Acetylcholine receptors (muscarinic) (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database

Muscarinic acetylcholine receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Muscarinic Acetylcholine Receptors [45]) are GPCRs of the Class A, rhodopsin-like family where the endogenous agonist is acetylcholine. In addition to the agents listed in the table, AC-42, its structural analogues AC-260584 and 77-LH-28-1, N-desmethylclozapine, TBPB and LuAE51090 have been described as functionally selective agonists of the M1 receptor subtype via binding in a mode distinct from that utilized by non-selective agonists [243, 242, 253, 155, 154, 181, 137, 11, 230]. There are two pharmacologically characterised allosteric sites on muscarinic receptors, one defined by it binding gallamine, strychnine and brucine, and the other defined by the binding of KT 5720, WIN 62,577, WIN 51,708 and staurosporine [161, 162].

Synthesis and SAR of 2-aryl pyrido[2,3-d]pyrimidines as potent mGlu5 receptor antagonists

A novel series of potent 2-aryl pyrido[2,3-d]pyrimidine mGlu5 receptor antagonists are described. The synthesis and pharmacological activities of these analogs are discussed.

Rational design of 7-arylquinolines as non-competitive metabotropic glutamate receptor subtype 5 antagonists

Rational replacement of the alkyne linker of mGluR5 antagonist MPEP gave 7-arylquinolines. SAR optimization gave an orally active compound with high affinity for the MPEP binding site.

Comparison of different substances for subureteric injection in the management of vesicoureteric reflux in children

INTRODUCTION

Endoscopic techniques are becoming increasingly accepted for treatment of vesicoureteric reflux as alternatives to open surgical reimplantation. However, there is some debate about the ideal injectable material. Since we have accumulated experience with several substances, an opportunity existed to compare them.

MATERIALS AND METHODS

From 1991 to 2003, 101 children with vesicoureteric reflux were treated by endoscopic subureteric injection either once (74) or twice (27) by either of two pediatric urologists. There were a total of 165 ureteral injections, 83 with polytetrafluoroethylene (Teflon), 73 with polydimethylsiloxane (Macroplastique), and 9 with collagen. Each child was evaluated pre-operatively and 3 months post-operatively with a nuclear cystogram and renal ultrasonography.

RESULTS

The polytetrafluoroethylene and polydimethylsiloxane groups were not significantly different with respect to sex, age, indication for surgery, severity of reflux or prior surgeries. The collagen group overall did very poorly with only 3 of 9 refluxing ureters cured. The other two substances had much more success with 61% of ureters in the polytetrafluoroethylene group cured on first injection and 75% with polydimethylsiloxane, plus another 19% and 11% cured on second attempt, respectively (total 80% and 86%).

CONCLUSIONS

Subureteric injections of polytetrafluoroethylene and polydimethylsiloxane are very effective at curing vesicoureteric reflux in children with little morbidity. When comparing individual cases, ureters, and all grades of reflux, polytetrafluoroethylene and polydimethylsiloxane have similar success rates. Collagen injections were less successful, and patients with neurogenic bladders had poor results.

Synthesis and pharmacology of benzoxazines as highly selective antagonists at M(4) muscarinic receptors

Previously, we reported on PD 102807 (41) as being the most selective synthetic M(4) muscarinic antagonist identified to date. Synthesized analogues of 41 showed no improvement in affinity and selectivity at that time. However, several newly synthesized compounds exhibit a 7-fold higher affinity at M(4) receptors and demonstrate a selectivity of at least 100-fold over all other muscarinic receptor subtypes. For example, compound 28 showed an affinity of pK(i) = 9.00 at M(4) receptors and a selectivity of M(1)/M(4) = 13 183-fold, M(2)/M(4) = 339-fold, M(3)/M(4) = 151-fold, and M(5)/M(4) = 11 220-fold. This high selectivity along with high affinity has not been reported for any synthetic muscarinic antagonist, nor for natural occurring M(4) antagonists such as the M(4) selective Eastern Green Mamba venom MT3 (M(4) pK(b) = 8.7, M(1)/M(4) = 40-fold, M(2)/M(4) > or = 500-fold, M(3)/M(4) > or = 500-fold, and M(5)/M(4) > or = 500-fold). Derivative 24, a compound with a high selectivity pattern as well, has been tested for in vivo efficacy. It was able to block the L-3,4-dihydroxyphenylalanine accumulation produced by CI-1017, an M(1)/M(4) selective muscarinic agonist, in the mesolimbic region and striatum, which suggests that 24 is capable of crossing the blood-brain barrier and confirms the pharmacokinetic data obtained on this compound. This is evidence that suggests that agonist-induced increase in catecholamine synthesis observed in these regions is mediated by M(4) receptors.

