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Biomedical subjects

E Mutschler

Publications and source records attributed to E Mutschler.

At least 91 records · Page 5Linked to original sources
PubMed1995

Beta 1-adrenoceptor subtype selective antagonism of esmolol and its major metabolite in vitro and in man. Investigations using tricresylphosphate as red blood cell carboxylesterase inhibitor.

Esmolol (CAS 103598-03-4, ASL-8052, Brevibloc) is an ultrashort acting beta-adrenoceptor antagonist which is rapidly hydrolyzed by a red blood cell esterase. In order to investigate the affinity profile of esmolol and its acid metabolite at beta-adrenoceptor subtypes in plasma and in whole blood in radioligand binding studies a potent esterase inhibitor was needed to prevent hydrolysis of esmolol and--in contrast to sodium fluoride--without influencing binding of the drugs at the receptor site. Tricresylphosphate was found to be a potent inhibitor of hydrolysis of esmolol which did not affect the parameters of radioligand binding. During an incubation time of 15 min at 25 degrees C in whole blood no significant metabolism of esmolol took place whereas without addition of inhibitor about 20% were inactivated. Thus, for the first time exact determinations of plasma concentrations of esmolol by ligand binding studies could be carried out. In vitro in radioligand binding studies esmolol had a 34 fold higher affinity for beta 1-adrenoceptors than for beta 2-adrenoceptors. Its acid metabolite had a very low and nonselective affinity for both adrenoceptor subtypes: Compared with esmolol it was 400fold less potent at beta 1-adrenoceptors. When plasma concentrations of esmolol and its metabolite after i.v. administration of esmolol to healthy volunteers (3000 micrograms/kg as a bolus and consecutively 500 micrograms/kg/min for 70 min) were determined in parallel by a beta 1-selective radioreceptor assay and an HPLC-method the following conclusions could be drawn from the direct correlation between the respective results: 1. (ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-1 Receptor Antagonists↗
PubMed1995

Investigations on the acute toxicity of acidic and basic triamterene derivatives.

Acidic and basic triamterene derivatives were evaluated with respect to their acute toxicity. After single intravenous application in mice, derivatives with a basic side-chain were much more toxic than compounds with an acidic side-chain. There is a significant correlation between the potassium retaining properties (measured as ED50) and the acute toxicity (measured as LD50) of the substances. The low acute toxicity after oral application of the compounds can be explained by their low oral bioavailability.

Animals↗
PubMed1995

Quality of cefotaxime sodium preparations.

Cefotaxime sodium (CAS 64485-93-4) is a semisynthetic cephalosporin derivative belonging to the third-generation cephalosporins. Owing to its broad antibacterial activity and its high resistance to beta-lactamases it can be used for a large variety of infections. In the present study the quality standard of 15 different cefotaxime sodium manufacturers from 9 different countries has been examined. The best results were received for the preparation Claforan. None of the 14 other products showed comparable results especially with respect to particulate matter and by-products. The particulate contamination of the 14 foreign products showed relatively high values although they still comply with the limits set by the pharmacopoeias. In contrast, in Claforan very few particles were found in the solution. This is of importance as the drug has to be administered either i.v. as an infusion or i.m. as an injection. Also the amount of by-products measured in the 14 foreign preparations was about 1.5 times higher than the one measured for Claforan. Although these are not critical results, they do indicate that there are marked differences between the quality of the products from different countries which should be taken into account.

Acetates↗
PubMed1994

Insertion mutagenesis as a tool to predict the secondary structure of a muscarinic receptor domain determining specificity of G-protein coupling.

The N-terminal segment of the third intracellular loop (i3) of muscarinic acetylcholine receptors and other G protein-coupled receptors has been shown to largely determine the G-protein coupling selectivity displayed by a given receptor subtype. Based on secondary-structure prediction algorithms, we have tested the hypothesis that this region adopts an alpha-helical secondary structure. Using the rat m3 muscarinic receptor as a model system, a series of five mutant receptors, m3(+1A) to m3(+5A) were created in which one to five additional alanine residues were inserted between the end of the fifth transmembrane domain and the beginning of i3. We speculated that this manipulation should lead to a rotation of the N-terminal segment of the i3 domain (if it is in fact alpha-helically arranged), thus producing pronounced effects on receptor/G protein coupling. Pharmacological analysis of the various mutant receptors expressed in COS-7 cells showed that m3(+1A), m3(+3A), and m3(+4A) retained strong functional activity, whereas m3(+2A) and m3(+5A) proved to be virtually inactive. Helical wheel models show that this pattern is fully consistent with the notion that the N-terminal portion of i3 forms an amphiphilic alpha-helix and that the hydrophobic side of this helix represents the G-protein recognition surface.

