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F C Colpaert

Publications and source records attributed to F C Colpaert.

At least 19 recordsLinked to original sources
PubMed2003

Mutation in a protein kinase C phosphorylation site of the 5-HT1A receptor preferentially attenuates Ca2+ responses to partial as opposed to higher-efficacy 5-HT1A agonists.

The Thr(149)Ala mutation in a putative protein kinase C phosphorylation site of the 5-HT(1A) receptor's second intracellular loop has been shown to affect the closing of Ca(2+) channels and Ca(2+) mobilisation without interfering with the inhibitory cAMP pathway (Mol Pharmacol 52 (1997) 164). Here, the Ca(2+) responses for a series of 5-HT(1A) agonists were compared between the wild-type (wt) and mutant Thr(149)Ala 5-HT(1A) receptor as part of a fusion protein containing a G(alpha)(15) protein. Neither the mutation nor the fusion process modified the [(3)H]WAY 100635-based ligand binding profile of the fusion proteins as compared to the wt 5-HT(1A) receptor protein. Whereas at the wt 5-HT(1A) receptor, 5-HT induced a Ca(2+) response in CHO-K1 cells via endogenous G(i/o) proteins, the Ca(2+) response to 5-HT at the mutant Thr(149)Ala 5-HT(1A) receptor was fully dependent on either the co-expression or the fusion to a recombinant G(alpha)(15) protein. Buspirone, flesinoxan and 8-OH-DPAT produced a graded partial response (26 to 62%) at the wt 5-HT(1A):G(alpha)(15) fusion protein; F 13640, 5-CT and F 14679 behaved as higher-efficacy agonists with maximal Ca(2+) responses similar to 5-HT. The maximal Ca(2+) responses at the mutant Thr(149)Ala 5-HT(1A):G(alpha)(15) fusion protein were significantly attenuated for flesinoxan and 8-OH-DPAT (-45 and -36%, respectively); the response to the other 5-HT agonists was not significantly affected. A similar effect was observed upon treatment with phorbol 12-myristate 13-acetate at the Thr(149)Ala 5-HT(1A):G(alpha)(15) fusion protein. In conclusion, the amplitude of the Ca(2+) responses induced by partial, but not that to fuller 5-HT(1A) receptor agonists, is affected by the Thr(149)Ala mutation of the 5-HT(1A):G(alpha)(15) fusion protein.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2003

A persistent opioid-addiction state of memory.

We determined whether tolerance develops to a morphine-induced state of memory. Rats were injected with 5 mg/kg of morphine and trained to complete a FR-10 schedule of lever presses in daily sessions. The dose-response curve of morphine (1.25-40 mg/kg) in enabling retrieval was tested in one group immediately after criterion had been reached and, in another group, after an additional 40 training sessions. The additional training enhanced, rather than attenuated, the dependence of retrieval on morphine; this was because the further gain in response latency that developed during additional training also became state-dependent. Thus, because tolerance did not develop to the morphine state, an increasingly large body of engrams became encoded in that state, rendering retrieval increasingly dependent.

Animals↗
PubMed2003

Profound, non-opioid analgesia produced by the high-efficacy 5-HT(1A) agonist F 13640 in the formalin model of tonic nociceptive pain.