Evidence for seeding of beta -amyloid by intracerebral infusion of Alzheimer brain extracts in beta -amyloid precursor protein-transgenic mice

Many neurodegenerative diseases are associated with the abnormal sequestration of disease-specific proteins in the brain, but the events that initiate this process remain unclear. To determine whether the deposition of the beta-amyloid peptide (Abeta), a key pathological feature of Alzheimer's disease (AD), can be induced in vivo, we infused dilute supernatants of autopsy-derived neocortical homogenates from Alzheimer's patients unilaterally into the hippocampus and neocortex of 3-month-old beta-amyloid precursor protein (betaAPP)-transgenic mice. Up to 4 weeks after the infusion there was no Abeta-deposition in the brain; however, after 5 months, the AD-tissue-injected hemisphere of the transgenic mice had developed profuse Abeta-immunoreactive senile plaques and vascular deposits, some of which were birefringent with Congo Red. There was limited deposition of diffuse Abeta also in the brains of betaAPP-transgenic mice infused with tissue from an age-matched, non-AD brain with mild beta-amyloidosis, but none in mice receiving extract from a young control case. Abeta deposits also were not found in either vehicle-injected or uninjected transgenic mice or in any nontransgenic mice. The results show that cerebral beta-amyloid can be seeded in vivo by a single inoculation of dilute AD brain extract, demonstrating a key pathogenic commonality between beta-amyloidosis and other neurodegenerative diseases involving abnormal protein polymerization. The paradigm can be used to clarify the conditions that initiate in vivo beta-amyloidogenesis in the brain and may yield a more authentic animal model of Alzheimer's disease and other neurodegenerative disorders.

CI-1017, a functionally M1-selective muscarinic agonist: design, synthesis, and preclinical pharmacology

The five muscarinic receptor subtypes (M1-M5) are characterized by seven helices that define a transmembrane cavity which serves as the binding pocket for agonists and antagonists. The five cavities appear to be topographically different enough to permit subtype selectivity among antagonists but not among classical agonists which tend to be smaller in size than antagonists. It was reasoned that synthesis of muscarinic agonists longer/larger than their classical counterparts might result in subtype selectivity. M1 subtype selectivity was found in a class of 1-azabicyclo[2.2.1]heptan-3-one, O-(3-aryl-2-propynyl) oximes. One of these, CI-1017, improved spatial memory of hippocampally deficient mice and nbM-lesioned rats at doses of 1.0-3.2 and 0.1-0.3 mg/kg, respectively, while producing parasympathetic side effects only at very high doses (100-178 mg/kg). Additionally, CI-1017 inhibited production of amyloidogenic A beta and increased secretion of soluble APP. Thus, CI-1017, besides treating AD symptomatically, may also retard its progression. CI-1017 has recently completed phase I clinical trials.

The M1 muscarinic agonist CI-1017 facilitates trace eyeblink conditioning in aging rabbits and increases the excitability of CA1 pyramidal neurons

The M1 muscarinic agonist CI-1017 was administered intravenously to aging rabbits on a daily basis before and during hippocampally dependent trace eyeblink conditioning sessions. Circulating levels of CI-1017 were significantly related to the drug dose. The drug was found to significantly increase the rate and amount of learning in a dose-dependent manner with no significant effects on the amplitude, area, or latency of conditioned responses. There was no evidence of pseudoconditioning at the highest drug concentration, and the minimally effective dose produced only mild and temporary hypersalivation as a side effect. CI-1017 (10 microM) was also found to increase the excitability of CA1 pyramidal neurons recorded from hippocampal slices from young and aging naive rabbits as measured by changes in spike-frequency adaptation and the postburst afterhyperpolarization. These biophysical changes were reversed with either atropine (1 microM) or pirenzepine (1 microM). These results suggest that M1 agonists ameliorate age-related learning and memory impairments at least in part by reducing the afterhyperpolarization and spike-frequency adaptation of hippocampal pyramidal neurons and that M1 agonists may be an effective therapy for reducing the cognitive deficits that accompany normal aging and/or Alzheimer's disease.

Milameline (CI-979/RU35926): a muscarinic receptor agonist with cognition-activating properties: biochemical and in vivo characterization

