Antagonism of metergoline on the diuretic effect of cyclazocine and U-50488 drugs with a kappa agonist activity.

In rats receiving a normal saline load of 2.5 ml/100 g, sc, (moderately hydrated rats), injections of the serotonin (5-HT) antagonist, metergoline (0.25-1-4 mg/kg), resulted in a dose-dependent decrease in the urine output induced by a dose of 8 mg/kg of cyclazocine (a benzomorphan derivative, mixed kappa and sigma agonist) at the 2-h time period. The antagonist effect of metergoline (1 mg/kg) on cyclazocine doses ranging from 0.25 to 8 mg/kg, was observed only at 2 mg/kg higher doses. Other 5-HT receptor blockers, methysergide, pizotifen, cyproheptadine, caused a significant degree of antagonism. In rats receiving a saline load and a water load of 5.5 ml/100 g, ip (hyperhydrated rats), metergoline (1 mg/kg) completely antagonized the diuretic effect of cyclazocine (8 mg/kg) at the 4-h and 5-h time periods. Similarly, metergoline (1 and 4 mg/kg) administered in moderately hydrated rats, markedly decreased at the 2-h time period, the urine output produced by 5 mg/kg of U-50488 (a non benzomorphan derivative, highly selective kappa agonist), and in hyperhydrated rats, completely suppressed, at the 4-h and 5-h time periods the drug-induced diuresis. Metergoline administered alone had no effect on urine output in moderately hydrated rats or in hyperhydrated rats. These results suggest the hypothesis that 5-HT may be involved in the complex mechanisms of kappa agonist-induced diuresis in rats.

[Protective effect of eptazocine, a novel analgesic, against cerebral hypoxia-anoxia in mice].

Cerebral protective effect of eptazocine, a mu-antagonist-kappa-agonist, was investigated using mice subjected to hypoxia-anoxia. Eptazocine (1 to 10 mg/kg) prolonged the survival time of mice subjected to KCN (3 mg/kg, i.v.) injection in a dose-dependent manner, and this effect was completely inhibited by naloxone (5 mg/kg). EKC, U50,488H, opioid kappa-agonists, also had such an effect, but were weaker than eptazocine. In mice exposed to hypobaric hypoxia (190 mmHg), eptazocine (3, 10 mg/kg) and EKC (10 mg/kg) prolonged the survival time, but morphine (5 mg/kg) and pentazocine (10 mg/kg) shortened the time. The eptazocine effect was attenuated by either naloxone (5 mg/kg) or atropine (0.5 mg/kg), different from what was seen in the case of physostigmine and diazepam, and the combination of eptazocine (1 mg/kg) and physostigmine (0.075 mg/kg) had a potentiating effect. MR-2266, a selective kappa-receptor antagonist, inhibited the eptazocine effect more potently than naloxone. These results suggest that eptazocine elicited its cerebral protective effect via its binding with opioid kappa-receptors and probably an activation of the central cholinergic system.

[Preferential action of eptazocine, a novel analgesic, with opioid receptors in isolated guinea pig ileum and mouse vas deferens preparations].

Actions of eptazocine, a novel analgesic, on isolated smooth muscle preparations were investigated. Eptazocine (10(-5) M) slightly inhibited electrically-driven twitch-tension in guinea pig ileum preparations sensitive to mu- and kappa-agonists, and this effect was antagonized by 10(-7) M naloxone. Eptazocine (10(-5)-10(-4) M) inhibited such an effect by the mu-agonist morphine. In mouse vas deferens preparations having delta-, mu- and kappa-receptors, eptazocine (10(-7) M-) inhibited the twitch-tension in a dose-dependent manner, being hardly inhibited by naloxone. On the other hand, MR-2266 (10(-6) M), a relatively selective kappa-receptor antagonist, inhibited the eptazocine effect. The Ke (equilibrium dissociation constant) value of naloxone against eptazocine was 325 nM and the Ke value of MR-2266 against eptazocine was 33.2 nM, showing that MR-2266 was 9.79-fold more effective than naloxone. These results suggest that eptazocine acted as a mu-receptor antagonist and as a kappa-receptor preferential agonist in isolated smooth muscle preparations.

[Influence of four opioids on pulmonary oxygenation and naloxone's effects in mechanically ventilated dogs].