Previously, we have reported that in rat models of chronic pain, in particular, the very-high-efficacy 5-HT(1A) agonist F 13640 induces unprecedented pain relief by novel neuroadaptative mechanisms that involve inverse tolerance and cooperation with nociceptive stimulation in producing analgesia. The present studies detailed the actions of F 13640 and other compounds in the formalin model of tonic nociceptive pain. Intraperitoneal injection of F 13640 (0.01-2.5 mg/kg; t -15 min) caused a dose-dependent and complete inhibition of the paw elevation and paw licking that occurred both early (0-5 min) and late (22.5-27.5 min) after the intraplantar injection of diluted formaldehyde (2.5%) in the rat. The extent to which F 13640 and other 5-HT(1A) receptor ligands inhibited these pain behaviors correlated (p < 0.05) with the extent to which they activated 5-HT(1A) receptors. Under similar conditions, some inhibitory effects were also observed with various agents that are known to produce analgesia by different peripheral and/or central mechanisms (e.g., opioids, NA/5-HT reuptake inhibitors, COX-2 inhibitors and other nonsteroidal anti-inflammatory drugs, gabapentin, and ABT-594). However, with the possible exception of morphine, the effects of all of these agents at nontoxic doses were lower than those of F 13640, in particular in inhibition of early paw elevation. The 5-HT(1A) antagonist WAY 100635, but not naloxone, antagonized the actions of F 13640. These results help to establish large-magnitude 5-HT(1A) receptor activation as a new molecular mechanism of profound, central analgesia and suggest that F 13640 may be particularly effective against pain arising from severe tonic nociceptive stimulation.

Analgesics, Non-Narcotic↗
PubMed2002

Sign-reversal during persistent activation in mu-opioid signal transduction.

A concept of signal transduction in biological systems specifies that any instantaneous input is appreciated by its departure from the moving average of past activity. The concept provides an adequate account of the occurrence of both the one-directional (e.g. analgesic) effects induced by opioid receptor activation, and of the contra-directional (e.g. hyperalgesic) effects that can be observed when activation is discontinued. Following this transduction concept, the numerical simulations reported here revealed, remarkably, that under some parametric conditions, the input's effect may reverse even as input is maintained at a constant magnitude. In in vitro conditions that are proximal to the signal transduction that occurs when an opioid agonist binds to the G-protein coupled opioid receptor, the effects of opioid receptor activation were monitored by measuring time-dependent Ca(2+) responses in CHO-K1 cells transfected with a mu-opioid receptor and G(alpha 15) protein. The results indicate morphine to produce an initial increase in intracellular Ca(2+) concentration followed by a decrease below basal level. The occurrence of a sign-reversal was confirmed in native conditions of receptor-to-G protein coupling; the continuous in vivo infusion over a 2-week period of 0.31 mg rat(-1)day(-1) of fentanyl initially caused an increase of the mechanical threshold to induce a pain response (i.e. analgesia) that was followed by a decrease (i.e. hyperalgesia). The findings indicate that with opioid signaling systems, transduction mechanisms operate that may cause the sign of the effect to reverse not only when activation is discontinued but also whilst it is maintained at a constant magnitude.

Analysis of Variance↗
PubMed2002

Evidence for protean agonism of RX 831003 at alpha 2A-adrenoceptors by co-expression with different G alpha protein subunits.

Intrinsic properties of alpha(2) AR ligands were investigated by measuring two distinct signalling pathways via the alpha(2A) AR protein in CHO-K1 cells: (i) a Ca(2+) response mediated by a promiscuous G(alpha 15) protein; and (ii) a pertussis toxin-resistant [(35)S]GTP gamma S binding response mediated by a G(alpha o)Cys(351)Ile protein. The dexefaroxan analogue RX 831003 was virtually without intrinsic activity at the wt alpha(2A) AR via a G(alpha 15) protein, but induced a partial positive Ca(2+) response [pEC(50): 7.79 (0.17), E(max): 38+/-1% vs (-)-adrenaline] at the mutant Thr(373L)ys alpha(2A) AR. RX 831003 displayed a similar potency (pIC(50): 7.68 (0.21) for both the wt (E(max): -18+/-4%) and Thr(373)Lys alpha(2A) AR (E(max): -19+/-4%) inhibition of basal [(35)S]GTP gamma S binding via a G(alpha o)Cys(351)Ile protein. These data indicate that the alpha(2) AR ligand RX 831003 behaves as a protean agonist at the alpha(2A) AR and that its activity is highly dependent on the co-expressed G(alpha) protein subunit.

Adrenergic alpha-2 Receptor Agonists↗
PubMed2002

Large-amplitude 5-HT1A receptor activation: a new mechanism of profound, central analgesia.