Milameline (E-1,2,5,6-tetrahydro-1-methyl-3-pyridinecarboxaldehyde, O-methyloxime monohydrochloride, CI-979, PD129409, RU35926) was characterized in vitro and evaluated for effects on central and peripheral cholinergic activity in rats and rhesus monkeys. In muscarinic binding studies, milameline displayed nanomolar affinity with an agonist ligand and micromolar affinity with antagonist ligands, with approximately equal affinities determined at the five subtypes of human muscarinic receptors (hM(1)-hM(5)) with whole cells or membranes from stably transfected Chinese hamster ovary (CHO) cells. On binding, milameline stimulated phosphatidylinositol hydrolysis in hM(1) and hM(3) CHO cells and inhibited forskolin-activated cAMP accumulation in hM(2) and hM(4) CHO cells. Additionally, it decreased K(+)-stimulated release of [(3)H]acetylcholine from rat cortical slices. Responses were not caused by the inhibition of acetylcholinesterase, and there was no significant binding to approximately 30 other neurotransmitter binding sites. In rats, milameline decreased spontaneous and scopolamine-induced swimming activity, improved water-maze performance of animals impaired by basal forebrain lesions, increased cortical blood flow, decreased core body temperature, and increased gastrointestinal motility. Electroencephalogram activity in both rats and monkeys was characterized by a predominance of low-voltage desynchronized activity consistent with an increase in arousal. Milameline also reversed a scopolamine-induced impairment of attention on a continuous-performance task in monkeys. Thus, milameline possesses a pharmacological profile consistent with that of a partial muscarinic agonist, with central cholinergic actions being produced in rats and monkeys at doses slightly lower than those stimulating peripheral cholinergic receptors.

Design and synthesis of novel quinoxaline-2,3-dione AMPA/GlyN receptor antagonists: amino acid derivatives

PNQX (1,4,7,8,9,10-hexahydro-9-methyl-6-nitropyrido[3, 4-f]quinoxaline-2,3-dione) is a potent AMPA (IC50 = 0.063 microM) and GlyN (IC50 = 0.37 microM) receptor antagonist that was developed in our laboratories. While possessing a desirable in vitro and in vivo activity profile, this compound suffers from low aqueous solubility. In an effort to improve its potency and physical properties, we have designed and synthesized novel ring-opened analogues 4, 6, 9, and 11. Modeling analyses demonstrated that, while the 5-substituent in these analogues was forced to adopt an out-of-plane conformation due to steric contacts with neighboring substituents, the overall structure retained a good fit to a previously described AMPA pharmacophore model. This nonplanar orientation may lessen efficient packing in the solid state, compared to PNQX, leading to increased water solubility. Indeed, several nonplanar analogues containing appropriate functionalities, for example, the sarcosine analogue 9, were found to retain AMPA (IC50 = 0.14 microM) and GlyN (IC50 = 0.47 microM) receptor affinity and possess improved aqueous solubility compared to PNQX. The synthesis and the SAR of these compounds are discussed.

Inhibitors of V-type ATPases, bafilomycin A1 and concanamycin A, protect against beta-amyloid-mediated effects on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction

The functional viability of cells can be evaluated using a number of different assay determinants. One common assay involves exposing cells to 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), which is converted intracellularly to a colored formazan precipitate and often used to assess amyloid peptide-induced cytotoxic effects. The MTT assay was employed to evaluate the role of endosomal uptake and lysosomal acidification in amyloid peptide-treated differentiated PC12 cell cultures using selective vacuolar-type (V-type) ATPase inhibitors. The macrolides bafilomycin A1 (BAF) and concanamycin A (CON) block lysosomal acidification through selective inhibition of the V-type ATPase. Treating nerve growth factor-differentiated PC12 cells with nanomolar concentrations of BAF or CON provides complete protection against the effects of beta-amyloid peptides Abeta(1-42), Abeta(1-40), and Abeta(25-35) and of amylin on MTT dye conversion. These macrolides do not inhibit peptide aggregation, act as antioxidants, or inhibit Abeta uptake by cells. Measurements of lysosomal acidification reveal that the concentrations of BAF and CON effective in reversing Abeta-mediated MTT dye conversion also reverse lysosomal pH. These results suggest that lysosomal acidification is necessary for Abeta effects on MTT dye conversion.

Mutations of aspartate 103 in the Hm2 receptor and alterations in receptor binding properties of muscarinic agonists

Aspartate 103 (D103) in the third transmembrane domain of the Hm2 receptor was mutated to glutamate (D103E), asparagine (D103N), or alanine (D103A). As measured by [3H]-NMS, no significant binding was observed in D103A, while a 2-fold decrease in ligand affinity was seen in D103E and a 32-fold decrease in affinity was found in the D103N mutant. Examination of reference agonists showed greater loss of affinity in D103N than in D103E with the rank order of change being: L-607,207>carbachol>arecoline>pilocarpine>oxotremorine>McN-A-343. Of the novel 1-azabicyclo[2.2.1]-heptan-3-one oxime agonists examined, arylacetylene oximes showed little alteration in binding in either the D103E or D103N mutants, while the geometric isomers of several bicyclic aryl-ene-yne oximes showed significant changes in affinity, especially in the D103N mutant. Thus, overall size of the agonist and/or spatial orientation of the molecule within the binding pocket contribute to changes measured in binding.

