Changes in multifidus and abdominal muscle size in response to microgravity: possible implications for low back pain research.

PURPOSE: In microgravity, muscle atrophy occurs in the intrinsic muscles of the spine, with changes also observed in the abdominal muscles. Exercises are undertaken on the International Space Station and on Earth following space flight to remediate these effects. Similar effects have been seen on Earth in prolonged bed rest studies and in people with low back pain (LBP). The aim of this case report was to examine the effects of microgravity, exercise in microgravity and post-flight rehabilitation on the size of the multifidus and antero-lateral abdominal muscles. METHODS: Ultrasound imaging was used to assess size of the multifidus, transversus abdominis and internal oblique muscles at four time points: pre-flight and after daily rehabilitation on day one (R + 1), day 8 (R + 8) and day 14 (R + 14) after return to Earth (following 6 months in microgravity). RESULTS: Exercises in microgravity maintained multifidus size at L2-L4, however, after spaceflight, size of the multifidus muscle at L5 was reduced, size of the internal oblique muscle was increased and size of transversus abdominis was reduced. Rehabilitation post-space flight resulted in hypertrophy of the multifidus muscle to pre-mission size at the L5 vertebral level and restoration of antero-lateral abdominal muscle size. CONCLUSIONS: Exercise in space can prevent loss of spinal intrinsic muscle size. For the multifidus muscles, effectiveness varied at different levels of the spine. Post-mission rehabilitation targeting specific motor control restored muscle balance between the antero-lateral abdominal and multifidus muscles, similar to results from intervention trials for people with LBP. A limitation of the current investigation is that only one astronaut was studied, however, the microgravity model could be valuable as predictable effects on trunk muscles can be induced and interventions evaluated. Level of Evidence Case series.

Granulomatous peritoneal disease associated with oxaliplatin-based chemotherapy for ampullary adenocarcinoma: a case report.

Adenocarcinomas of the ampulla of Vater represent only 0.2% of all gastrointestinal cancers. Due to the low incidence no large clinical trials evaluating efficacy of treatments are available. Adjuvant therapy is often administered in patients with stage IB or higher. Oxaliplatin is considered as an effective and well tolerated therapeutic option. Adverse events associated with this therapy include cardio-, neuro-, nephrotoxicity and myelosuppression. Previously granulomatous pulmonary and liver manifestations have been described in oxaliplatin-based chemotherapy. In this report peritoneal manifestation of granulomatous disease associated with oxaliplatin is described for the first time. Sarcoidlike reactions may be misinterpreted as tumour progression or metastatic disease, and may consequently result in over-treatment.

A survey among Flemish gastroenterologists about endoscopic sedation practices in colorectal cancer screening.

Background & study aims: The sedation levels and methods used for colonoscopy in colorectal cancer screening programs vary from country to country and from continent to continent. Little is known in the literature about how frequently the different sedation levels are used in colorectal cancer screening colonoscopies. We made a survey among all Flemish gastroenterologists (GI) to determine how frequently they use the different sedation modalities in this target population and to determine the motives of the GI to opt for one or another sedation modality. Patient and methods: An online survey was sent to all 329 Flemish GI by e-mail. A reminder e-mail was sent one month later. Participants could indicate how frequently (by percentage) they used the different sedation methods (no sedation, minimal sedation, conscious sedation, deep sedation) and which sedative medication they administered. In addition, they were asked to indicate their main motives for choosing a specific sedation method. Descriptive statistics were used. Results: 112 out of 329 GI answered the questionnaire (response rate 34%). Anesthesia monitored care is the most frequently used sedation modality, followed by conscious sedation. Patient preference is the main motive for most GI to use each sedation modality. Conclusions: Anesthesia monitored care is currently the most frequently used sedation regimen to perform a colonoscopy in the FIT positive population or in the colorectal cancer screening program in Flanders. The motives given by the GI for choosing one or another sedation modality are not always congruent with current scientific evidence or guidelines.

Efficacy of switching to infliximab in patients with Crohn's disease with loss of response to adalimumab.

