock-induced analgesia: its opioid nature depends on the strain of rat.

Previous studies have indicated that stressful footshock can induce both opioid, naloxone-sensitive, and non-opioid, naloxone-insensitive forms of analgesia, depending on stimulation parameters used with 30 min of intermittent footshock (3 mA, 1 s on, 5 s off) producing opioid analgesia and 3 min of continuous shock (3 mA) producing non-opioid analgesia. Using a local strain of Charles River (CR)-derived rats we conducted a parametric investigation of footshock-induced analgesia applying both AC and DC scrambled shock ranging from 1 to 4 mA, continuous shock of 1, 3 and 5 min in duration and intermittent shock lasting 1, 3, 5, 10, 20, 30 and 80 min. All shock parameters produced potent analgesia. In no case did 10 mg/kg of naloxone block this analgesia. Varying the dose of the antagonist (0.1-10 mg/kg) and testing the animals at different points in the diurnal cycle did not result in the emergence of naloxone-sensitive anangesia. Based on the assumption that non-opioid systems may mask the activity of opioid analgesia systems, we attempted to either enhance opioid analgesia by: preventing enkephalin degradation by the use of D-phenylalanine; increasing the entry of blood-borne opioids into the brain by the use of DMSO; and the attenuation of non-opioid analgesia by the use of reserpine. In no case did a naloxone-sensitive component of analgesia emerge. To test whether the animals possess an intact opioid analgesia system, both electrical stimulation of, and injection of opiates into the periaqueductal gray (PAG) were examined. Both procedures produced analgesia which was reversed by naloxone.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesia↗

PubMed1985

Demonstration of endogenous "imipramine like" material in rat brain.

The extraction and partial purification of an endogenous "imipramine- like" material from rat brain is described. The endogenous factor obtained after gel filtration and silica chromatography inhibits [3H] imipramine specific binding and mimics the inhibitory effect of imipramine on [3H] serotonin uptake in both brain and platelet preparations. The effects of the endogenous material are dose-dependent and it inhibits [3H] imipramine binding in a competitive fashion. The factor is unevenly distributed in the brain with high concentration in the hypothalamus and low concentration in the cerebellum.

Animals↗