In order to examine effects of opioids on pulmonary oxygenation during constant ventilation, we investigated changes in PaO2 following four different opioids and after reversal with naloxone in mechanically ventilated, lightly anesthetized dogs. The systemic administration of morphine 1.0mg.kg-1, buprenorphine 0.03mg.kg-1, butorphanol 0.1mg.kg-1, and cyclazocine 0.05mg.kg-1, did not affect PaO2, although these opioids decreased mean arterial pressure and heart rate significantly. Naloxone 0.04mg.kg-1 after four opioids affected the hemodynamics, significantly, but it did not cause any detrimental effects on pulmonary oxygenation. Although naloxone alone did not affect mean arterial pressure and heart rate at all, subsequent morphine decreased mean arterial pressure and heart rate significantly. Neither naloxone nor subsequent morphine produced any change in PaO2. The results suggest that reversal with naloxone may not cause any significant influences on pulmonary oxygenation in mechanically ventilated and anesthetized patients.

Antagonism of the analgesic effects of mu and kappa opioid agonists in the squirrel monkey.

The effects of several mu and kappa opioid agonists were examined alone and in combination with the opioid antagonist quadazocine in squirrel monkeys responding under a schedule of shock titration. Under this procedure, shock was scheduled to increase once every 15 sec from 0.01 to 2.0 mA in 30 steps. Five responses on a lever during the 15-sec shock period terminated the shock for 15 sec, after which the shock resumed at the next lower intensity. The intensity below which the monkeys maintained the shock 50% of the time (median shock level) and the rate of responding in the presence of shock were determined under control conditions and after administration of the mu agonists, l-methadone and fentanyl and the kappa agonists, bremazocine, ethylketocyclazocine, ketocyclazocine and U50,488. When examined alone, intermediate doses of mu and kappa agonists increased median shock level. At the highest doses of these compounds responding was eliminated and shock rose to its peak intensity. When the mu and kappa agonists were examined in combination with quadazocine, dose-effect curves for median shock level and for rate of responding were shifted to the right in a dose-dependent fashion. A comparison of the pA2 values for quadazocine on median shock level and on rate of responding revealed similar values for the two measures; however, pA2 values differed depending on the agonist examined. That is, the pA2 values for quadazocine in combination with l-methadone and fentanyl on median shock level were 7.43 and 7.61, respectively; whereas the pA2 value for quadazocine in combination with bremazocine and U50,488 were 6.53 and 6.43, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Only one pharmacophore is required for the kappa opioid antagonist selectivity of norbinaltorphimine.

We have investigated whether one or two pharmacophores are required for the kappa opioid receptor selectivity of the bivalent opioid antagonist norbinaltorphimine, (-)-1 (nor-BNI), by the synthesis and testing of its meso isomer 2. In smooth muscle preparations 2 was more potent than 1 and about half as selective as a kappa antagonist. Since 2 contains only one antagonist pharmacophore but yet retains substantial kappa selectivity, it is concluded that kappa selectivity is not dependent on the presence of two (-)-naltrexone-derived pharmacophores of 1. It is suggested that the kappa selectivity of (-)-1 and 2 is derived from the portions of the second halves of these molecules in that they mimic key "address" components of dynorphin at kappa opioid receptors.

Dissociation of the opioid and nonopioid effects of cyclazocine.

Lower IV doses of (dl)- and (l)-cyclazocine (0.05 and 0.50 mg/kg) in the rat produced opioid EEG and behavioral effects that were antagonized by naltrexone pretreatment. Higher IV doses of (dl)- and (l)-cyclazocine (1.00 and 2.00 mg/kg) produced initial "psychotomimetic-like" behavioral effects that were naltrexone-resistant, followed by the delayed emergence of opioid EEG and behavioral effects that were naltrexone-sensitive, (d)-Cyclazocine produced only "psychotomimetic-like" behavioral effects that were naltrexone-resistant. (dl)-Cyclazocine antagonized morphine-induced EEG and behavioral effects in naive rats. (l)-Cyclazocine precipitated withdrawal symptoms in morphine-dependent rats. In contrast, (d)-cyclazocine produced "psychotomimetic-like" effects, but no withdrawal symptoms. Thus, (dl)- and (l)-cyclazocine produced dose- and time-related opioid and nonopioid "psychotomimetic-like" effects, while (d)-cyclazocine produced only nonopioid "psychotomimetic-like" effects.

The topography of cholinergic transmission in the mechanism of drug action at muscarinic synapses of the guinea-pig ileum.