BACKGROUND AND STUDY AIMS: Anti-TNF monoclonal antibodies are a cornerstone in the treatment of Crohn's disease. Prospective data on switching from the subcutaneous and human adalimumab (ADM) to the intravenous and chimeric infliximab (IFX) are scarce. PATIENTS AND METHODS: In this prospective, observational, multicentre cohort study we included 21 patients with loss of response to ADM despite at least 4 consecutive weekly injections. Clinical response (CDAI drop≥70 points) and remission (CDAI≤150) were assessed after switching from ADM to IFX after 10 weeks, 6 and 12 months. Predictive factors of response/remission, the need for therapy intensification, discontinuation and safety were investigated. RESULTS: Short-term response and remission (10 weeks) were seen in 57% and 48% respectively. Mid- and long-term clinical response and remission were achieved in 40% and 25% after 6 months and in 45% and 20% after 12 months respectively. At 12 months, 81% still were on IFX. IFX therapy intensification was needed in half of the patients at 6 months and three quarter of patients at 12 months. Undetectable ADM trough levels (despite weekly injections) were a predictive factor for short-term response and remission to IFX. About half of the patients with response at week 10 maintained response at 6 and 12 months. CONCLUSIONS: Switching from ADM to IFX can be efficacious in patients with loss of response, in particular in case of undetectable ADM trough levels. The majority of patients however will need IFX therapy intensification during their first year of treatment.

Pharmacology of hexahydro-difenidol, hexahydro-sila-difenidol and related selective muscarinic antagonists.

A series of hexahydro-difenidol (HHD) and hexahydro-sila-difenidol (HHSiD) analogues modified in the amino group, the phenyl ring and in the alkylene chain were investigated for their binding and functional properties at muscarinic M1, M2 and M3 receptors. Novel muscarinic receptor antagonists were obtained which exhibited different receptor selectivity profiles from the parent compounds HHD and HHSiD (M1 congruent to M3 greater than M2), e.g. HHD and HHSiD methiodides, M1 greater than M2 congruent to M3; p-fluoro-HHSiD, M3 greater than M1 greater than M2; trans-hexbutenol, M1 greater than M3 greater than M2; and (s)-p-fluoro-hexbutinol, M3 greater than M2 congruent to M1. Stereoselectivity ratios [(R)/(S)] for the enantiomers of HHD, hexbutinol and p-fluoro-hexbutinol were highest at M1, intermediate at M3 and lowest at M2 receptors.

Stereoselectivity of the interaction of muscarinic antagonists with their receptors.

The stereoselectivity of the interaction with muscarinic receptors of enantiomers of a series of chiral antagonists is receptor subtype dependent. There is no overall relationship between stereoselectivity and receptor affinity. Depending on the antagonist studied, receptor stereoselectivity may indeed reflect: (1) the weakening or loss of a single interaction involving one of the four groups bound to the asymmetric carbon; (2) steric hindrance preventing optimum interaction of the low affinity steroisomer with the receptor; and/or (3) the inversion of the relative positions of two moieties of the ligand with similar structural and electronic properties i.e. comparable affinities for the two corresponding subsites in the receptor.

Antagonistic properties of the suramin analogue NF023 at heterologously expressed P2X receptors.

The suramin analogue 8,8'-(carbonylbis(imino-3,1-phenylene carbonylimino)bis(1,3,5-naphthalenetrisulfonic acid) (NF023) antagonizes in a competitive fashion P2X receptor-mediated responses in certain vascular and visceral smooth muscles. In the present study, the effect of NF023 on voltage-clamped Xenopus oocytes heterologously expressing homomultimeric P2X1-P2X4 as well as heteromultimeric P2X2/P2X3 receptors has been characterized. P2X1 receptors were most sensitive to inhibition by NF023 with IC50 values of 0.24 and 0.21 microM for the rat and human homologue, respectively. P2X3 receptors have an intermediate sensitivity with IC50 values of 8.5 and 28.9 microM for rat and human subtypes, respectively and P2X2 was the least sensitive subtype (IC50 > 50 microM). P2X4 receptors were insensitive to NF023 at concentrations up to 100 microM. Coexpression of rat P2X3 with rat P2X2 resulted in receptors whose sensitivity to NF023 was identical to that obtained for homomultimeric rat P2X3 receptors (alphabeta meATP as agonist; IC50 = 1.4 and 1.6 microM, respectively). NF023 inhibited P2X1 receptors in a voltage-insensitive manner. In addition, NF023 (5 and 30 microM) caused a shift of the concentration-response curve to the right without affecting the maximal response to ATP (K(B) = 1.1 +/- 0.2 microM). Our results indicate that NF023 is a subtype-selective and surmountable antagonist at P2X1 receptors heterologously expressed in Xenopus oocytes.