Acetylcholine↗
PubMed1994

Functional role in ligand binding and receptor activation of an asparagine residue present in the sixth transmembrane domain of all muscarinic acetylcholine receptors.

The molecular mechanisms through which muscarinic receptors are activated upon binding of the neurotransmitter acetylcholine (ACh) are still poorly understood. Classical structure-function relationship studies have previously established that the ACh ester moiety plays a key role in muscarinic receptor recognition and activation. Consistent with this notion, all recently proposed three-dimensional muscarinic receptor models predict that an asparagine residue present in transmembrane domain VI of all muscarinic receptors is critically involved in the binding of the ACh ester moiety by means of hydrogen bonding. To test the correctness of this hypothesis, we created several mutant m3 muscarinic receptors in which this residue (Asn507) was replaced with alanine, serine, or aspartic acid. Radioligand binding studies with transfected COS-7 cells showed that, in contrast to the predictions made based on molecular modeling studies, all three mutant receptors were able to bind ACh and the structurally related muscarinic agonist, carbachol, with high affinities which differed from the corresponding wild type values by less than 5-fold. However, all three mutations led to dramatic reductions (235-28,300-fold) in binding affinities for certain subclasses of muscarinic antagonists including atropine-like agents and pirenzepine. The m3(Asn507-->Ala) and m3(Asn507-->Asp) mutant receptors were able to mediate carbachol-induced phosphatidylinositol hydrolysis in a fashion similar to that of the wild type receptor. Interestingly, the m3(Asn507-->Ser) mutant receptor displayed about 2-fold increased basal inositol phosphate levels, raising the possibility that it is constitutively active. In conclusion, our data suggest that the asparagine residue present in transmembrane domain VI of all muscarinic receptors is not critical for ACh binding and agonist-induced receptor activation, but plays a key role in the binding of certain subclasses of muscarinic antagonists.

Acetylcholine↗
PubMed1994

Functional role of a cytoplasmic aromatic amino acid in muscarinic receptor-mediated activation of phospholipase C.

The N-terminal portion of the third intracellular loop (i3) of muscarinic acetylcholine and other G protein-coupled receptors has been shown to largely determine the G protein coupling profile of a given receptor subtype. Using the rat m3 muscarinic receptor as a model system, we have recently demonstrated that a tyrosine residue (Tyr-254), located at the beginning of the i3 domain, is critically involved in muscarinic receptor-mediated stimulation of phosphatidylinositol (PI) hydrolysis (Blüml, K., Mutschler, E., and Wess, J. (1994) J. Biol. Chem. 269, 402-405). This study was designed to investigate the functional role of this amino acid in further molecular detail. Replacement of Tyr-254 (rat m3 receptor) with alanine or exchange of its position with Ile-253 virtually abolished receptor-mediated stimulation of PI hydrolysis studied in transfected COS-7 cells. In contrast, substitution of Tyr-254 by other aromatic residues such as phenylalanine or tryptophan resulted in mutant receptors that behaved functionally similar to the wild type m3 receptor. Introduction of Tyr-254 into the corresponding position (Ser-210) of the m2 muscarinic receptor (which is only poorly coupled to PI turnover) did not result in an enhanced PI response. However, "reinsertion" of Tyr-254 into a functionally inactive chimeric m3/m2 muscarinic receptor (containing m2 receptor sequence at the N terminus of the i3 loop) yielded a mutant receptor that was able to stimulate PI hydrolysis to a similar maximum extent as the wild type m3 receptor. Taken together, our data provide strong evidence that muscarinic receptor-mediated stimulation of PI metabolism is critically dependent on the presence and proper positioning of an aromatic residue at the beginning of the i3 loop.

