[Inhibitory effect of bithionol on NADH-fumarate reductase in ascarides].

To elucidate the mechanism of anthelmintic action of bithionol, the inhibitory effect of the drug on NADH-fumarate reductase (NADH-FR) of Ascaris lumbricoides suum was examined. NADH-FR, an enzyme of anaerobic carbohydrate metabolic pathway was solubilized from the mitochondria of the worm's muscle with deoxycholate, and then partially purified with the monoethanolamine-Sepharose 4B column chromatography. Rhodoquinone (RQ), which is required for the electron transfer from NADH to fumarate, was separated from the enzyme protein and phospholipids. Although the enzyme protein fraction eluted from the above column did not show NADH-FR activity, this enzyme was reactivated by the addition of purified RQ and phosphatidylcholine. The IC50 value of bithionol for reconstituted NADH-FR was 18 +/- 2 microM. The inhibition type was competitive to RQ. Bithionol inhibited at most 30% NADH-ferricyanide reductase, which did not require RQ, even at high concentration of 150 microM. These results suggest that the pharmacological action of bithionol, a phenolic anthelmintic, depends on the inhibition of the electron transport system by the competition with RQ.

Inhibitory effects of NaCl and guanyl-5'yl-imidodiphosphate (GppNHp) on [3H]naloxone binding to kappa-opioid receptors in guinea pig cerebellum.

Studies were performed to characterize the opioid receptors in guinea pig brain using the radiolabeled opioid antagonists, [3H]naloxone and [3H]diprenorphine and the kappa-agonist [3H]U-69593. The binding of [3H]U-69593 to guinea pig cerebellar membranes was reduced by NaCl, guanyl-5'yl-imidodiphosphate (GppNHp) and NaCl+GppNHp, and [3H]naloxone binding to cerebellar membranes was also reduced by NaCl and GppNHp. In the guinea pig cerebral cortex and striatum and the rat cerebellum, [3H]naloxone binding was not affected significantly by GppNHp in the presence or absence of 100 nM [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO) and [D-Ala2, D-Leu5]enkephalin (DADLE). Guinea pig cerebellar [3H]diprenorphine binding was not affected by NaCl, GppNHp or NaCl+GppNHp. Furthermore, [3H]naloxone binding was reduced after pretreating cerebellar membranes with N-ethylmaleimide (NEM), which also attenuated GppNHp-induced inhibition of cerebellar [3H]naloxone binding. These results suggest that the properties of [3H]naloxone binding in guinea pig cerebellum differ from those in other brain regions and rat cerebellum, and that the interaction of [3H]naloxone and [3H]U-69593, but not [3H]diprenorphine, with guinea pig cerebellar opioid receptors is associated with a G-protein.

Contractile response of guinea pig ileum by repetitive application of morphine.

1. The repetitive application of morphine gradually induced a contracture in the isolated guinea pig ileum. 2. The optimum conditions for induction of the contracture were as follows: the concentration, incubation time and washout time of morphine were 1 or 10 microM, 2 and 3 min, respectively. 3. Preincubation with naloxone or TTX blocked this morphine-induced contracture. 4. Among twitch-inhibiting drugs, only clonidine induced a contracture similar to that induced by morphine, while tetrodotoxin (TTX) and adenosine did not. 5. The contracture was also observed in the longitudinal muscle-myenteric plexus preparations. 6. These findings indicate that morphine has a dual inhibitory and excitatory action on the guinea pig ileum and that its repetitive application preferentially diminish the inhibitory one.

Characterization of antagonistic activity and binding properties of SR 95531, a pyridazinyl-GABA derivative, in rat brain and cultured cerebellar neuronal cells.