The suramin analogue NF279 is a novel and potent antagonist selective for the P2X(1) receptor.

The suramin analogue 8,8'-(carbonylbis(imino-4, 1-phenylenecarbonylimino-4,1-phenylenecarbonylimino)) bis(1,3,5-naphthalenetrisul fonic acid) (NF279) was analysed with respect to its potency and P2X receptor subtype selectivity. Two-electrode voltage-clamp measurements were performed with Xenopus laevis oocytes expressing homomultimeric rat P2X(1), P2X(2), P2X(3) and human P2X(4) receptors. For the fast desensitising P2X(1) and P2X(3) receptors, IC(50) values strongly depended on whether oocytes were pre-incubated with NF279 prior to ATP superfusion or exposed to NF279 simultaneously with ATP. With a 10 s pre-incubation period of NF279, IC(50) values of 19 nM and 1.62 microM were obtained for rat P2X(1) and P2X(3), respectively. Without pre-incubation, IC(50) values amounted to 2 microM and 85.5 microM for P2X(1) and P2X(3), respectively. For the non-desensitising rat P2X(2) receptor NF279 appeared to act as a competitive antagonist with an IC(50) value of 0.76 microM and a K(B) value of 0.36 microM, as derived from Schild analysis. P2X(4) receptors were the least sensitive subtypes for NF279 (IC(50)>300 microM). The antagonism was fully reversible at all P2X subtypes analysed. Our results indicate that NF279 is a potent P2X(1) receptor-selective and reversible antagonist.

Muscarinic ganglionic stimulants: conformationally restrained analogues related to [4-[[N-(3-chlorophenyl)carbamoyl]oxy]-2-butynyl]trimethylammonium chloride.

The synthesis of a series of tertiary and quaternary cyclic analogues (isoarecolinol, dihydroisoarecolinol, arecolinol, and 3-pyrroline-3-carbinol derivatives) of [4-[[N-(3-chlorophenyl)carbamoyl]oxy]-2-butynyl]trimethylammonium chloride (McN-A-343) (1), a selective stimulant of muscarinic receptors in sympathetic ganglia (so-called M1 receptors), is reported. The compounds 3-10 were tested for muscarinic ganglion-stimulating activity by recording blood pressure responses in pithed rats. All tertiary compounds tested had no ganglion-stimulating activity. Among the series of quaternary derivatives, only the isoarecolinol analogues 4a and 4b showed considerable ganglion-stimulating effects, whereas the dihydroisoarecolinol (8), the arecolinol (6a, 6b), and the 3-pyrroline-3-carbinol derivatives (10) were much less potent. Our experiments therefore demonstrate that in this series a quaternary nitrogen atom, unsaturation at C2 of the ammonium side chain, and a certain spatial arrangement of the ammonium and the phenylcarbamate groups are essential for potent M1-receptor stimulating activity.

Kadsurenone distinguishes between different platelet activating factor receptor subtypes on macrophages and polymorphonuclear leucocytes.

The effects of the antagonist kadsurenone on the platelet activating factor (Paf)-induced chemiluminescence of guinea-pig peritoneal macrophages and on pig peripheral blood leucocyte aggregation were compared. Linearity and slopes of unity of the Schild plots confirmed the competitive nature of the antagonism by kadsurenone. pA2 values indicated a 91 fold lower affinity of kadsurenone for leucocyte Paf receptors than for those in macrophages. It is concluded that these two types of Paf receptors are not identical and are provisionally designated Paf1 and Paf2 receptors, respectively.

