Intrastriatal dialysis evidence for a direct inhibitory effect of benztropine on dopamine re-uptake.

A direct inhibitory effect of benztropine on dopamine (DA) reuptake in the striatum was established by in vivo microdialysis of anesthetized rats. Benztropine was infused by means of a microdialysis probe positioned stereotaxically in the striatum. Extracellular DA collected from dialysate was measured by high-performance liquid chromatography using an electrochemical detector. Benztropine was found to cause a dose-dependent inhibition of re-uptake of DA in the nerve terminal area of the dopaminergic system.

Determination of succinylcholine hydrolytic enzyme activity in human plasma.

Succinylcholine is frequently employed in surgical procedures as a pre-anaesthetic. However, the lack of existing metabolic activity for this compound in some individuals entails a substantial risk. Normally, the risk is assessed indirectly through the measurement of pseudocholinesterase activity using other substrates, such as acetylcholine, rather than the agent itself. Thus, a method was devised to assess directly the hydrolysis of succinylcholine in human plasma samples. This method was applied to plasma samples derived from healthy men, healthy women, pregnant women and patients with silent pseudocholinesterasaemia.

Supersensitivity to electrical stimulation for assessing physical dependence on opioids in isolated tissues.

The use of the guinea pig ileum (GPI) and mouse vas deferens (MVD) to quantify opiate tolerance and physical dependence in the same preparation was examined. In the GPI, tolerance to and physical dependence on various opiates were induced by direct incubation with an agonist and tolerance and abstinence were assessed after its rapid removal by extensive washing. Dependence, as evidenced by an increase in twitch height and after removal of the agonist as compared to that before incubation, provided an index of the degree of physical dependence. The extent of the supersensitive response after agonist removal was noted to be related directly to the agonist concentration and the degree of tolerance development. Furthermore, the supersensitive response was found to be stereospecific, naloxone reversible and preferentially mu receptor-mediated. Likewise, tolerance to opiates could be demonstrated in the MVD by direct incubation with an agonist. Unlike the GPI, rapid removal of the agonist by washing did not produce a supersensitive response to electrical stimulation. However, a supersensitive response was demonstrable in the presence of naloxone. Thus, after a tolerant/dependent state was induced by incubation of the vas with a predetermined dose of [D-Ala2, D-Leu5]enkephalin that completely abolished the twitch response, the subsequent addition of naloxone resulted in a supersensitive response to electrical stimulation that was concentration-dependent. The maximum twitch response in the presence of naloxone, compared to that obtained before incubation with the agonist, provided an index of the extent of dependence.(ABSTRACT TRUNCATED AT 250 WORDS)

Proglumide exhibits delta opioid agonist properties.

Recently, it was reported that proglumide, a cholecystokinin (CCK) antagonist, potentiates the analgetic effects of morphine and endogenous opioid peptides and reverses morphine tolerance by antagonizing the CCK system in the central nervous system of the rat. In order to provide additional insight into the mode of action of this agent, we assessed the effect of proglumide in the isolated guinea pig ileum and the mouse, rat and rabbit vas deferens. Furthermore, we studied the in vitro binding affinity of this substance to mouse brain synaptosomes. Our results show that proglumide inhibits, dose dependently, the electrically stimulated twitches in the mouse vas deferens and guinea pig ileum, but not in the rat or rabbit vas deferens. The inhibitory action of proglumide on the mouse vas deferens, but not on the guinea pig ileum, is antagonized by naloxone and by the selective delta-antagonist, ICI 174,864, in a competitive fashion. Other CCK antagonists were found to be devoid of such activity on the mouse vas deferens. In vitro binding studies showed that proglumide displaces D-ala-D-[leucine]5-enkephalin (DADLE), a delta agonist, but not ethylketocyclazocine (EKC), a preferentially selective kappa agonist. The effect of proglumide appeared to be elicited presynaptically since it did not alter the norepinephrine-induced contractions of the mouse vas deferens. Our results suggest that proglumide might exert its opiate-like effects by activation of delta-opioid receptors.

Sites and mechanisms of basic narcotic receptor function based on current research.

Within the past decade, progress in opiate pharmacology has been phenomenal and has stimulated widespread interest. Several potent endogenous peptides with morphine-like activity were isolated and their structures were established. Opioid receptors in the brain were localized and characterized. Plausible hypotheses to explain the mechanism of action of the narcotic analgetics have been proposed. Antagonist-agonists that are potent analgesics with low addition liability were introduced for clinical application. Epidural administration of morphine and its surrogates to reduce side effects and prolong drug action is gaining increasing popularity. Extensive research is ongoing concerning the use of opioids in the treatment of shock and the mental states. Some of these advances will be discussed.

Stereospecific effect of naloxone hydrochloride on cyanide intoxication.