We report the discovery of F 13640 and evidence suggesting this agent to produce powerful, broad-spectrum analgesia by novel molecular and neuroadaptative mechanisms. F 13640 stimulates G(alphaomicron) protein coupling to 5-HT(1A) receptors to an extent unprecedented by selective, non-native 5-HT(1A) ligands. Fifteen minutes after its injection in normal rats, F 13640 (0.01-2.5 mg/kg) decreases the vocalization threshold to paw pressure; 15 min upon injection in rats that are exposed to formalin-induced tonic nociception, F 13640 inhibits pain behavior. The initial hyperalgesia induced by 0.63 mg/kg F 13640 was followed, 8 hrs later, by paradoxical hypo-algesia; 5 mg/kg of morphine produces the opposite effects (i.e., hypo-algesia followed by hyper-algesia). Repeated F 13640 injections cause an increase in the basal vocalization threshold and a reduction of F 13640-produced hyperalgesia; in these conditions, morphine causes basal hyperalgesia and antinociceptive tolerance. Continuous two-week infusion of F 13640 (0.63 mg/day) exerts little effect on the threshold in normal rats, but markedly reduces analgesic self-administration in arthritic rats. F 13640 infusion also decreases allodynic responses to tactile and thermal stimulations in rats sustaining spinal cord or sciatic nerve injury. In these models of chronic nociceptive and neuropathic pain, the analgesia afforded by F 13640 consistently surpasses that of morphine (5 mg/day), imipramine (2.5 mg/day), ketamine (20 mg/day) and gabapentin (10 mg/day). Very-high-efficacy 5-HT(1A) receptor activation constitutes a novel mechanism of central analgesia that grows rather than decays with chronicity, that is amplified by nociceptive stimulation, and that may uniquely relieve persistent nociceptive and neuropathic pains.

Acetates↗
PubMed2002

Experimental conditions for the continuous subcutaneous infusion of four central analgesics in rats.

For the analysis of pharmacotherapeutic regimens for chronic pain in animals, it is important to establish delivery methods in which analgesics can be administered continuously and at a constant rate for a prolonged period of time. This allows for the assessment of how drug effects may vary over time in the presence of ongoing pain. The present study determined, for four analgesic compounds, the maximal doses that met all of the following criteria: (i) water-soluble, (ii) stable over 14 days at 38 degrees C, and (iii) devoid of undesirable side-effects in normal rats, as assessed by evolution of body weight and temperature after the subcutaneous implantation of an osmotic mini-pump that continuously infused the compounds over a 14-day period. The results showed the maximal doses to be 5 mg/rat/day for morphine hydrochloride, 2.5 mg/rat/day for imipramine hydrochloride, 20 mg/rat/day for ketamine hydrochloride, and 10 mg/rat/day for gabapentin. These doses were further found to be sufficient to express each compound's representative pharmacological activity. The conditions identified here appear appropriate for future studies of these four compounds in rat models of chronic pain and neuropathic allodynia.

Acetates↗
PubMed2001

Differential signalling of both wild-type and Thr(343)Arg dopamine D(2short) receptor by partial agonists in a G-protein-dependent manner.