Functional role of muscarinic M(2) receptors in alpha,beta-methylene ATP induced, neurogenic contractions in guinea-pig ileum.

1. The muscarinic acetylcholine receptors mediating the contractile response elicited to endogenous acetylcholine released by the selective P2X receptor agonist alpha,beta-methylene ATP (mATP) were investigated in guinea-pig ileum. 2. mATP (0.1 - 30 microM) elicited a concentration-dependent neurogenic contractile response inhibited by tetrodotoxin (TTX) and antagonized by the non-selective muscarinic receptor antagonist N-methylscopolamine (NMS). 3. The contractile response to mATP was pertussis toxin-insensitive, irreversibly antagonized by N-(2-chloroethyl)-4-piperidinyl diphenylacetate (4-DAMP mustard), and unaffected by the muscarinic M(2)/M(4) receptor selective antagonist AF-DX 116 (1 microM). 4. When measured in the presence of histamine and isoproterenol after treatment with 4-DAMP mustard, mATP elicited a pertussis toxin-sensitive contractile response potently antagonized by AF-DX 116. 5. Collectively, our data suggest that endogenous acetylcholine released by mATP can elicit a direct contractile response through the muscarinic M(3) receptor and an indirect contractile response through the muscarinic M(2) receptor by antagonizing the relaxant effects of isoproterenol on histamine induced contraction.

Antagonism of platelet activating factor-induced chemiluminescence in guinea-pig peritoneal macrophages in differing states of activation.

1. The effects of the platelet activating factor (Paf) antagonists alprazolam, BN 52021, kadsurenone, L 652,731 and SRI 63119 have been studied on Paf-induced chemiluminescence (CL) of guinea-pig, C. parvum-activated peritoneal macrophages in vitro. 2. All antagonists produced a shift to the right in the dose-response curve to Paf (0.001-10 mumol l-1). Schild plots for BN 52021, L 652,731, kadsurenone and SRI 63119 were linear, but only for BN 52021 and kadsurenone did the mean slope not differ significantly from unity. Mean pA2 values for BN 52021 and kadsurenone were 6.60 +/- 0.05 and 6.41 +/- 0.14 (mean + s.e.mean) respectively. Calculation of IC50 values for all antagonists (at 0.1 mumol l-1 Paf) gave an order of potency: L 652731 greater than kadsurenone greater than or equal to BN 52021 greater than alprazolam greater than SRI 63119. 3. When individual pA2 values for BN 52021 and kadsurenone were plotted against the maximal CL response to Paf of cell suspensions in the absence of antagonist (reflecting the degree of activation of the macrophages by the C. parvum), it was found that the affinity of both antagonists for macrophage Paf receptors remained relatively constant irrespective of the activation state of the cells. 4. We conclude that activation of guinea-pig peritoneal macrophages does not account for the increased affinity for macrophage Paf receptors previously observed for kadsurenone. Kadsurenone and BN 52021 presumably bind to a site on Paf receptors which is not affected by the activation process, while alprazolam and SRI 63119 are non-specific antagonists. The reason for the difference between the competitive nature of kadsurenone and its structural analogue L 652,731 is unclear.

Selectivity profile of the novel muscarinic antagonist UH-AH 37 determined by the use of cloned receptors and isolated tissue preparations.