Amino Acid Sequence↗
PubMed1994

Identification of an intracellular tyrosine residue critical for muscarinic receptor-mediated stimulation of phosphatidylinositol hydrolysis.

Several lines of evidence suggest that the N-terminal portion of the third cytoplasmic loop (i3) of muscarinic and other G protein-coupled receptors is of pivotal importance for G protein recognition and activation. The present study was designed to identify specific amino acids within this domain required for muscarinic receptor-induced activation of G proteins mediating stimulation of phosphatidylinositol (PI) hydrolysis. Among the five mammalian muscarinic receptors (m1-m5), only the m1, m3, and m5 receptors are efficiently coupled to this second messenger pathway. Initially, we created a series of rat m3 receptor mutants in which short segments in the N terminus of the i3 loop were replaced with the corresponding m2 receptor sequences. The effect of these substitutions on m3 receptor-mediated stimulation of PI hydrolysis was studied in transiently transfected COS-7 cells. We found that a stretch of 4 amino acids (Arg252-Ile253-Tyr254-Lys255) located at the beginning of the i3 domain of the m3 muscarinic receptor is critically involved in receptor-mediated stimulation of PI hydrolysis. Further mutational analysis of this 4-amino acid segment by single amino acid substitutions demonstrated that only Tyr254 is essential for efficient activation of the PI pathway. This tyrosine residue is conserved among all PI-coupled muscarinic receptors as well as in many other biogenic amine and glycoprotein hormone receptors, suggesting that it may also play an important functional role in other G protein-coupled receptors.

Amino Acid Sequence↗
PubMed1994

Simultaneous determination of (R)- and (S)-brefanolol in human plasma: high-performance liquid chromatographic assay on a chiral stationary phase.

A new method for the quantitative enantiospecific determination of rac-brefanolol, a vasodilating beta-adrenoceptor blocking agent, in human plasma is described. After an alkaline liquid-liquid extraction from biological material and a preseparation on a silica gel column with fractional collection of the eluate, the separation of the underivatized enantiomers is performed by high-performance liquid chromatography on cellulose tris-4-methylbenzoic acid polymer coated on silica gel. The UV-absorbance of the eluate was monitored at 254 nm. Determination limits are 10 ng enantiomer per ml plasma and allow the performance of pharmacokinetic studies after the aimed therapeutic dosages.

Chromatography, High Pressure Liquid↗
PubMed1994

Characterization of the prejunctional muscarinic receptors mediating inhibition of evoked release of endogenous noradrenaline in rabbit isolated vas deferens.

The aim of the present study was to characterize the prejunctional modulation of evoked release of endogenous noradrenaline in rabbit vas deferens by the use of muscarinic receptor agonists and subtype-preferring antagonists. Vasa deferentia of the rabbit were stimulated electrically by trains of 120 pulses delivered at 4 Hz or trains of 30 pulses at 1 Hz. The inhibition by muscarinic agonists of the stimulation-evoked overflow of endogenous noradrenaline in the absence and presence of antagonists was used to determine affinity constants for antagonists. These values were compared with those observed at putative M1 receptors inhibiting neurogenic twitch contractions in the rabbit vas deferens and with affinity data obtained at M1(m1)-M4(m5) receptors in functional studies and binding experiments. The evoked overflow of noradrenaline from sympathetic nerves was enhanced by the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), the P2 purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) and indomethacin, indicating a tonic inhibition by endogenous A1 and P2 purinoceptor agonists and prostanoids, respectively. The stimulation-evoked overflow at 4 Hz was not sensitive to inhibition by the muscarinic agonists methacholine or 4-(4-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium iodide (4-Cl-McN-A-343). In contrast, at a stimulation frequency of 1 Hz the evoked noradrenaline release was decreased by muscarinic agonists (EC50): arecaidine propargyl ester (0.062 microM), 4-Cl-McN-A-343 (0.32 microM), 4-(4-fluorophenylcarbamoyloxy)-2-butynyl-N-methyl-pyrrolidinium tosylate (4-F-PyMcN+; 0.48 microM) and methacholine (0.86 microM). The affinity constants of most of the muscarinic antagonists [atropine: pKB = 9.47; (R)-trihexyphenidyl: pKB = 9.18; pirenzepine: pA2 = 7.68; methoctramine: pKB = 6.90] are consistent with estimates of these antagonists at M1(m1) receptors determined in various functional and binding studies. The high antagonistic potency of pirenzepine and (R)-trihexyphenidyl and the agonistic activity of 4-F-PyMcN+ argue for the involvement of M1, and against that of M2 and M3 receptors in the inhibition of evoked noradrenaline overflow. However, the high apparent pKB of 8.30 for himbacine is not in accordance with an M1 receptor; by contrast, it would be compatible with the presence of M2 or M4 receptors. The potencies of the tested muscarinic agonists and antagonists largely agree with those obtained for the inhibition of neurogenic twitch responses (0.05 Hz) in the rabbit vas deferens.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