Experiments were performed to characterize the antagonistic activity and binding properties of SR 95531 [2-(3' carbethoxy-2'-propyl)-3-amino-6-paramethoxy-phenyl-piridazinium bromide] in rat brain. SR 95531 and bicuculline methiodide inhibited muscimol-stimulated 36Cl- uptake in cortical synaptoneurosomes in a concentration-dependent manner. The inhibitory potency of SR 95531 for the muscimol-stimulated 36Cl- uptake was 15 times higher than that of bicuculline methiodide. Scatchard plots of binding isotherms exhibited two apparent binding sites for [3H]SR 95531 in both the frontal cortex and cerebellum. The IC50 value of SR 95531 for muscimol-stimulated 36Cl- uptake into cortical synaptoneurosomes was in close agreement with the KD value of low-affinity binding sites of [3H]SR 95531 in the frontal cortex. Pretreatment of the membranes with phospholipase A2 invariably decreased [3H]SR 95531 binding in the frontal cortex and cerebellum. On the other hand, the treatment significantly increased [3H]gamma-aminobutyric acid (GABA) binding in a concentration-dependent manner in the frontal cortex. Although lower concentrations of phospholipase A2 did not affect [3H]GABA binding in the cerebellum, treatment with higher concentrations of phospholipase A2 increased the binding in this region. Specific binding of [3H]SR 95531 was also detected in cultures rich in cerebellar granule cells. Pretreatment with phospholipase A2 affected the binding of [3H]GABA and [3H]SR 95531 in these cells, as in the case of the cerebellum. These effects of phospholipase A2 on the binding of [3H]GABA and [3H]SR 95531 were partially prevented by the addition of delipidated bovine serum albumin.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of bicuculline on [3H]SR 95531 binding in discrete regions of rat brains.

Effects of bicuculline in vitro, and acute and chronic treatment of a subconvulsive dose of bicuculline on [3H]SR 95531 binding to discrete regions of rat brains were studied in Sprague-Dawley rats. Scatchard analysis of the binding isotherms exhibited two populations of binding sites for [3H]SR 95531 in frontal cortex, cerebellum, striatum and substantia nigra. The apparent KD for high-affinity sites was significantly increased in the frontal cortex and cerebellum in the presence of bicuculline (1 microM) with no change in Bmax. In contrast, the apparent affinity for low-affinity sites was not altered in the presence of bicuculline in these regions, whereas the Bmax was significantly decreased in the cerebellum. Following acute (2 mg/kg, i.p.) or chronic (2 mg/kg, i.p. for 10 days) bicuculline treatment, [3H]SR 95531 binding was also investigated in various regions of brains. The acute bicuculline treatment did not affect the [3H]SR 95531 binding in any of the regions studied. In contrast, apparent affinity for [3H]SR 95531 was significantly decreased in low-affinity sites of all regions studied in rats treated chronically with bicuculline. The Bmax values of high and low-affinity sites were significantly increased in the cerebellum with no change in the frontal cortex, striatum and substantia nigra. The present study demonstrates that chronic bicuculline treatment decreases apparent affinity of [3H]SR 95531 binding whereas the treatment increases apparent affinity of [3H]muscimol binding (1) in various brain regions. The results indicate that significant increase in Bmax of [3H]SR 95531 and [3H]muscimol binding in the cerebellum may be due to true up-regulation of GABA binding sites, involving increased de novo synthesis of receptor protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Withdrawal like responses of rat hippocampal slices following brief exposure to morphine.

An acutely acquired dependence was investigated in rat hippocampal slices after brief exposure to morphine. Morphine augmented the population spike amplitude. Naloxone not only reversed the augmentation but decreased the amplitude to a level below that of the control. The inhibitory effect of naloxone correlated with the period of preincubation with morphine. These results suggested that the decreased response may indicate the withdrawal state acquired in vitro.

Assay and disposition of carvedilol enantiomers in humans and monkeys: evidence of stereoselective presystemic metabolism.

Carvedilol is a new beta-blocking agent with vasodilating activities, which is a racemic mixture of R(+)- and S(-)-enantiomers. Since the two enantiomers differ in pharmacological properties, it is necessary to individually measure their plasma concentrations in order to evaluate the pharmacological effects of racemic carvedilol after oral administration. In this study, a sensitive, stereospecific high-performance liquid chromatographic assay was used to determine the plasma concentration of each enantiomer. The assay involves the diastereomeric derivatization of racemic carvedilol with 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate as a chiral reagent. After oral administration of racemic carvedilol to humans, the mean Cmax and AUC infinity values for R(+)-enantiomer were 2.6 and 2.8 times greater, respectively, than those for the more active S(-)-enantiomer. Similarly, in monkeys, the respective R:S enantiomer ratios for Cmax and AUC infinity were 1.5 and 1.2. The difference in AUCoral between these enantiomers is ascribed to the greater intrinsic clearance of S(-)-enantiomer than that of the R(+)-enantiomer in the liver, and to a lower plasma protein binding of the S(-)-enantiomer.