1. Functional in vitro experiments were carried out to determine the antimuscarinic potencies of the pirenzepine derivative UH-AH 37 (6-chloro-5,10-dihydro-5-[(1-methyl-4-piperidinyl)acetyl]-11H-dibenzo- [b,e] [1,4] diazepine-11-one hydrochloride) at M1 muscarinic receptors of rabbit vas deferens, M2 receptors of rat left atria and M3 receptors of rat ileum. Furthermore, N-[3H]-methylscopolamine competition binding experiments were performed to obtain its affinities for the five cloned human muscarinic receptors (m1-m5) stably expressed in CHO-K1 cells. Pirenzepine served as a reference drug throughout all experiments. 2. In all preparations used, UH-AH 37 interacted with muscarinic receptors in a fashion characteristic of a simple competitive antagonist. 3. In the functional studies, UH-AH 37, like pirenzepine, showed high affinity for M1 (pA2 8.49) and low affinity for M2 muscarinic receptors (pA2 6.63). In contrast to pirenzepine, UH-AH 37 also displayed high affinity for M3 receptors (pA2 8.04). 4. In agreement with its functional profile, UH-AH 37 bound with highest affinity to m1 (pKi 8.74) and with lowest affinity to m2 receptors (pKi 7.35). Moreover, it showed a 7 fold higher affinity for m3 (pKi 8.19) than for m2 receptors, whereas pirenzepine bound to both receptors with low affinities. 5. The binding affinity of UH-AH 37 for m4 and m5 receptors (pKi 8.32 for both receptors) was only ca. 2.5 fold lower than that for m1 receptors, while the corresponding affinity differences were 6 and 13 fold in case of pirenzepine. 6. In conclusion, the receptor selectivity profile of UH-AH 37 differs clearly from that of its parent compound, pirenzepine, in both functional and radioligand binding studies, the major characteristics being its pronounced M2 (m2)/M3 (m3) selectivity. UH-AH 37 thus represents a useful tool for the further pharmacological characterization of muscarinic receptor subtypes.

Structure-activity relationships of new analogues of arecaidine propargyl ester at muscarinic M1 and M2 receptor subtypes.

1. The potency of arecaidine propargyl ester (APE) and of several analogues containing a modified ester side chain has been assessed at M1 and M2 muscarinic receptor subtypes. APE was shown to act as a potent agonist at ganglionic M1 receptors in the pithed rat, at M2 receptors in guinea-pig isolated atria (-log EC50 = 8.22) and ileum (-log EC50 = 7.77). 2. The arecaidine 2-butynyl and 2-pentynyl esters were approximately equipotent with APE at M1 and M2 receptors, whereas the 2-hexynyl derivative was found to be less potent than APE in atria (-log EC50 = 6.80) and ileum (-log EC50 = 6.70) by about one order of magnitude. The 2-heptynyl and 3-phenyl propargyl esters exhibited no agonist actions in atria and ileum. 3. Shifting the triple bond from the 2 to the 3 position and introducing a bulky group at position 1 of the ester side chain of APE and analogues resulted in competitive antagonists (pA2 ranging from 4.9 to 7.3). 4. APE and its 2-butynyl analogue showed some agonistic selectivity for cardiac M2 receptors (potency ratio, ileum/atria = 2.8 and 4.6 respectively). All antagonists in this series of compounds were not selective in terms of affinity since their pA2 values at cardiac and ileal M2 receptors were similar (potency ratios, ileum/atria = 0.4 to 1.2).

Selective antagonism by PPADS at P2X-purinoceptors in rabbit isolated blood vessels.

1. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), a P2-purinoceptor antagonist, was investigated for its ability to antagonize: (1) P2X-purinoceptor-mediated contractions of the rabbit central ear artery and saphenous artery evoked by either alpha,beta-methylene ATP (alpha,beta-MeATP) or electrical field stimulation (EFS); (2) P2Y-purinoceptor-mediated relaxations of the rabbit mesenteric artery; (3) endothelium-dependent and endothelium-independent, P2Y-purinoceptor-mediated relaxations of the rabbit aorta. 2. alpha,beta-MeATP (0.1-100 microM) caused concentration-dependent contractions of the rabbit ear and saphenous arteries. The negative log[alpha,beta-MeATP] that produced a contraction equivalent to the EC25 for noradrenaline (ear artery) or histamine (saphenous artery) in the absence of PPADS was 6.60 +/- 0.18 (9) and 6.18 +/- 0.17 (9) in the ear artery and saphenous artery, respectively. These effects of exogenous alpha,beta-MeATP were concentration-dependently inhibited by PPADS (1-30 microM). In the ear artery, the negative log[alpha,beta-MeATP] producing a contractile response equivalent to the EC25 of noradrenaline, in the presence of PPADS at 1, 3 and 10 microM was 6.16 +/- 0.18 (8), 5.90 +/- 0.18 (8) and 4.72 +/- 0.36 (8), respectively (P < 0.01). In the saphenous artery, the negative log[alpha,beta-MeATP] values equivalent to the EC25 for histamine in the presence of PPADS at concentrations of 1, 3, 10 and 30 microM were 5.90 +/- 0.19 (8), 5.73 +/- 0.16 (8), 4.99 +/- 0.14 (8) and 4.51 +/- 0.13 (8), respectively (P < 0.01). 3. PPADS at a concentration of 1 microM had no effect on contractions of the ear artery evoked by EFS (4-64 Hz; 1 microM phentolamine present). At higher concentrations (3-30 MicroM) it caused concentration dependent inhibition of neurogenic contractions. In the saphenous artery, PPADS (1-30 MicroM) concentration-dependently inhibited contractions evoked by EFS at frequencies of 4, 8 and 16 Hz. Contractions evoked by EFS at frequencies of 32 and 64 Hz were significantly inhibited by PPADS only at concentrations of 10 and 30 MicroM.4. PPADS (30 MicroM) had no effect on relaxations to 2-methylthio ATP (3 nM-3 MicroM) in rabbit mesenteric artery and to ATP (1 MicroM-I mM) in rabbit aorta (with endothelium intact or removed). In addition,PPADS (30 MicroM) had no significant influence on the contractile potency of noradrenaline and histamine in rabbit ear and saphenous artery, respectively.5. In conclusion, these results support the evidence that PPADS is a selective antagonist of P2X-purinoceptor-mediated responses.

Investigation of the actions of PPADS, a novel P2x-purinoceptor antagonist, in the guinea-pig isolated vas deferens.

1. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) was investigated for its ability to act as an antagonist at P2x-purinoceptors which mediate neurogenic excitatory junction potentials (e.j.ps) and contractions in the guinea-pig isolated vas deferens. 2. PPADS (10(-7) M) caused a small potentiation of the phasic, predominantly purinergic component of contractions evoked by symapthetic nerve stimulation, but higher concentrations of PPADS (3 x 10(-6)-3 x 10(-5) M) elicited a substantial and significant concentration-dependent inhibition. In contrast, over the same concentration-range, PPADS had no effect on the tonic, predominantly noradrenergic phase. 3 PPADS (3 x 10(-5) M) also inhibited contractile responses to exogenous alpha,beta-methyleneATP (10(-8)-10(-3)M), a P2x-purinoceptor agonist, without affecting the responses to exogenous noradrenaline (10(-8)-10(-3) M), carbachol (10(-5) M) or histamine (10(-4) M). 4. PPADS (10(-7)-3 x 10(-5) M) produced a concentration-dependent reduction in e.j.p. magnitude and resting membrane potential. The maximum effect was seen at 10(-5) M PPADS, which reduced e.j.p. magnitude from 13.7 +/- 0.6 mV (n = 12) to 1.8 +/- 0.7 mV (n = 12) and membrane potential from -64.8 +/- 0.6 mV (n = 51) to -55.0 +/- 1.8 mV (n = 12). 5. The PPADS-induced depolarization was not inhibited by the P2x-purinoceptor antagonist, suramin (10(-4) M). This indicates that the depolarization was not due to an agonist action of PPADS at P2x-purinoceptors. 6. The results support the proposal that PPADS is a selective antagonist at P2x purinoceptors as opposed to non-P2-purinoceptors in the guinea-pig vas deferens, but its ability to cause membrane depolarization independently of P2x-purinoceptors and also, at a low concentration, to potentiate the phasic component of the neurogenic contraction indicates that it has other actions.

Stereoselective recognition of the enantiomers of phenglutarimide and of six related compounds by four muscarinic receptor subtypes.