The pharmacology of cholinergic neurogenic responses evoked by the participation of only the endings of axon terminals was compared to that of responses evoked by participation of the more proximal parts of the terminals also. Myenteric plexus-longitudinal muscle strips of the guinea-pig ileum were drawn through narrow orifices in 2 rubber membranes dividing a bath into 3 separate compartments. Oral segments were stimulated electrically by single impulses or by trains and local neurogenic contractions were evoked. The contractions of the aboral segment due to nerve impulses transmitted from the oral segment via the middle segment were also recorded. The opioid ligands ketocyclazocine and [D-Ala2,MePhe4,Met(O)5-ol]enkephalin and noradrenaline inhibited the twitches of the aboral segment evoked by oral segment stimulation more than the local twitches of the oral segment when these agents were applied directly to the respective compartments. The twitches of the aboral segment were also inhibited by the application of these drugs into the middle compartment adjusted to 10 mm width. Verapamil and the alkaline earth metal ions cobalt and lanthanum had similar effects. 4-Aminopyridine increased twitch amplitude more in the aboral segment than in the oral segment when applied directly; similar effects in the aboral segment were seen when the agents were applied to the middle compartment. The action of atropine, papaverine, d-tubocurarine and prostigmine did not discriminate between twitches in the oral and aboral segment when applied directly and all drugs except prostigmine were without effect when applied to the middle compartment.(ABSTRACT TRUNCATED AT 250 WORDS)

Binaltorphimine and nor-binaltorphimine, potent and selective kappa-opioid receptor antagonists.

The opioid antagonist activities of two bivalent ligands, BNI and nor-BNI, have been evaluated in smooth muscle preparations and in mice. Both ligands are highly potent and selective as kappa opioid receptor antagonists, with relatively feeble blocking activity at mu and delta opioid receptors. BNI and nor-BNI represent the first highly selective kappa opioid receptor antagonists and should be of great utility as molecular probes for identifying the interaction of agonist ligands with kappa opioid receptors in vitro and in vivo.

Electrophysiological interactions of isomers of cyclazocine with the phencyclidine antagonist metaphit in rat cerebellar Purkinje neurons.

Metaphit, 1-(1-(3-isothiocyanatophenyl) cyclohexyl) piperidine, an analog of phencyclidine (PCP) has been shown previously to selectively block PCP receptors and to irreversibly antagonize the depressant effect of PCP in cerebellum. In this study, we examined the electrophysiological interactions of metaphit and naloxone with stereoisomers of cyclazocine, an agent known to have analgesic and psychotomimetic activity in behavioral studies, effects that have been ascribed to opiate and PCP receptor activity. A dose-dependent and reversible slowing of Purkinje neuron discharge was seen with local application of (+)- or (-)-cyclazocine. We found that the blockade of (-)-cyclazocine effects required both high doses of naloxone and the presence of metaphit, whereas the responses to (+)-cyclazocine were blocked by metaphit alone on most cerebellar Purkinje neurons. These findings suggest that the depressant reaction of (+)-cyclazocine in cerebellar Purkinje neurons is primarily mediated through PCP receptors. (-)-Cyclazocine responses, on the other hand, appear to be due to activity at both PCP and kappa opioid receptors.

Opiate-induced turning in rats after injection into the ventral tegmental area.

Morphine and ethylketazocine caused ipsilateral circling when injected unilaterally into the ventral tegmental area (VTA) of rats. Systemic naloxone only slightly inhibited this effect while systemic diprenorphine completely prevented circling. Systemic haloperidol and alpha-methyl-p-tyrosine also blocked circling. Rats made tolerant to morphine still turned after morphine injection into the VTA. Levorphanol, dextrorphan, methadone, DADLE, dynorphin(1-13), SKF 10,047 and phencyclidine were inactive when injected unilaterally into the VTA of naive rats; naloxone and naltrexone alone also were inactive. The opiate-induced circling appears to involve a non-mu opiate receptor as well as a dopaminergic neuronal system.

Mutual interaction between presynaptic alpha 2-adrenoceptors and opioid kappa-receptors at the noradrenergic axons of rabbit brain cortex.

The interaction between presynaptic, release-inhibiting alpha 2-adrenoceptors and opioid receptors was studied in slices of the parieto-occipital cortex of rabbits. The slices were preincubated with 3H-noradrenaline and then superfused with 3H-noradrenaline-free medium and stimulated electrically (3 or 7 Hz, 2 or 5 V/cm voltage drop between the electrodes). Clonidine and ethylketocyclazocine (EK) depressed, whereas yohimbine increased the electrically evoked overflow of tritium. When clonidine was administered first and retained in the medium for the rest of the experiment, the overflow-inhibiting effect of EK was reduced. When yohimbine was administered first and kept for the rest of the experiment, the effect of EK was enhanced. When, finally, EK was administered first and clonidine as the second drug, the overflow-inhibiting effect of clonidine was attenuated. The changes in the effect of EK (by clonidine or yohimbine) and clonidine (by EK) were not due to the changes in release per se produced by the drugs that were given first. Naloxone shifted the concentration-response curve of EK to the right; the dissociation constant of the naloxone-receptor complex, calculated from the shift, was 13 nmol/l. It is concluded that there is an interaction between presynaptic alpha 2-adrenoceptors and opioid kappa-receptors, either at the level of the receptors themselves or of the post-receptor reaction chains. Activation of one kind of receptor blunts the inhibition of release produced by activation of the other kind of receptor.