Induction of cytochrome P-450c and P-450d by metyrapone in the primary culture of rat hepatocytes.

The effects of metyrapone on qualitative changes in cytochrome P-450-dependent drug metabolizing activities in primary cultures of rat hepatocytes were investigated. Metyrapone apparently increased benzo(a)pyrene hydroxylation and maintained both ethoxycoumarin-O-deethylation and propoxycoumarin-O-depropylation, whereas it had little effect on methoxycoumarin-O-demethylation. Furthermore, P-450d (high spin type of P-448) as well as P-450c (low spin type of P-448) were induced by metyrapone, while P-450b and P-450e were not. In conclusion, metyrapone act as a 3-methylcholanthrene-like inducer in the primary cultures of rat hepatocytes.

Kappa-opioid agonists do not inhibit adenylate cyclase.

Morphine, levorphanol and D-Ala2, Met enkephalin, but not bremazocine, pentazocine, U-50 488H and U-69 593, were found to inhibit adenylate cyclase activity dose-dependently in bullfrog brain membranes. The inhibition of the enzyme activity was abolished by naloxone. These results suggest that the signalling transduction of mu- and delta-agonists is partially mediated by the adenylate cyclase system coupled with opioid receptors, but that kappa-receptors may not be associated with adenylate cyclase.

[Characterization of opioid receptor from bullfrog brain].

Among the tested five species--carp, bullfrog chicken, rat, and mouse--the solubilized fraction derived from the bullfrog brain gave the highest binding activity similar to that of membranes. The difference in their binding activities was demonstrated to depend on the Bmax value, but not on Kd. High-affinity binding of [3H]naloxone and [3H]ethylketocyclazocine (EKC) was proved in supernatant of detergent-treated membranes. The displacement curves of various [3H]ligands binding to the membrane and solubilized fraction by a series of agonists suggested that kappa-receptors are rich in the bullfrog brain. Guanyl-5'yl-imidodiphosphate (GppNHp) and N-ethylmaleimide (NEM) reduced the proportion of opioid receptors with a high affinity for mu-agonist, because the high-affinity states of opioid receptors were converted to the low-affinity states by GppNHp and NEM. The degree in shift of these displacement curves of [3H]naloxone binding by above agonist in bullfrog brain membranes, was slight when compared with that of the rat brain membranes. GppNHp slightly affected the displacement curves of [3H]naloxone binding caused by levorphanol or delta-receptor peptide, but the displacement curve for bremazocine was not affected by GppNHp, suggesting that participation of GTP binding protein is minor in kappa-receptor of the bullfrog.

Inhibitory mechanism of opioid binding to receptor by phospholipase A2.

1. The inhibition of [3H]naloxone binding to the opioid receptor upon short-term incubation with phospholipase A2 (Plase A2) was abolished by treatment with BSA, but not after long-term incubation. 2. In contrast to the restorative effect of BSA on the strong inhibition occurring with Plase A2, BSA only partially abolished the inhibitory effect of arachidonic acid or lysophosphatides, even though the degree of inhibition was slight. 3. These results suggest that Plase A2 products only become associated with hydrophobic receptor sites or with phospholipids near to the receptor, thus reversibly inhibiting opioid binding, and that irreversible inhibition occurs through release of the phospholipid necessary for receptor binding.

Some properties of brain opioid receptors in membrane bound and solubilized state.

In brain membrane preparations, 3H-naloxone binding to bullfrog brain gave the highest values versus other species such as carp, chicken, rat and mouse. Scatchard analysis revealed that the Bmax value of bullfrog brain membranes was three fold greater than that of rat brain membranes. Opioid receptors were solubilized from bullfrog brain membranes using digitonin or 3-(cholamidopropyl)-dimethylammonio-1-propane sulfonate (CHAPS) as the detergent. The properties of solubilized opioid receptors were essentially the same as membrane bound receptors with regard to sensitivity to various treatments. The order of potency for a series of agonists in displacing 3H-naloxone binding in both membrane and solubilized preparations was bremazocine greater than pentazocine greater than morphine greater than delta-receptor peptide. Partial purification of opioid receptors was performed using a fast protein liquid chromatography system. Specific binding activity of 3H-naloxone was increased 10-15 fold within 20 min using the Mono Q column.