1. We have compared the binding properties of the enantiomers of phenglutarimide (1) and of six related compounds to M1 receptors in NB-OK-1 cells, M2 receptors in rat heart, M3 receptors in rat pancreas and the M4 receptors of rat striatum, with their functional (antimuscarinic) properties in rabbit vas deferens (M1/M4-like), guinea-pig atria (M2) and guinea-pig ileum (M3) receptors. The binding properties of the enantiomers of three of the compounds were also measured on cloned human m1-m4 receptors expressed by CHO cells, using [3H]-N-methylscopolamine ([3H]-NMS) as radioligand. 2. The high affinity enantiomers behaved as competitive antagonists in binding and pharmacological studies. (S)-phenglutarimide (pKi-M1 = 9.0/9.3) and (R)-thienglutarimide (pKi-M1 = 8.6/9.2) recognized selectively the native M1 > M4 > M3 > M2 receptors in tissues as well as the respective cloned receptors. 3. The pA2 values at the inhibitory heteroreceptors in the rabbit vas deferens, and at the guinea-pig atria and ileum for the seven more potent enantiomers were compatible with the previous classification of these receptors as M1/M4-like, M2 and M3, respectively. 4. Replacement of the phenyl by a thienyl ring or of the diethylamino by a piperidino group in the phenglutarimide molecule did not affect markedly the potencies of the high affinity enantiomer. In contrast, replacement of the phenyl by a cyclohexyl ring decreased 20 fold the active enantiomers potency. Methylation of the piperidine-2,6-dione nitrogen also reduced markedly the eutomers' affinities, more on the M1 than on the other subtypes. 5. The selectivity profiles (recognition of four receptor subtypes) of six of the seven less active enantiomers were different from the corresponding more active enantiomers selectivity profiles, suggesting that the preparations used in this study were pure. However, we cannot not exclude the hypothesis that the batch of (S)-thienglutarimide used in this study was contaminated by less than 0.02% of the eutomer. 6. In contrast with the eutomer binding site, replacement of the phenyl ring by a thienyl or cyclohexyl ring did not affect binding of the low affinity enantiomers to the muscarinic receptor or the [3H]-NMS-receptor complex. The replacement of the diethylamino group by a piperidine ring, and N-methylation of the piperidine-2,6 dione moiety increased slightly these enantiomers' potencies. 7. The muscarinic receptors were extremely stereoselective, and had up to 20000 fold lower affinity for the less active enantiomers. However, the stereochemical requirements of the muscarinic receptor subtypes were different for the enantiomers of compounds 1-7, being most stringent at M1 receptors. 8. The weaker enantiomers behaved as competitive antagonists in pharmacological studies, at least in the concentration-range investigated.

Vasoconstrictor and vasodilator responses to various agonists in the rat perfused mesenteric arterial bed: selective inhibition by PPADS of contractions mediated via P2x-purinoceptors.

1. The effect of pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on vasoconstrictor and/or vasodilator responses to various agonists and electrical field stimulation was investigated in the rat mesenteric arterial bed at basal tone and at tone raised by methoxamine (15-50 microM). 2. At basal tone, nucleotides produced vasoconstriction with the following rank order of potency: alpha,beta-methylene ATP >> 2-methylthio ATP > or = ATP = UTP. PPADS (0.3-10 microM) concentration-dependently antagonized alpha, beta-methylene ATP-, 2-methylthio ATP- and ATP-induced responses. UTP-, noradrenaline- and nerve-mediated (4-32 Hz) increases in perfusion pressure remained unaffected by 10 microM PPADS. 3. In raised tone preparations, nucleotides produced vasodilations, their rank order of potency being 2-methylthio ATP > ATP > UTP. Responses to 2-methylthio ATP were slightly antagonized, whereas ATP- and UTP-induced responses remained unaffected by 10 microM PPADS. In addition, acetylcholine- and adenosine-elicited relaxations were not influenced by 10 microM PPADS. 4. The present results confirm the previously described selective P2x antagonism by PPADS, this compound being ineffective at muscarinic M3- and adenosine P1-receptors as well as at alpha 1-adrenoceptors. There was some inhibition of P2y-purinoceptors but at a much higher concentration than required for inhibition of P2x-purinoceptors. 5. In addition, this study provides evidence for the ineffectiveness of PPADS at both vasoconstriction- and vasodilatation-mediating P2u-purinoceptors.