The effect of ciclotropium on human heart rate.

Ciclotropium is a recently developed parasympathicolytic agent. Plasma concentration and heart rate increase (the most prominent anticholinergic effects) were measured in 12 healthy subjects before, during and after a 15-min intravenous infusion of 10 mg ciclotropium. The effect was described by using either a linear or a nonlinear (Emax) effect model linked to a linear three-compartment kinetic model via an effect compartment. Maximum heart rate increase was 33 (10) beats.min-1, and half-value duration of effect was 41 (9) min. Total plasma clearance was 0.51 (0.13) l.min-1, and mean terminal elimination half-life was 12(4) h, whereas the equilibration half-lives of drug removal from the effect compartment ranged from 2 to 14 min.

Adult↗
PubMed1994

The saluretic effect of the thiazide diuretic bemetizide in relation to the glomerular filtration rate.

The effect of the thiazide diuretic, bemetizide, on the excretion of Na+, K+, Cl-, Ca2+, and Mg2+ in relation to the glomerular filtration rate (GFR) was studied in 17 subjects whose creatinine clearances ranged from 133 to 5 ml.min-1. After a 2-day fluid and salt balanced control period, 25 mg bemetizide given orally induced natriuresis and kaliuresis which lasted for 24 h and were proportional to the GFR of the patients. The ratio of bemetizide-induced K+/Na+ excretion was always 0.17 irrespective of individual GFR. In renal failure, bemetizide increased the fractional Na+ excretion from 3% to about 10%. Kaliuresis was associated with magnesiuria, whereas bemetizide-induced calciuresis was insignificant. The thiazide reversibly lowered GFR in all subjects.

Adult↗
PubMed1994

Pharmacokinetics and pharmacodynamics of lisinopril in advanced renal failure. Consequence of dose adjustment.

To prevent drug accumulation and adverse effects the dose of hydrophilic angiotensin-converting enzyme (ACE) inhibitors, e.g. lisinopril, must be reduced in patients with renal failure. To obtain a rational basis for dose recommendations, we undertook a prospective clinical trial. After 15 days of lisinopril treatment pharmacokinetic and pharmacodynamic parameters were determined in patients with advanced renal failure (n = 8; endogenous creatinine clearance [CLCR]: 18 ml.min-1.1.73 m-2) and in healthy subjects with normal renal function (n = 16; CLCR: 107 ml.min-1.1.73 m-2). The volunteers received 10 mg lisinopril once daily, the daily dose in patients (1.1-2.2 mg) was adjusted to the individual CLCR according to the method of Dettli [13]. After 15 days of lisinopril treatment the mean maximal serum concentration (Cmax) in patients was lower than in volunteers (30.7 vs 40.7 ng.ml-1, while the mean area under the concentration-time curve (AUC0-24 h) was higher (525 vs 473 ng.h-1.ml-1). ACE activity on day 15 was almost completely inhibited in both groups. Plasma renin activity, angiotensin I and angiotensin II levels documented marked inhibition of converting enzyme in volunteers and patients. Furthermore, average mean arterial blood pressure in patients decreased by 5 mmHg and proteinuria from 3.9-2.7 g per 24 h after 15 days of treatment with the reduced dose of lisinopril. Adjustment of the dose of lisinopril prevents significant accumulation of the drug in patients with advanced renal failure during chronic therapy. Mean serum levels did not exceed this in subjects with normal renal function receiving a standard dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Predictions of in vivo plasma concentrations from in vitro release kinetics: application to doxepin parenteral (i.m.) suspensions in lipophilic vehicles in dogs.