Preclinical and phase 1 clinical characterization of CI-979/RU35926, a novel muscarinic agonist for the treatment of Alzheimer's disease

In vitro and in vivo characterization in rodents and monkeys shows that CI-979/RU35926 is a partial muscarinic agonist with equal affinity for the five subtypes of muscarinic receptors. It activates central cholinergic receptors as shown by its ability to decrease body temperature, enhance local cortical blood flow and increase cortical arousal measured by QEEG. Further, it reverses spatial memory deficits in rats with ibotenic acid-induced lesions of forebrain cholinergic neurons. Signs of peripheral cholinergic stimulation appear at doses higher or equal to those necessary to produce central activity. In a single-dose tolerance study in young, healthy human volunteers, CI-979/RU35926 was well tolerated at doses of 0.002-1.0 mg with cholinergic symptoms such as hypersalivation and sweating, observed at 2-4 mg. It demonstrated linear pharmacokinetic behavior over a dose range of 0.1 to 4 mg and elimination half-life varied from 2-5 hours. Measurement of unchanged drug in urine suggests that the drug was extensively metabolized. Thus, the safety profile supported further clinical evaluation and CI-979/RU35926 is currently in Phase II clinical trials.

Identification and characterization of m1 selective muscarinic receptor antagonists1

A series of esters of 1,4-disubstituted tetrahydropyridine carboxylic acids (I) has been synthesized and characterized as potential m1 selective muscarinic receptor antagonists. The affinity of these compounds for the five human muscarinic receptor subtypes (Hm1-Hm5) was determined by the displacement of [3H]-NMS binding using membranes from transfected Chinese hamster ovarian cells. One of the most potent and selective compounds of this series is an analogue of I [11, R1 = (CH2)5CH3], which has an IC50 value of 27.3 nM at the m1 receptor and possesses 100-fold (m2), 48-fold (m3), 74-fold (m4), and 19-fold (m5) selectivities at the other receptors. Thus, this analogue appears to be more selective on the basis of binding than the prototypical m1 antagonist, pirenzepine. Functional data, such as the inhibition of carbachol-stimulated phosphatidylinositol hydrolysis, on selected analogues confirmed the muscarinic antagonistic properties of this chemical series.

Differential expression of group I metabotropic glutamate receptors (mGluRs) in the rat pheochromocytoma cell line PC12: role of nerve growth factor and ras

Glutamate treatment of PC12 cells has been shown to result in the accumulation of intracellular inositol phosphates suggesting the presence of glutamate metabotropic receptors (mGluRs) positively coupled to phospholipase C. The present study examined the expression of group I mGluRs (mGluR1 and mGluR5) in PC12 cells. Undifferentiated PC12 cells were found to express both mGluR5 mRNA and receptor protein by reverse transcription polymerase chain reaction (RT-PCR) and western blot techniques. However, mGluR1 mRNA was not detected in these cells and western blot analysis showed only faint mGluR1alpha immunoreactivity suggesting a very low level of mGluR1 expression. Nerve growth factor-induced differentiation of PC12 cells resulted in the induction of mGluR1alpha and mGluR1beta mRNA and mGluR1alpha protein. PC12 cells overexpressing dominant negative ras revealed that NGF-induced mGluR1 induction, but not mGluR5 expression, is dependent on ras pathway activation in these cells. These results suggest PC12 cells may be a useful model for investigating the regulation and expression of group I mGluR isoforms and their role in neuronal processes in vitro.

Identification and characterization of m4 selective muscarinic antagonists

Our interest in the area of m4 muscarinic antagonists had led us to study a series of benzoxazine isoquinolines. One of the most potent and selective compounds of this series is example 1 with an IC50 value of 90.7 nM at m4 receptors, and 72-fold (m1), 38-fold (m2), 10-fold (m3), and 82-fold (m5) more selective compared to the other receptors. The synthesis and receptor binding affinity of analogs of 1 are reported.

Design and synthesis of m1-selective muscarinic agonists: (R)-(-)-(Z)-1-Azabicyclo[2.2.1]heptan-3-one, O-(3-(3'-methoxyphenyl)-2-propynyl)oxime maleate (CI-1017), a functionally m1-selective muscarinic agonist

The synthesis and SAR of a series of (Z)-(+/-)-1-azabicyclo[2.2. 1]heptan-3-one, O-(3-aryl-2-propynyl)oximes are described. The biochemistry and pharmacology of 24Z (PD 142505) and its enantiomers are highlighted. 24Z is functionally an m1-selective muscarinic agonist. Efficacy and m1 selectivity reside in the R enantiomer, (R)-24Z (CI-1017).

Acute epididymitis in boys: are antibiotics indicated?

OBJECTIVES

To report the results of using supportive therapy only, rather than antibiotics, in managing boys with acute sterile epididymitis.

PATIENTS AND METHODS

From 1991 to 1995, 48 boys presented with acute epididymitis. The diagnosis was confirmed by radionuclide scan in 43 cases, ultrasonography in one, surgical exploration in one and physical examination in three. Urine was collected for microscopy and culture: if pyuria was detected, antibiotics were prescribed. If the urine analysis was normal, the patient was advised to minimize physical activity and analgesics were prescribed.