Reversal by beta-funaltrexamine of the antinociceptive effect of opioid agonists in the rat.

The effect of the irreversible opioid receptor antagonist, beta-funaltrexamine (beta-FNA), on antinociception produced by mu- and kappa-receptor agonists was studied in the rat. beta-FNA, 20 to 80 mg kg-1, s.c., given 24 h before testing, produced a dose-related antagonism of the effects of morphine in the paw pressure, hotplate and tail-flick tests. Following the 80 mg kg-1 dose, the degree of antagonism of morphine was stable for up to 48 h after dosing, but was reduced by 5 days and had disappeared by 8 days. In the paw pressure test, beta-FNA, 40 mg kg-1, s.c., antagonized the effects of fentanyl, buprenorphine, tifluadom, ethylketocyclazocine and proxorphan; it was without effect against the highly selective kappa-agonist, U-50,488. In light of these results, the possible opioid receptor selectivities of both the agonists and beta-FNA are reassessed.

Differentiating opioids by their pupillary effects in the rat.

Pupillary effects of several opioids were examined as part of a broader in vivo study of multiple opioid receptors in the rat. Agonist activity, stereospecificity, and naloxone sensitivity were determined by methadone (Me), ethylketocyclazocine (EK), and N-allylnormetazocine (SKF 10,047), selected for their purportedly predominant actions at mu, kappa, and sigma receptors, respectively. After an acute, subcutaneous injection of each drug, pupil area and fluctuations in pupil size were measured by means of an infrared video pupillometer on line with a microcomputer data processing and storage system. Despite differences in the magnitude of the response, each opioid tested produced an increase in pupil size which was stereospecific, independent of behavioral responses to the drugs and, for 1-Me and 1-SKF 10,047, dose-related. Other differences among the opioids were found in their ability to induce fluctuations (1-Me and 1-EK) and a pendular nystagmus (1-SKF 10,047 only), and in their sensitivity to naloxone. Although 1.0 mg/kg naloxone completely reversed 1-Me-induced mydriasis, 10 mg/kg was needed to reverse 1-EK, and this dose only partially antagonized 1-SKF 10,047. These characteristic patterns of pupillary responses to opioids in terms of agonist activities and naloxone sensitivities indicate that the different opioid receptor types subserve different functions with respect to pupillary control.

Electrophysiological effects of cyclazocine on rat cerebellar Purkinje neurons: comparison with phencyclidine.

Cyclazocine is a benzomorphan which, in addition to more classical opiate properties, binds to the sigma opiate receptor site. Recently, it has been suggested that the sigma opiate receptor is identical to the binding site responsible for the actions of phencyclidine (PCP). Since the electrophysiological actions of PCP have already been demonstrated on rat cerebellar Purkinje neurons, the effects of cyclazocine were also studied in this system with the goal of comparing the electrophysiological effects of cyclazocine to those of PCP. Cyclazocine inhibited the spontaneous firing rates of Purkinje neurons. These responses were stereospecific and qualitatively appeared similar to the effects of PCP. Antipsychotic drugs, haloperidol and fluphenazine, partially antagonized the actions of cyclazocine, suggesting a catecholaminergic involvement similar to the mechanism proposed for PCP. Unlike PCP, the effects of cyclazocine were also partially reversed by the opiate antagonist, naloxone. Taken together, these results suggest that in the rat cerebellum cyclazocine may be interacting with at least two receptor mechanisms: a naloxone-sensitive opiate site, and a naloxone-insensitive site which might involve catecholaminergic mediation similar to the PCP mechanism of action. The naloxone-sensitive effects of cyclazocine, however, may be related to an interaction of the drug with kappa receptors rather than with the more classical mu or delta opiate mechanisms.

Comparative antagonism by naltrexone and naloxone of mu, kappa, and delta agonists.

In the guinea pig ileum preparation, naltrexone was 3.5 to 5 times more potent than naloxone in antagonizing morphine but the antagonists were equipotent in antagonizing ethylketazocine. In the mouse vas deferens preparation, naltrexone and naloxone were equipotent in antagonizing both morphine and [D-Ala2-D-Leu5]enkephalin. The data provide evidence that the naltrexone-reversible mu population of receptors in the guinea pig ileum are different from those in the mouse vas deferens. These findings also point out the uniqueness of the mu receptor system in the guinea pig ileum which is reflected by the potency differences between naltrexone and naloxone.

