British journal of pharmacology
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1. DFU (5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)phenyl-2(5H)-furan one) was identified as a novel orally active and highly selective cyclo-oxygenase-2 (COX-2) inhibitor. 2. In CHO cells stably transfected with human COX isozymes, DFU inhibited the arachidonic acid-dependent production of prostaglandin E2 (PGE2) with at least a 1,000 fold selectivity for COX-2 (IC50 = 41 +/- 14 nM) over COX-1 (IC50 > 50 microM). ⋯ The results indicate that COX-1 inhibitory effects can be detected for all selective COX-2 inhibitors tested by use of a sensitive assay at low substrate concentration. The novel inhibitor DFU shows the lowest inhibitory potency against COX-1, a consistent high selectivity of inhibition of COX-2 over COX-1 (>300 fold) with enzyme, whole cell and whole blood assays, with no detectable loss of integrity of the gastrointestinal tract at doses >200 fold higher than efficacious doses in models of inflammation, pyresis and hyperalgesia. These results provide further evidence that prostanoids derived from COX-1 activity are not important in acute inflammatory responses and that a high therapeutic index of anti-inflammatory effect to gastropathy can be achieved with a selective COX-2 inhibitor.
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1. Population synaptic responses of motoneurones were recorded from a ventral root following electrical stimulation of the corresponding lumbar dorsal root in neonatal rat hemisected spinal cord preparations in vitro. Two levels of electrical stimulation were used to elicit dorsal root compound action potentials that contained either an A fibre component alone or both A and C fibre components. ⋯ CGP40116 (3 microM) depressed the high intensity e.p.s.p. to 62 +/- 8%, the low intensity e.p.s.p. to 22 +/- 4% and the train e.p.s.p. to 16 +/- 2% of control values. 5. The depressant actions of morphine were fully reversed by naloxone (1 microM) and those of clonidine were fully reversed by atipamezole (1 microM). 6. These results show that, in contrast to previous findings, activation of primary afferent C fibres in dorsal roots is not required for generation of morphine- or clonidine-sensitive synaptic responses in ventral roots of this in vitro preparation.
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1. The GABA modulating and GABA-mimetic actions of the general anaesthetic etomidate were examined in voltage-clamp recordings performed on Xenopus laevis oocytes induced, by cRNA injection, to express human recombinant gamma-aminobutyric acidA (GABAA) receptor subunits. 2. Currents mediated by recombinant receptors with the ternary subunit composition alpha x beta y gamma 2L (where x = 1,2,3 or 6 and y = 1 or 2), in response to GABA applied at the appropriate EC10, were enhanced by etomidate in a manner that was dependent upon the identity of both the alpha and beta subunit isoforms. 3. ⋯ The nature of the alpha-subunit also impacts upon the maximal potentiation and activation that the compound may elicit. Such pronounced influences may aid the identification of the site that recognises etomidate. More generally, these results provide a clear example of structural specificity in anaesthetic action.
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Comparative Study
Differential influence of D1 and D2 dopamine receptors on acute opiate withdrawal in guinea-pig isolated ileum.
1. The effects exerted by D1 and D2 dopamine agonists and antagonists on the acute opiate withdrawal induced by mu- and kappa-receptor agonists were investigated in vitro. 2. Following a 4 min in vitro exposure to morphine (moderately selective mu-agonist), [D-Ala2, Me-Phe4, Gly-ol5]enkephalin (DAMGO, highly selective mu-agonist) or U-50488H (highly selective kappa-agonist) the guinea-pig isolated ileum exhibited a strong contracture after the addition of naloxone. 3. ⋯ Bromocriptine, a D2 selective dopamine receptor agonist was able to increase significantly, and in a concentration-dependent manner, the naloxone-induced contracture by mu- and kappa-opioid agonists, whereas SKF 38393, a D1 selective dopamine receptor agonist, increased only the withdrawal after morphine or U50-488H. 6. Our data indicate that both D1 and D2 dopamine agonists and antagonists are able to influence opiate withdrawal in vitro, suggesting an important functional interaction between the dopaminergic system and opioid withdrawal at both the mu- and kappa-receptor level. 7. Furthermore, the ability of sulpiride to block strongly opiate withdrawal when compared to SCH 23390, as well as the effect of bromocriptine to increase opiate withdrawal suggest that D2 dopamine receptors may be primarily involved in the control of opiate withdrawal.
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1. Radioligand binding and patch-clamp techniques were used to study the actions of gamma-aminobutyric acid (GABA) and the general anaesthetics propofol (2,6-diisopropylphenol), pentobarbitone and 5 alpha-pregnan-3 alpha-ol-20-one on rat alpha 1 and beta 3 GABAA receptor subunits, expressed either alone or in combination. 2. Membranes from HEK293 cells after transfection with alpha 1 cDNA did not bind significant levels of [35S]-tert-butyl bicyclophosphorothionate ([35S]-TBPS) (< 0.03 pmol mg-1 protein). ⋯ By contrast, this phenomenon was not apparent following applications of 5 alpha-pregnan-3 alpha-ol-20-one (10 microM) to cells expressing alpha 1 beta 3 receptors. 9. These observations demonstrate that rat beta 3 subunits form homomeric receptors that are not spontaneously active, are insensitive to GABA and can be activated by some general anaesthetics. Taken together, these data also suggest similar sites on GABAA receptors for propofol and barbiturates, and a separate site for the anaesthetic steroids.