G-protein activation and Ca(2+) responses by the wild-type D(2short) receptor and a mutation Thr(343)Arg, in the distal BBXXB motif of its third intracellular loop, were investigated in CHO-K1 cells in terms of ligand:receptor:G-protein interactions. No evidence was obtained for constitutive, agonist-independent receptor activation, but differences in the ligand-mediated activation profiles of both the wild-type and mutant Thr(343)Arg D(2short) receptor were observed. Most of the partial agonists, but not bromocriptine, displayed an enhanced response at the mutant D(2short) receptor, suggesting that the mutation brings the receptor in a more active state. This enhancement was apparent both at the level of G-protein activation ([35S]GTPgammaS binding) and at the effector (Ca(2+) response) and occurred with different G(alpha)-proteins. Partial agonists were also found to act differently via the wild-type D(2short) receptor depending on the involved G(alpha)-protein. Compared with higher efficacy agonists, partial agonists displayed Ca(2+) responses with slower and dissimilar kinetic properties. Lisuride and in particular bromocriptine produced a more potent response in the co-presence of a G(alphao) protein instead of a chimeric G(alphaq/o)- or a promiscuous G(alpha15)-protein. S(+)-propylnorapomorphine showed a similar partial response irrespective of the combined G(alpha)-protein. Bromerguride and (+)-UH 232 induced weak (16 to 21% versus dopamine) intrinsic activity in the co-presence of a G(alphaq/o)-protein in contrast to their silent properties with a G(alpha15)- or a G(alphao)Cys(351)Ile-protein. In conclusion, the present data strongly suggest that multiple activation binding sites are involved with these ligands at the D(2short) receptor, and that their activation may be unravelled by either the mutation or co-expressed G(alpha)-proteins being investigated.

Animals↗
PubMed2001

In the formalin model of tonic nociceptive pain, 8-OH-DPAT produces 5-HT1A receptor-mediated, behaviorally specific analgesia.

The experiments examined antinociceptive and intrinsic behavioral effects induced by the prototypical 5-HT1A receptor agonist 8-OH-DPAT (8-hydroxy-2-[di-n-propylamino] tetralin) in rats. 8-OH-DPAT (0.01-2.5 mg/kg, subcutaneous (s.c.)) reduced both the paw licking and paw elevation induced by (2.5%) formalin injection into the plantar surface of the right hindpaw; it also produced forepaw treading. All of these effects were completely blocked by pretreatment with WAY 100635 (N-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride) (0.16 mg/kg, s.c.); prazosin (0.63 mg/kg, s.c.) inhibited forepaw treading, but not 8-OH-DPAT's action on paw elevation and paw licking. Repeated injection of 8-OH-DPAT (0.63 mg/kg, s.c.) twice daily for 4 days, markedly reduced 8-OH-DPAT's ability to produce forepaw treading, but exerted only little and inconsistent effects on its paw licking and paw elevation-inhibiting action. The data indicate that 8-OH-DPAT exerts an analgesic action in the formalin model of tonic nociceptive pain; this action is mediated by 5-HT(1A) receptors, and is not confounded by the productive sign (i.e., forepaw treading) of the 5-HT syndrome which 8-OH-DPAT also induces.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2001

5-HT1A receptor activation and antidepressant-like effects: F 13714 has high efficacy and marked antidepressant potential.

To examine further the hypothesis that the magnitude of the intrinsic activity of agonists at 5-HT1A receptors determines the magnitude of their psychotropic activity, we studied the relationship between the maximal receptor activation produced by various 5-HT1A receptor ligands and their antidepressant-like effects (i.e., decreased immobility in the forced swimming test in rats). Using three different in vitro assays suitable to measure differences among high, intermediate, and low efficacy 5-HT1A receptor agonists, ligands were identified with intrinsic activities ranging from low-negative (i.e., the inverse agonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexane-carboxamide (WAY 100635)) to high-positive (i.e., 3-chloro-4-fluorophenyl-(4-fluoro-4-[[(5-methyl-6-methylamino-pyridin-2-ylmethyl)-amino]-methyl]-piperidin-1-yl-methanone (F 13714)). In addition, novel compounds with intermediate intrinsic activity, like buspirone, but with high selectivity for 5-HT1A receptors, unlike buspirone, were identified. The maximal effects of the 5-HT1A receptor ligands in the forced swimming test correlated positively (rS=0.91, P<0.005) with the rank order of their intrinsic activity at 5-HT1A receptors. This relationship constitutes evidence that the magnitude of the psychotropic activity of 5-HT1A receptor ligands is a positive function of their intrinsic activity at the receptor, and suggests that F 13714, which had maximal effects in the forced swimming test significantly larger than any of the other compounds examined here, did so because of its higher intrinsic activity at 5-HT1A receptors.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2001

Modulation of ligand responses by coupling of alpha(2A)-adrenoceptors to diverse G(alpha)-proteins.