Antagonism of the discriminative effects of ethylketazocine, cyclazocine, and nalorphine in macaques.

dl-Ethylketazocine (EKC, 0.01 mg/kg) and saline were established as discriminative stimuli for food-maintained responding in macaque monkeys. Thirty consecutive presses on a right or left lever were reinforced with food, contingent on whether EKC or saline were administered before the session. For tests of antagonism, naltrexone, or UM 979 [(l)-5,9-alpha-dimethyl-2-(3-furylmethyl)-2'-hydroxy-6,7-benzomorphan] was administered concomitantly with EKC, dl-cyclazocine, or nalorphine. Both antagonists blocked completely the EKC discriminative stimulus. The antagonism of the stimulus and rate-altering effects of EKC was surmountable, with considerable intersubject variability in the magnitude of the EKC dose increase required to overcome the blockade. Cyclazocine and nalorphine, mixed agonist-antagonist opioids that share stimulus properties with EKC, were also susceptible to antagonism. Naltrexone antagonized completely the EKC stimulus effects of nalorphine; naltrexone and UM 979 antagonized completely the EKC stimulus effects of cyclazocine. Naltrexone antagonism of the cyclazocine stimulus was not surmountable, due to a lack of antagonism of the rate-decreasing effects of high cyclazocine doses.

[Pharmacological actions of eptazocine (l-1,4-dimethyl-10-hydroxy-2,3,4,5,6,7-hexahydro-1,6-methano-1,H-4-benzazonine). 4. Antagonistic action of naloxone on eptazocine analgesia].

It was investigated whether the analgesic effects of eptazocine were antagonized by treatment with naloxone, one of the opiate antagonists, and whether morphine-induced effects were affected by eptazocine. The analgesic effects of eptazocine, similar to those of morphine, were completely antagonized by treatment with 0.5 mg/kg naloxone, s.c., as determined by the hot plate and pressure methods in mice and by the tail-flick method in rats. In contrast, as tested by the acetic acid-induced writhing method in mice, the analgesic effect of eptazocine, similar to that of pentazocine, was not antagonized by treatment with 1.0 mg/kg naloxone, s.c., while that of morphine was antagonized by 0.5 mg/kg naloxone, s.c. Using the acetic acid-induced writhing method in mice, the pA2 values of naloxone were found to be the following order: eptazocine less than pentazocine less than morphine. In addition, the analgesic effect of morphine was dose-dependently antagonized by the treatment with eptazocine as determined by the pressure method. Furthermore, the stimulating effect of morphine on spontaneous locomotor activity was also antagonized by eptazocine. These results suggest that eptazocine may be classified as one of the opiate agonist-antagonists.

Potency of three opiate antagonists to reverse the inhibitory activity of dynorphin, enkephalins and opioid-like alkaloids on the guinea pig ileum.

To test the hypothesis that dynorphin is a K-opiate agonist acting on the myenteric plexus, the potency of two benzomorphan antagonists (Win 44, 441 and Mr 2266) to block the inhibitory action of dynorphin, enkephalins and opioid alkaloids was determined on the longitudinal muscle preparation of the guinea pig ileum. The effectiveness of these antagonists was compared to that of naloxone. Antagonistic potency was established by calculating the apparent antagonist dissociation constant, Ke, as derived from Schild plots. Win 44, 441 and Mr 2266 were about 7-8 times more potent than naloxone against dynorphin, dynorphin-(1-13) or ethylketocyclazocine. Although the Ke obtained with Win 44, 441 or Mr 2266 against dynorphin or ethylketocyclazocine were significantly lower than those of naloxone, the values obtained for these antagonists did not differ significantly in the case of each of these agonists. With respect to the antagonism of the enkephalins or normorphine, Win 44, 441 was the most potent antagonist. Its Ke value for the enkephalins was 2.5-3 times lower than those for dynorphin or ethylketocyclazocine and in comparison to naloxone, Win 44, 441 was about 5 times more potent. Although Mr 2266 was a potent antagonist of dynorphin, ethylketocyclazocine, the enkephalins or normorphine, it showed no selectivity of action. The fact that the 3 opiate antagonists evidenced similar Ke values for dynorphin and ethylketocyclazocine, but different ones for the enkephalins or normorphine supports the conclusion that dynorphin activates preferentially K- but not mu-opiate receptors in the myenteric plexus.