A flow through dissolution system was applied to obtain biorelevant dissolution rates from controlled release systems for parenteral administration using the antidepressant doxepin as a model compound. Plasma concentrations were simulated using the disposition function of doxepin obtained from administration of an aqueous doxepin solution (AponalR) to beagle dogs. Input functions were obtained from in vitro dissolution experiments with three parenteral controlled release suspensions of doxepin hydrochloride (DHCl), doxepin pamoate (DP-1), and microspheres of doxepin hydrochloride in poly D,L-lactid-co-glycolid (MC-1) in isopropyl myristate. The predicted plasma concentrations were compared with experimentally obtained concentrations in vivo. Good correlations (r > 0.88) between observed and predicted data were obtained for all formulations investigated. Similarly, in vivo release kinetics calculated by the Loo-Riegelman method were compard with release kinetics measured in vitro and showed good correlations (r > 0.89). It is anticipated that the in vitro dissolution system permits assessment of the clinical relevance of observed variations in dissolution rates e.g. between batches of one formulation.

Absorption↗
PubMed1994

Pharmacokinetic and pharmacodynamic aspects of an ophthalmic pilocarpine nanoparticle-delivery-system.

The regional pharmacokinetics as well as the pharmacodynamics of pilocarpine-loaded nanoparticles for the treatment of glaucoma were investigated and compared to a solution of this drug. Polybutylcyanoacrylate nanoparticles were prepared by an emulsion polymerization process. Formulations with different drug concentrations (2-6%) as well as different particle concentrations were investigated and analyzed for size and drug loading. Drug binding to the particles was achieved at a level of 10-18% of the total drug content. The colloidal nanoparticles were sufficiently small (diameter: 100-300 nm) for a non-irritating application to the eye. All preparations were applied to the eyes of New Zealand white rabbits which were treated with betamethasone before to create an elevated intraocular pressure (IOP). Pilocarpine concentrations, assayed from aqueous humor using gaschromatography, increased by 23% (AUC) for nanoparticle suspensions compared to aqueous reference solutions. Additionally, t1/2 was prolonged and the elimination coefficient was significantly decreased. Pharmacodynamic effects such as miosis and IOP reduction were investigated. tmax values of aqueous humor concentration were observed to be in a similar time range as miosis tmax readings. It was found that at lower drug contents a more pronounced prolongation of miosis was achieved with nanoparticles versus a standard solution. The IOP-reduction was significantly prolonged with nanoparticles preparations; whereas maximum reduction was obtained with a reference solution after 1-2 hours, it was reached with nanoparticles at about 2-3 hours. Differences between nanoparticles and aqueous solutions were most pronounced at lower drug concentrations.

Animals↗
PubMed1994

Alinidine prevents hypoperfusion-induced transmural flow redistribution in isolated paced rat hearts.

1. The effect of alinidine on transmural flow redistribution during hypoperfusion was studied in the isolated rat heart. 2. Low flow perfusion of paced (5 Hz) rat Langendorff preparations with Tyrode's solution for 60 min resulted in loss of left ventricular pressure amplitude and contracture. 3. In the presence of 45.6 mumol/L alinidine in the hypoperfusion medium contractility was maintained and contracture was missing. 4. Myocardial sphere densities were assessed by infusion of fluorescent microspheres after 60 min of hypoperfusion. Histomorphometric evaluation of the left ventricular wall indicated marked redistribution of myocardial flow to the epicardium. Endo/epicardial quotients of sphere densities were significantly greater in alinidine-treated hearts. 5. Perfusion of hearts with 45.6 mumol/L alinidine for 30 min at a pressure of 80 cmH2O decreased coronary flow and contractility, but did not change the transmural quotient of sphere densities. 6. These results show that in isolated rat hearts with a ventricular wall of only 3-4 mm thickness severe hypoperfusion induces a shift in transmural flow distribution which is prevented by alinidine.

Animals↗
PubMed1994

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.

Animals↗