The hypothesis that different signalling may be mediated via a single alpha(2A)-adrenoceptor (alpha(2A) AR) subtype was investigated by challenging alpha(2) AR ligands in combination with diverse recombinant wt, mutant, and chimeric G(alpha)-proteins. Possible coupling of alpha(2A) AR to endogenous G(alphai/o)-proteins in CHO-K1 cells was excluded by measuring pertussis toxin (PTX)-resistant [(35)S]GTPgammaS-binding responses as a common functional response to alpha(2A) AR activation. (-)-Adrenaline (10 microM) displayed the highest magnitude of [(35)S]GTPgammaS-binding response in the co-presence of a PTX-resistant G(alphao)Cys(351)Ile protein, whereas a decreased response was obtained with the mutant G(alphai1/2)-proteins. Replacement of the last six amino acids at the C-terminal portion of the G(alphao)-protein by the corresponding amino acid region of either the G(alphaz)-, G(alphas)-, G(alphaq)-, or G(alpha15)-protein and co-expression with the alpha(2A) AR resulted in similar maximal (-)-adrenaline-mediated [(35)S]GTPgammaS-binding responses with these chimeric G(alphao)-proteins. The ligands D-medetomidine, BHT 920 (6-allyl-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepin-2-ylamine) and (+)-RX 811059 (2-(2-ethoxy-2,3-dihydro-benzo[1,4]dioxin-2-yl)-4,5-dihydro-1H-imidazole) were weakly active or virtually inactive at the chimeric G(alphao/s)-, G(alphao/q)-, and G(alphao/15)-proteins in contrast to the G(alphao/z)-protein. Furthermore, combining the constitutively active mutant Thr(373)Lys alpha(2A) AR with these chimeric G(alphao)-proteins enhanced the apparent intrinsic activity of d-medetomidine and BHT 920. A similar observation was made using the corresponding fusion proteins, where the stoichiometry of the mutant alpha(2A) AR to the chimeric G(alphao)-protein was fixed at 1.0. These data indicate that a single ligand may display different magnitudes of activation at the alpha(2A) AR subtype coupled to chimeric G(alphao) proteins under controlled conditions of alpha(2A) AR: G(alphao)-protein expression.

Adrenergic alpha-Agonists↗
PubMed2001

Lack of toxic effects of F 12511, a novel potent inhibitor of acyl-coenzyme A: cholesterol O-acyltransferase, on human adrenocortical cells in culture.

Inhibition of acyl-coenzyme A: cholesterol O-acyltransferase (EC 2.3.1.26; ACAT) reduces intracellular cholesteryl esters that are substrates for steroidogenesis in adrenal cells. The adrenal side effects of ACAT inhibitors remain a key point for their development as antiatherosclerotic agents. The aim of this study was to characterize the effects of a novel and powerful ACAT inhibitor, F 12511 (S)-2',3',5'-trimethyl-4'-hydroxy-alpha-dodecylthio-phenylacetanilide, on the NCI-H295R cell line, which has functional properties comparable to those of normal human adrenal cells. F 12511 incubated with cultured cells for 4-72 hr strongly inhibited cholesteryl oleate formation. The concentrations required to produce 50% inhibition (IC50) values) ranged from 20 to 50 nM; in the presence of low-density lipoproteins (LDL), this effect was paralleled by a decrease in cholesteryl ester mass and an increase in intracellular free cholesterol. At concentrations 100-fold larger than the IC(50) value for up to 48 hr, F 12511 reduced neither the basal release of cortisol and aldosterone nor the production of cortisol stimulated by forskolin. F 12511 did not modify the mRNA levels of the steroidogenic enzyme genes cytochrome P450 cholesterol side-chain cleavage (P450scc), cytochrome P450 17alpha-hydroxylase (P450c17), or cytochrome P450 21-hydroxylase (P450c21) or those of the LDL receptor and high-density lipoprotein scavenger receptor class B, type I (SR-BI) genes, either in the presence or absence of adenosine 3',5'-cyclic monophosphate stimulation for 24 hr. Exposure to F 12511 at up to 3 microM for 24 or 48 hr did not result in significant change in morphological and ultrastructural characteristics; the cytoplasm contained large numbers of mitochondria with intact crystae, and the same typical features of secretory activity were observed in NCI-H295R control cells. Exposure to 3 microM of F 12511 for 96 hr also did not affect cell viability. These data demonstrate that reduction of the substrate for steroidogenesis by the ACAT inhibitor F 12511 impairs neither steroid production nor transcription of genes involved in steroidogenesis and lipoprotein uptake in the pluripotent human adrenal cell line NCI-H295R.