RESULTS

Of the 48 boys, five (10%) had pyuria; seven patients with either no urine tested or negative urine culture were given antibiotics. The remaining 36 were managed with supportive therapy only. The mean follow-up was 87 days (with three patients lost to follow-up). No boys showed any evidence of testicular atrophy or other complications.

CONCLUSION

Only a minority of boys with acute epididymitis, as defined by increased flow on radionuclide scanning of the scrotum, have a bacterial aetiology. For those without pyuria or positive urine culture, the condition is self-limiting and does not lead to testicular atrophy. We recommend that for boys with acute epididymitis who have no urinary abnormalities, antibiotics are not indicated. The aetiology of acute sterile epididymitis in boys remains obscure.

A structure-activity relationship study of novel phenylacetamides which are sodium channel blockers

A structure-activity relationship study of a series of novel Na(+) channel blockers, structurally related to N-[3-(2,6-dimethyl-1-piperidinyl)propyl]-alpha-phenylbenzeneacetamide (1, PD85639) is described. The diphenylacetic acid portion of the molecule was left unchanged throughout the study, while structural features in the amine portion and the amide alkyl linkage of the molecule were modified. The compounds were tested for inhibition of veratridine-stimulated Na(+) influx in CHO cells expressing type IIA Na(+) channels. Several derivatives show a trend toward more potent Na+ channel blockade activity with increasing lipophilicity of the amine portion of the molecule. The presence of a phenyl ring near the amine increases inhibitory potency. A three-carbon spacer between the amide and amine is optimal, and a secondary amide linkage is preferred.

Substituted 2-benzothiazolamines as sodium flux inhibitors: quantitative structure-activity relationships and anticonvulsant activity

Thirty-two aryl-substituted 2-benzothiazolamines have been tested for their ability to modulate sodium flux in rat cortical slices. A QSAR analysis, applied to these derivatives, showed a trend toward increasing potency as sodium flux inhibitors with increasing lipophilicity, decreasing size, and increasing electron withdrawal of the benzo ring substituents. Additionally, 4- or 5-substitution of the benzo ring was found to decrease potency. The combination of increased lipophilicity, small size, and electron withdrawal severely limited which groups were tolerated on the benzo ring, thus suggesting that the optimal substitution patterns have been prepared within this series. Nine of these compounds were potent inhibitors of veratridine-induced sodium flux (NaFl). These nine compounds also proved to be anticonvulsant in the maximal electroshock (MES) assay. Fourteen additional 2-benzothiazolamines demonstrated activity in the MES screen, yet exhibited no activity in the NaFl assay. These derivatives may be interacting at the sodium channel in a manner not discernible by the flux paradigm, or they may be acting by an alternative mechanism in vivo.

PD 142676 (CI 1002), a novel anticholinesterase and muscarinic antagonist

Inhibition of brain acetylcholinesterase (AChE) can provide relief from the cognitive loss associated with Alzheimer's disease (AD). However, unwanted peripheral side effects often limit the usefulness of the available anticholinesterases. Recently, we identified a dihydroquinazoline compound, PD 142676 (CI 1002) that is a potent anticholinesterase and a functional muscarinic antagonist at higher concentrations. Peripherally, PD 142676, unlike other anticholinesterases, inhibits gastrointestinal motility in rats, an effect consistent with its muscarinic antagonist properties. Centrally, the compound acts as a cholinomimetic. In rats, PD 142676 decreases core body temperature. It also increases neocortical arousal, as measured by quantitative electroencephalography, and cortical acetylcholine levels, measured by in vivo microdialysis. The compound improves the performance of C57/B10j mice in a water maze task and of aged rhesus monkeys in a delayed match-to-sample task involving short-term memory. The combined effect of AChE inhibition and muscarinic antagonism distinguishes PD 142676 from other anticholinesterases, and may be useful in treating the cognitive dysfunction of AD and produce fewer peripheral side effects.

Synthesis and pharmacological evaluation of phenylacetamides as sodium-channel blockers

The synthesis and structure-activity relationships of a series of phenylacetamides related to N-[3-(2,6-dimethyl-1-piperidinyl)propyl]-alpha-phenylbenzeneacetamide (1) (PD85639) acting at the voltage-dependent Na+ channel are described. All structural variations for this study were made in the phenylacetic acid portion of these molecules, and the compounds were synthesized by coupling the appropriately substituted phenylacetic acid derivative with 3-[1-(2,6-dimethyl)piperidinyl]-propanamine using standard methods of amide formation. Compounds were tested as inhibitors of [3H]batrachtoxinin binding in rat neocortical membranes and also as inhibitors of veratridine-induced Na+ influx in Chinese hamster ovary cells expressing type IIA Na+ channels. Diphenylacetic acid derivatives with halogenated aromatic rings (12-15) were very potent in both assays, while alkoxy and alkyl substitution did not affect activity (16 and 17). Selected compounds were tested as potential neuroprotective agents in two cell culture assays involving inhibition of veratridine-induced and hypoxia-induced lactate dehydrogenase release. Compound 15 was equipotent with flunarizine, a reference compound in both neuroprotection assays.