Vasoconstrictor responses via P2X-receptors are selectively antagonized by NF023 in rabbit isolated aorta and saphenous artery.

1. The effects of NF023, the symmetrical 3'-urea of 8-(benzamido)naphthalene-1,3,5-trisulphonic acid), and its parent compound suramin were investigated on vasoconstrictor responses to alpha, beta-methylene ATP in rabbit isolated saphenous artery and vasodilator responses to ATP in noradrenaline-precontracted rabbit isolated thoracic aorta. 2. In rabbit isolated saphenous artery, alpha, beta-methylene ATP-induced vasoconstrictor responses via P2X-receptors were concentration-dependently and competitively antagonised by NF023 (30-300 microM; pA2 = 5.69 +/- 0.04). Suramin (100-1000 microM) also competitively blocked vasoconstrictor responses to alpha, beta-methylene ATP, albeit with lower potency (pA2 = 4.79 +/- 0.05). In contrast, NF023 (100 microM) did not significantly affect contractile responses to noradrenaline or histamine in the saphenous artery. 3. In noradrenaline-precontracted rabbit isolated thoracic aorta preparations, ATP (3-3000 microM) concentration-dependently induced relaxations via endothelium-dependent or smooth muscle P2Y-receptor subtypes. NF023 (30-300 microM) failed to block relaxant responses to ATP at endothelium-dependent P2Y-receptors, whereas suramin (100-1000 microM) did antagonise endothelium-dependent vasodilator responses to ATP. Neither NF023 (100 microM) nor suramin (300 microM) influenced vasorelaxant responses to ATP via endothelium-independent P2Y-receptors. 4. In conclusion, this study outlines the selectivity of NF023 as an effective P2X-receptor antagonist in rabbit isolated blood vessels without affecting endothelium-dependent or endothelium-independent P2Y-receptor subtypes, adrenoceptors or histamine receptors.

Binding and functional properties of hexocyclium and sila-hexocyclium derivatives to muscarinic receptor subtypes.

1. We have compared the binding properties of several hexocyclium and sila-hexocyclium derivatives to muscarinic M1 receptors (in rat brain, human neuroblastoma (NB-OK 1) cells and calf superior cervical ganglia), rat heart M2 receptors, rat pancreas M3 receptors and M4 receptors in rat striatum, with their functional antimuscarinic properties in rabbit vas deferens (M1/M4-like), guinea-pig atria (M2), and guinea-pig ileum (M3) muscarinic receptors. 2. Sila-substitution (C/Si exchange) of hexocyclium (-->sila-hexocyclium) and demethyl-hexocyclium (-->demethyl-sila-hexocyclium) did not significantly affect their affinities for muscarinic receptors. By contrast, sila-substitution of o-methoxy-hexocyclium increased its affinity 2 to 3 fold for all the muscarinic receptor subtypes studied. 3. The p-fluoro- and p-chloro-derivatives of sila-hexocyclium had lower affinities than the parent compound at the four receptor subtypes, in binding and pharmacological studies. 4. In binding studies, o-methoxy-sila-hexocyclium (M1 = M4 > or = M3 > or = M2) had a much lower affinity than sila-hexocyclium for the four receptor subtypes, and discriminated the receptor subtypes more poorly than sila-hexocyclium (M1 = M3 > M4 > M2). This is in marked contrast with the very clear selectivity of o-methoxy-sila-hexocyclium for the prejunctional M1/M4-like heteroreceptors in rabbit vas deferens. 5. The tertiary amines demethyl-hexocyclium, demethyl-sila-hexocyclium and demethyl-o-methoxy-sila-hexocyclium had 10 to 30 fold lower affinities than the corresponding quaternary ammonium derivatives.