Adrenal Cortex Neoplasms↗
PubMed2001

Pharmacological profile of F 12511, (S)-2',3', 5'-trimethyl-4'-hydroxy-alpha-dodecylthioacetanilide a powerful and systemic acylcoenzyme A: cholesterol acyltransferase inhibitor.

The pharmacological profile of F 12511 (S)-2',3', 5'-trimethyl-4'-hydroxy-alpha-dodecylthio-phenylacetanilide, a new inhibitor of acyl-CoA: cholesterol acyltransferase (EC 2.3.1.26; ACAT), was evaluated by using different in vitro and in vivo models. In vitro, F 12511 was shown to be a highly potent inhibitor of ACAT activity in microsomal preparations from various animal species as well as of cholesterol esterification in relevant human cell lines in culture. The concentrations of F 12511 required to produce 50% inhibition of ACAT activity (IC(50) values) in microsomal preparations ranged from 41nM for hypercholesterolemic rabbit intestine to 223 nM for normocholesterolemic hamster liver. In whole cell assays using hepatic (Hep G2), intestinal (CaCo-2) and macrophagic (THP-1) cell lines, F 12511 inhibited ACAT activity with IC(50) values of 3, 7, and 71 nM, respectively. In vivo, orally administered F 12511 displayed high potency and efficacy as an antihypercholesterolemic compound in different cholesterol-fed animals (rat, guinea-pig, rabbit). For instance, in guinea-pigs the dose required to reduce plasma cholesterol levels by 30% (ED(30) value) was 0.008 mg.kg(-1.) In rabbits, an animal species prone to atherosclerosis, the hypocholesterolemic effect was accompanied by a dose-related reduction in the incidence of aortic fatty streaks that reached asymptote at 2.5 mg.kg(-1) and by an improvement of the impaired endothelial function. When given orally to chow-fed hamsters, F 12511 elicited a dose-related decrease in plasma cholesterol from 9% at 0.63 mg.kg(-1) up to 31% at 40 mg.kg(-1) associated with a preferential reduction in atherogenic lipoproteins, very low density lipoproteins (VLDL) and low density lipoproteins (LDL). Moreover, in the same dose range, F 12511 decreased hepatic cholesteryl ester concentrations and reduced liver ex vivo ACAT activity. By using a bioassay, ACAT inhibitory activity was present in plasma of treated hamsters 1 hr after oral administration of F 12511. Hence, the results in chow-fed hamsters are consistent with systemic and direct hepatic effects of F 12511. In guinea-pigs, an adreno-sensitive species, F 12511 did not impair the adrenal function (adrenocorticotrophic hormone challenge) at doses up to 2.5 mg.kg(-1,) far higher than those eliciting hypocholesterolemic effects in the same species. In conclusion, the results suggest that F 12511, a powerful and systemic ACAT inhibitor, constitutes an appropriate tool to determine whether the inhibition of ACAT constitutes an effective therapy for the treatment of hypercholesterolemia and of atherosclerosis in man.

Adrenal Glands↗
PubMed2001

Analysis of ligand activation of alpha 2-adrenoceptor subtypes under conditions of equal G alpha protein stoichiometry.