Cyanide intoxication in mice can be antagonized by the opiate antagonist, (-)naloxone HCl, alone or in combination with sodium thiosulfate and/or sodium nitrite. Potency ratios, derived from LD50 values, were compared in groups of mice pretreated with sodium nitrite (sc, 100 mg/kg), sodium thiosulfate (ip, 1 g/kg), and (-)naloxone HCl (sc, 10 mg/kg) either alone or in various combinations. These results indicate that naloxone HCl provides a significant protection against the lethal effects of potassium cyanide. The protective effect of sodium thiosulfate, but not sodium nitrite, was enhanced with (-)naloxone HCl. The combined administration of sodium nitrite and sodium thiosulfate was further enhanced with (-)naloxone HCl. This protective effect of naloxone HCl against the lethal effect of cyanide appears to be restricted to the (-)stereoisomer, as the (+)stereoisomer, the inactive opiate antagonist, is also inactive in protecting against the lethal effects of cyanide. The mechanism of antagonism is discussed.

Effects of morphine and B-endorphin on Ca2+-ATPase activity of synaptic plasma membranes.

Morphine and B-endorphin were found to inhibit the high calcium -affinity Ca2+-ATPase of synaptic plasma membranes which is believed to be involved in the regulation of intracellular Ca2+ that triggers the release of neurotransmitters. The inhibition was blocked by naloxone and reversed by calmodulin. Kinetic analyses revealed that opioids decreased the affinity of Ca2+-ATPase for Ca2+ and calcium bound to the enzyme decreased the affinity of the enzyme for opioids.

Comparative effects of dynorphin A(1-9) pyrrolidine analogs on isolated tissues.

Three dynorphin A(1-9) pyrrolidine analogs were synthesized by substituting isoleucine at position 8 with alanine (Ala), D-alanine (D-ala), and D-leucine (D-leu), and assayed for their effect on electrically induced twitches of the isolated guinea pig ileum and mouse vas deferens. All three dynorphin A(1-9) pyrrolidine analogs caused inhibition of the evoked twitches of the two preparations dose-dependently that was reversed by naloxone. However, the substitution by alanine or D-alanine resulted in a decrease in potency on guinea pig ileum when compared to dynorphin A(1-9) pyrrolidine and substitution by D-leucine caused a considerable loss of potency in both mouse vas deferens and guinea pig ileum. Although these substitutions reduced overall potency, a change of potency ratio towards more delta selectivity resulted.

Opioids and rat erythrocyte deformability.

In previous studies from this laboratory, it was noted that opioids in vitro reduced human red blood cell deformability. The effect was found to be dose-dependent, naloxone reversible and preferentially selective kappa ligands exhibited the highest potency. To extend these findings studies were carried out using rat erythrocytes. The time required for erythrocytes to pass through a 5.0 um pore membrane was determined and used as an index of deformability. Opioids added in vitro produced inhibition of deformability in a dose-dependent, naloxone reversible manner. Injecting naive animals with morphine or nalbuphine also produced dose related reductions in red cell deformability. The degree of inhibition produced by nalbuphine correlated well with its plasma concentrations as measured by high performance liquid chromatography (HPLC). Chronic morphine treatment by pellet implantation resulted in the development of tolerance as evidenced by a loss in the ability of morphine in vitro to inhibit red cell deformability. Addition of naloxone resulted in a decrease in filtration time. Thus, the data confirm and extend previous findings on human red blood cells. In as much as previous data from this laboratory demonstrated that opioids inhibit calcium flux from erythrocytes by inhibiting calcium-ATPase and calcium efflux is necessary for normal deformability, it is concluded that opioids act to reduce red cell deformability by inhibition of the calcium pump.

Inhibition of Ca++-ATPase of rat erythrocyte membranes by k-opioid agonists.

The effect of various opioid agonists on Ca++, Mg++-ATPase activity of rat erythrocyte membranes was studied. The Ca++-stimulated component of this enzyme (Ca++-ATPase) showed properties similar to those of the Ca++-pumping ATPase of human erythrocyte membranes, that is, high affinity for Ca++, potentiation by calmodulin, and insensitiveness to Na+. Ethylketocyclazocine (EKC) dose-dependently inhibited this Ca++-ATPase activity at a concentration less than one nM without changing basal Mg++-ATPase activity and this action was reversed by the antagonist Win 44,441. Other opioid agonists mimicked this EKC effect and the rank order of potency was dynorphin (1-13) = greater than EKC greater than levorphanol = morphine = B-endorphin = dihydromorphine greater than leu-enkephalin greater than (D-Ala)2-(D-leu)5-enkephalin (DADL) = morphiceptin. It is concluded that rat erythrocyte membranes possess k-type opioid receptors through which the Ca++-pump is inhibited.