Specific binding of the novel Na+ channel blocker PD85,639 to the alpha subunit of rat brain Na+ channels

The local anesthetic-like Na+ channel-blocking drug [3H]PD85639 [alpha-([4-3H]phenyl)-N-[3-(2,6-dimethyl-1-piperizinyl)-alpha-prop yl] [4-3H]benzeneacetamide] binds specifically to receptor sites on Na+ channels in intact synaptosomes and synaptosomal membranes, purified and reconstituted Na+ channels, and type IIA Na+ channel alpha subunits expressed in the transfected Chinese hamster ovary cell line CNaIIA-1. No specific binding was observed in nontransfected CHO-K1 cells, confirming the specificity of binding to Na+ channels. Two classes of binding sites that differed in affinity and dissociation rate were observed in all three preparations. In synaptosomes, the high affinity sites had Kd values of 3-20 nM and a Bmax of approximately 0.2 pmol/mg, whereas the low affinity sites had Kd values of 0.4-20 microM and a Bmax of approximately 5 pmol/mg. Binding of PD85,639 was inhibited by the local anesthetics tetracaine, bupivacaine, and mepivacaine at concentrations in the same range as those that inhibit Na+ channels. Tetracaine did not affect the dissociation rate of PD85,639, consistent with competitive binding of these two drugs at the same receptor site. In contrast, binding of PD85,639 was unaffected by the anticonvulsants phenytoin and carbamazepine, which also inhibit Na+ channels. Veratridine and batrachotoxin, which bind at neurotoxin receptor site 2 on Na+ channels, inhibited specific PD85,639 binding completely. PD85,639 accelerated dissociation of specifically bound batrachotoxin, consistent with an indirect allosteric interaction between these two compounds. Thus, like local anesthetics, PD85,639 inhibits binding of batrachotoxin by an allosteric mechanism. The results indicate that PD85,639 binds specifically to a local anesthetic receptor site on the Na+ channel alpha subunit that is allosterically linked to neurotoxin receptor site 2. PD85,639 may be a useful molecular probe of this important drug receptor site on the Na+ channel.

Characterization of muscarinic agonists in recombinant cell lines

Using recombinant CHO cells that express Hm1-Hm5 receptors, reference muscarinic agonists have been characterized with respect to their activity in receptor binding and second messenger assays. In whole cell [3H]-N-methyl scopolamine binding, no agonist was found to be truly subtype selective, although some showed marked differences between several of the subtypes (e.g. m1 vs. m2). As a functional index of receptor activation, phosphatidyl-inositol (PI) turnover was measured for m1, m3, and m5 receptors while inhibition of forskolin-stimulated cAMP accumulation was measured for m2 and m4 receptors. Both full and partial agonists were delineated in PI turnover, but all agonists showed similar responses on cAMP. Alkylation studies with propylbenzylcholine mustard showed that both efficacy and potency were markedly affected in the functional assays by the number of free receptors. Thus, receptor reserve appears to play a major role in the determination of subtype selectivity for agonists using functional measures. Even with these limitations, however, the use of transformed cell lines is playing a pivotal role in the discovery of selective agonists.

Synthesis and SAR of bulky 1-azabicyclo[2.2.1]-3-one oximes as muscarinic receptor subtype selective agonists

The synthesis of a series of potent and efficacious 1-azabicyclo[2.2.1]heptan-3-one oxime muscarinic agonists is described. The oximes have extended appendages designed to span the cavity defined by the seven transmembrane helices of the muscarinic receptor. Some members of the series are selective for receptors of the m1 subtype. One such oxime, 31, shows affinity and functional selectivity for m1 over m2, m3, and m4 muscarinic receptor types.

Structure-activity studies on benzhydrol-containing nipecotic acid and guvacine derivatives as potent, orally-active inhibitors of GABA uptake

The introduction of lipophilic groups onto the ring nitrogen of nipecotic acid and guvacine, two known GABA uptake inhibitors, afforded potent, orally-active anticonvulsant drugs. A series of compounds is reported which explores the structure-activity relationships (SAR) in this series. Among the areas explored: side-chain SAR (aromatic-, heterocyclic-, and tricyclic-containing side chains) and modifications to the tetrahydropyridine ring. The benzhydrol ether-containing side chains afforded the most potent compounds with several exhibiting in vitro IC50 values for GABA uptake of < 1 microM (including 5, Table I; 37, 43, Table IV; and 44, Table V). Compound 44 was selected for extensive evaluation and subsequently progressed to Phase 1 clinical trials with severe adverse effects seen after single dose administration to humans.