Variations in the measurement of ligand's intrinsic activity between receptor subtypes is a common consequence of unequal receptor:G protein density ratios. We have investigated ligand activation at the alpha2-adrenoceptor (alpha2-AR) subtypes under defined expression conditions of one receptor molecule for one Galpha protein molecule using fusion proteins. Fusion between either a wt alpha2C AR or a mutant Thr382Lys alpha2C AR and a chimeric Galphaq/il protein displayed robust, transient (-)-adrenaline-mediated Ca2+ responses with similar potencies (pEC50: 7.78 and 7.66) and kinetic properties. A comparison of the intrinsic activities of alpha2 AR agonists found d-medetomidine to be the only compound with an efficacy similar to that of (-)-adrenaline. The Ca2+ responses as mediated by UK 14304, oxymetazoline and clonidine became more potent and efficacious at the Thr381Lys alpha2C AR, whereas the response as mediated by talipexole displayed a higher potency with an unaltered maximal response. Whereas only small differences in ligand's intrinsic activities between the wt alpha2A, alpha2B and alpha2C AR fusion proteins were observed with most ligands, oxymetazoline was virtually silent at the alpha2A AR while active as a partial and apparently full agonist at the alpha2C AR and alpha2B AR, respectively. The mutant alpha2 AR subtypes could be differentiated using the apparent positive efficacy of ligands that used to be defined as antagonists. The following rank order of maximal responses was observed for the Thr381Lys alpha2C AR: idazoxan approximately equals SKF 86466 > atipamezole >> dexefaroxan; Thr373Lys alpha2A AR: SKF 86466 > idazoxan = atipamezole > dexefaroxan; and Thr370Lys alpha2B AR: atipamezole > idazoxan dexefaroxan. RX 811059 (10 microM) was the only compound to be completely silent at both the wt and mutant alpha2 AR subtypes. In conclusion, silent alpha2 AR ligands are probably rare in these specified alpha2 AR systems. Most antagonists may actually possess partial agonist properties at the alpha2 AR subtypes, which are facilitated by the same mutation in the distal portion of their third intracellular loop.

Adrenergic Agonists↗
PubMed2001

F 12511, a novel ACAT inhibitor, and atorvastatin regulate endogenous hypercholesterolemia in a synergistic manner in New Zealand rabbits fed a casein-enriched diet.

F 12511, a novel ACAT inhibitor, lowers plasma cholesterol levels in New Zealand rabbits fed a cholesterol-free casein-rich diet. In rabbits endogenous hypercholesterolemia pre-established for 8 weeks was used to compare treatments with F 12511 and atorvastatin for a further 8-week period, and to determine whether both agents act synergistically. F 12511 appears to be 3-4-fold more potent than atorvastatin in reducing total plasma cholesterol (active doses ranging from 0.16 to 2.5 and from 1.25 to 10 mg/kg per day, respectively) while the hypocholesterolemic efficacy of both compounds at 2.5 mg/kg per day amounted to 70 and 45%, respectively. A reduction by as much as 75% of esterified cholesterol in liver mediated by F 12511 could account for the decrease of plasma VLDL, LDL and apo B-100, whereas a reduction of the LDL production rate has been described as the main mechanism underlying the atorvastatin effect. F 12511 modified adrenal cholesterol balance only at the largest dose studied. In a further experiment the co-administration of threshold doses of F 12511 and atorvastatin (0.63 and 1.25 mg/kg per day, respectively) lowered plasma total cholesterol and apo B-100 containing lipoproteins to a greater extent and more rapidly than either agent alone. In the liver a decrease by atorvastatin in free cholesterol substrate for ACAT may amplify the effect of F 12511 on cholesteryl ester content leading to a diminution, in at least an additive manner, of the assembly and secretion of atherogenic lipoproteins in New Zealand rabbits which have developed an endogenous hypercholesterolemia. Thus, the combination of the ACAT inhibitor F 12511 with atorvastatin can represent a better approach than either agent alone to regulate lipoprotein metabolism in certain pathophysiological situations.

Adrenal Glands↗
PubMed2001

Modulation of 5-HT(1A) receptor activation by its interaction with wild-type and mutant g(alphai3) proteins.

Constitutive and agonist-dependent activation of the recombinant human 5-HT(1A) receptor (RC: 2.1.5HT.01A) was investigated by co-expression with a rat G(alphai3) protein in Cos-7 cells. The interaction between the 5-HT(1A) receptor and rat G(alphai3) protein was modulated by substitution of the G(alphai3) protein site for pertussis toxin-catalysed ADP-ribosylation (cysteine(351)) by each of the natural amino acids. Enhanced basal [(35)S]GTPgammaS binding responses (+24 to +189%) were observed with the mutant G(alphai3) proteins containing at position 351 either a histidine, glutamine, serine, tyrosine or a nonpolar amino acid with the exception of a proline. With each of these mutant G(alphai3) proteins, spiperone (10 microM), but not WAY 100635 (10 microM), reduced (-22 to -60%, p<0.05) the enhanced basal [(35)S]GTPgammaS binding response. 5-HT (10 microM)-mediated [(35)S]GTPgammaS binding responses attained for some of the mutant G(alphai3)Cys(351) proteins (Phe, Met, Val and Ala) more than 300% of that obtained with the wt G(alphai3) protein. Similar results were also obtained with the prototypical 5-HT(1A) agonist 8-OH-DPAT and the partial agonist (-)-pindolol. Fusion proteins assembled from the 5-HT(1A) receptor and either the wt G(alphai3)Cys(351), mutant G(alphai3)Cys(351)Gly or G(alphai3)Cys(351)Ile protein displayed similar observations for these ligands as obtained by co-expression of the 5-HT(1A) receptor with each of these G(alphai3) proteins. Both the degree of 5-HT(1A) receptor activation by 8-OH-DPAT and (-)-pindolol, and its inhibition by spiperone, strongly correlate (r(2): 0.78-0.81) with the octanol/water partition coefficients of the mutated amino acid at position 351 of the G(alphai3) protein. The present data also suggest the wt G(alphai3) protein does not result in maximal activation of the 5-HT(1A) receptor by the agonists being investigated.

Amino Acid Sequence↗
PubMed2001

Opiate self-administration as a measure of chronic nociceptive pain in arthritic rats.

The study examined the validity of oral fentanyl self-administration (FSA) as a measure of the chronic nociceptive pain that develops in rats with adjuvant arthritis independently of acute noxious challenges. Arthritic rats self-administered more of a 0.008 mg/ml fentanyl solution (up to 3.4 g/rat per day) than non-arthritic controls (0.5 g/rat per day) and did so with a biphasic time course that reached peak during weeks 3 and 4 after inoculation with Mycobacterium butyricum. The time course paralleled both the disease process and the chronic pain. Continuous infusion of dexamethasone during weeks 3 and 4 via subcutaneous osmotic pumps at 0.0025-0.04 mg/rat per day disrupted the arthritic disease and decreased FSA to a level (i.e. by 65%) similar to that observed in non-arthritic rats. Continuous naloxone (2.5 mg/rat per day) decreased FSA (by 55%) in arthritic but not in non-arthritic animals. Continuous, subcutaneous infusion of fentanyl also decreased arthritic FSA in a manner that varied with dose at 0.04-0.16 mg/rat per day doses, but leveled off at 47% of controls with 0.31 mg/rat per day. The effects of continuous fentanyl on arthritic FSA occurred only with those doses and dose-dependent dynamics with which fentanyl also induced dependence in non-arthritic rats. The findings indicate that pain, rather than the rewarding or dependence-inducing action of fentanyl mediates FSA in arthritic rats. Paralleling patient-controlled analgesic drug intake, FSA offers a specific measure allowing the dynamic effects of neurobiological agents to be studied in this unique animal model of persistent nociceptive pain.

Analgesics, Opioid↗