Cholinergic agents: effect of methyl substitution in a series of arecoline derivatives on binding to muscarinic acetylcholine receptors

Arecoline, arecaidine, and a series of derivatives, differing by the presence or absence of methyl groups at positions on the periphery of the molecule, were prepared, and their binding to muscarinic acetylcholine receptors was tested. On the basis of this study, muscarinic agonism for arecoline series is governed by strict structure-activity relationships, as previously observed for other agonist series. Only minor changes in nitrogen substitution were tolerated in the present series of arecoline derivatives.

A silica gel plate-based qualitative assay for acetylcholinesterase activity: a mass method to screen for potential inhibitors

A procedure for the qualitative assessment of inhibitory activity towards acetylcholinesterase for a given compound is described. Solutions of the compounds of interest are spotted on silica gel TLC plates in a matrix pattern. The silica gel plate is sprayed with a solution of acetylthiocholine iodide and 5,5-dithiobis(2-nitrobenzoic acid) followed by a solution of acetylcholinesterase. The enzyme reaction produces a yellow background color with inhibitor compounds exposed as white zones where color has failed to develop. The results for a test set of compounds were compared to those obtained using the standard Ellman assay procedure and found to agree for virtually all of these compounds. The conditions of silica gel plate thickness, reagent concentration, and enzyme source under which this procedure is suitable were investigated. This represents an extremely rapid method to screen large numbers of compounds to uncover new inhibitors of acetylcholinesterase and potentially other enzymes as well.

Loss of muscarinic M1 receptors with aging in the cerebral cortex of Fisher 344 rats

Age-related changes in central cholinergic muscarinic receptors were measured in young (3-6 month), middle-aged (15-17 month), and aged (22-26 month) male Fisher 344 rats by receptor binding techniques. Using [3H]-quinuclidinyl benzilate as the ligand, a significant decrease (14-19%) in the number of muscarinic cortical receptors was measured in aged rats compared to both young and middle-aged rats. With the selective M1 antagonist, [3H]-pirenzepine, a 17% decrease in receptor density was observed in the cortex of aged animals compared to young rats. For both ligands no differences were observed in the striatum or hippocampus between any age group and there was no change in affinity (Kd) in any of the three brain regions for the three age groups. Additionally, there was no difference in choline acetyltransferase activity measured in cortex, hippocampus, or striatum of young and aged rats. Thus, there is a loss of M1 muscarinic receptors in the cerebral cortex of aged male Fisher 344 rats.

Acute scrotal pain in children: prospective study of diagnosis and management

Forty-eight boys were assessed for an acutely painful scrotum. Thirty-six (75%) of them underwent radionuclide scanning of the scrotum; the average age of this group was 11 years. The scan revealed epididymitis in 19 cases, spermatic cord torsion in 9, appendix testis torsion in 7 and acute hernia-hydrocele in 1. The diagnosis was confirmed at operation in all nine cases of spermatic cord torsion. Boys who had epididymitis received antibiotics only; all were available for short-term follow-up, and 16 were also assessed at a mean of 6 months after infection. Only one boy had testicular atrophy; he had undergone repair of an inguinal hernia, which could not be ruled out as a cause. Bacteriuric epididymitis occurred in three boys; two had known predisposing genitourinary anomalies, the third had no abnormalities. Boys who had nonbacteriuric epididymitis were investigated by renal and pelvic ultrasonography or voiding cystourethrography; no important abnormalities were detected. This prospective study indicates that radionuclide scanning can reliably differentiate spermatic cord torsion from other acute scrotal disease.

An in-vivo method for testing drugs that influence striatal dopaminergic functions

A procedure is described for evaluating the effects of drugs on dopaminergic function in the striatum of mice. Mice, anesthetized with chloral hydrate are injected with 6-hydroxydopamine into one striatum to destroy dopamine nerve terminals at this site. Several days later, the mice are anesthetized with halothane, and test drugs or saline are injected into the intact striatum either before or after the systemic administration of amphetamine. The effect of these drugs on amphetamine-induced circling behavior is evaluated. Using this model, we have found that pilocarpine and muscimol can inhibit amphetamine-induced circling and their effects are blocked by the systemic administration of scopolamine and picrotoxin, respectively. In addition, ethyleneglycol-bis-(beta-amino-ethyl ether) N,N'-tetraacetic acid (EGTA), a calcium chelating agent, inhibited amphetamine-induced circling behavior and this effect is prevented by adding calcium to the EGTA solution. Finally, the intrastriatal administration of prostaglandin E2 but not its metabolite, 13,14-dihydro-15-keto-prostaglandin E2 inhibited amphetamine-induced circling suggesting a selective effect of the active prostaglandin. These results suggest that this procedure could be used for evaluating both the mechanism of action of drugs in the striatum as well as screening drugs for their therapeutic potential.

Prostaglandin inhibition of apomorphine-induced circling in mice

The effect of prostaglandins (PGs) on apomorphine (apo)-induced circling was examined in unilaterally lesioned mice. Intraventricularly injected PGD2, PGE2, and PGF2 alpha at a dose of 1.0 nmole/g all inhibited apo-induced circling. When injected directly into the striatum, these same PGs also inhibited circling in a dose range of 0.01-0.1 nmole/g, while the PGE2 metabolite, 13,14-dihydro-15-keto-PGE2, was inactive at 0.1 nmole/g. For both routes of administration, PGF2 alpha appeared to be the most potent of the PGs tested. PGs administered alone by either route to unilaterally lesioned mice did not produce circling. Pretreatment with the PG synthetase inhibitor, indomethacin, caused the apo treated mice to circle at significantly higher rates than control animals. These results are the first report suggesting that within dopamine (DA)-mediated pathways PGs act at sites postsynaptic to the dopaminergic synapse.

Acute renal failure secondary to bilateral ureteric obstruction: review of 50 cases

The records of 50 patients with acute renal failure secondary to bilateral ureteric obstruction were reviewed. An underlying malignant disorder was the cause of the obstruction in 38 of the patients and had not previously been diagnosed in almost half of them. Carcinomas of the cervix and prostate were the most frequent malignant disorders, and aggressive management resulted in good survival rates. Similarly, the outcome for patients with benign bilateral ureteric obstruction, usually caused by retroperitoneal fibrosis, was good with proper management.

Prostaglandin inhibition of amphetamine-induced circling in mice

The effect of prostaglandins (PG) on amphetamine(AMPH)-induced circling was examined in mice unilaterally lesioned with 6-hydroxy-dopamine. At doses of 0.03-1.0 nmol/g, intraventricularly injected PGD2, PGE2, and PGF2 alpha all inhibited AMP-induced circling, while thromboxane-B2 (TxB2) was inactive at 1.0 nmol/g. The inhibition of circling was not due to alterations in body temperature as measured by rectal temperature changes. When injected intrastriatally, the same major PG inhibited AMP-induced circling at the lower doses of 0.01-0.1 nmol/g, while the PGE2 metabolite 13, 14-dihydro-15-keto-PGE2 was inactive at 0.1 nmol/g. PG administered alone did not procude circling. For both routes of administration, the order of potency was PGE2 greater than PGD2 greater than PGF2 alpha. These results suggest that PG can alter motor function governed by central dopaminergic pathways.

The pathogenesis of renal dysplasia. III. Complete and incomplete urinary obstruction

We graded obstructed kidneys of infants on the hypodysplasia scale to assess the influence of complete and partial obstruction on the pathogenesis of hypodysplasia. Kidneys with complete obstruction exhibited severe grades; those with partial ureteral obstruction had near normal grades. Those kidneys subjected to partial urethral obstruction ranged from mild to severe grades which correlated with degrees of lateral ectopy of the urethral office. Renal parenchymal development was impaired by complete obstruction but was tolerant to incomplete obstruction. Abnormal orifice positions associated with urethral obstructions were considered to be manifestations of ectopic ureteric buds and the hypodysplasia to be evidence of abnormal induction of abnormal renal blastema.

The pathogenesis of renal dysplasia. II. The significance of lateral and medial ectopy of the ureteric orifice

Renal hypoplasia and dysplasia may be primary malformations linked to a panureteric bud deformity or result from damage to the developing nephrons caused by abnormal urodynamic pressures, Kidneys with misplaced ureteric orifices were graded, according to histologic criteria, on the hypodysplasia scale. With lateral ectopy of the ureteric orifices with and without congenital urethral obstruction, the grades correlated with specific orifice positions. The grades of kidneys with caudal ectopy of the ureters indicated a more general correlation. Dysgenesis of the bud and nephrogenic mesenchyme may account for the renal hypodysplasia when the ureteric orifice is found to be ectopic.

The pathogenesis of renal dysplasia. I. Quantification of hypoplasia and dysplasia

In order to assess the relative effects of abnormal ureteric orifice position and abnormal urodynamics on the morphogenesis of hypoplasia and dysplasia in kidneys obtained from infants, we devised a method of quantifying the renal structures. The method was based on radial glomerular counts which ranged from zero to normal (seven to nine), a score for dysplastic structures, and the ratio of normal to abnormal tissues present. These three values, when plotted against each other, correlated closely. The glomerular count, with occasional minor adjustment for inconsistencies, was the best parameter of hypodysplasia. Severe to moderate grades of hypodysplasias fell in the low and middle ranges and hypoplasia through to normal in the highest range. By grading kidneys in this way, we were able to compare the effects of ureteral ectopy and abnormal urinary dynamics on the developing kidney.