Metrifonate and tacrine: a comparative study on their effect on acetylcholine dynamics in mouse brain

Tetrahydroaminoacridine (THA) and metrifonate are cholinesterase inhibitors used in the treatment of Alzheimer's disease. In experimental animals they inhibit acetylcholinesterase activity and have been reported to increase levels of brain acetylcholine. This paper presents results from studies of their effect at two dose levels on the dynamics of acetylcholine in mouse brain. Metrifonate at two doses (10 and 30 mg/kg intraperitoneally), known to cause cholinesterase inhibition, had no effect on levels of acetylcholine or choline or on the rate of synthesis of acetylcholine. THA (3 mg/kg intraperitoneally) had no effect on levels of acetylcholine and choline but had a shortlasting decreasing effect on the synthesis rate of acetylcholine. THA (10 mg/kg intraperitoneally) increased levels of acetylcholine and choline and markedly decreased the synthesis rate of acetylcholine. At this dose, the animals showed severe cholinergic effects, e.g. tremor and salivation. It is suggested that a moderate cholinesterase inhibition in brain facilitates cholinergic nerve transmission which is obtained at a broader dose range for metrifonate than for THA.

Intoxications with anticholinesterases: effect of different combinations of antidotes on the dynamics of acetylcholine in mouse brain

Intoxications with organophosphorus compounds are normally treated with a mixture of atropine and an enzyme regenerating oxime. The addition of diazepam to the conventional drug therapy is reported to greatly improve the antidotal effect. The implication of the cholinergic system in such intoxications prompted us to study the effect of different combinations of antidotes on the acetylcholine (ACh) synthesizing system in mouse brain in vivo. The antidotes studied in this paper are diazepam, HI-6 and 1-hyoscyamine, the active enantiomer of atropine. Diazepam decreases the synthesis rate of ACh both when administered separately and in combination with 1-hyoscyamine and HI-6. This is in contrast to 1-hyoscyamine which, in addition to blocking muscarinic receptors, also increases the release and rate of synthesis of ACh, which probably is an unfavourable effect of the antidote. This might at least partly explain the advantage of combining 1-hyoscyamine and an oxime with diazepam in intoxications with anticholinesterases. Mice administered soman (0.75 x LD50), after pretreatment with the three-drug combination of antidotes, show no cholinergic symptoms despite a 50% increase in endogenous ACh. The rate of synthesis of ACh in these mice is in the same range as in animals administered diazepam alone. Mice administered the same dose of soman with no antidotal pretreatment suffer from severe tremor and salivation, and have a strongly reduced synthesis rate of ACh.

Effects of diazepam on muscarinic acetylcholine receptor binding in vivo and on oxotremorine-induced tremor and hypothermia in mice

Diazepam has previously been shown to affect the acetylcholine synthesizing system in mouse brain. This paper reports studies on the effect of diazepam on muscarinic receptor density and on pharmacological effects of oxotremorine. The receptor density was studied using a new technique that allows such studies to be performed in vivo under physiological conditions. The method is based on the fact that L-hyoscyamine, the active antipode of atropine, binds specifically to muscarinic receptors in the brain, and can be measured with high sensitivity by gas chromatography--mass spectrometry. Diazepam was found to modify the binding properties of muscarinic receptors in CNS, thereby decreasing the functional receptor pool. It also prevented tremor induced by the muscarinic agonist oxotremorine. Diazepam could however not prevent the hypothermia induced, but rather accentuated this effect of oxotremorine. It is concluded that diazepam, directly or indirectly, influences the effect of cholinergic stimulators by modulating the size of the muscarinic receptor pool.

Effects of diazepam on blood choline and acetylcholine turnover in brain of mice

The effect of diazepam on the acetylcholine (ACh) synthesizing system has been studied in mouse brain in vivo. ACh and choline (Ch) were analyzed by gas chromatography - mass spectrometry using deuterated internal standards. Turnover of ACh was studied by following the incorporation of Ch into ACh after an intravenous injection of [2H6]-Ch. The mice were killed by focussed microwave irradiation on the head. Diazepam was found to increase the endogenous level of Ch, while the concentration of [2H6]-Ch was only half of that of the controls. The incorporation of [2H6]-Ch into [2H6]-ACh was decreased, while the endogenous level of ACh was slightly increased. The turnover rate of ACh was decreased, consistent with a decrease in neuronal excitability induced by diazepam. The elevated endogenous Ch-level and the lower concentration of [2H6]-Ch in the brain, might be explained by an effect of diazepam on the Ch-transport across the blood-brain barrier. This theory is supported by experiments where levels of endogenous and [2H6]-labelled Ch were analyzed in blood following an intravenous injection of [2H6]-Ch. The [2H6]-Ch was found to be eliminated faster in blood from diazepam treated mice. The increased blood level of endogenous Ch, induced by the [2H6]-Ch injection also returned more rapidly to normal in these animals. This is consistent with peripheral Ch being eliminated faster when the central Ch supply is decreased.

A method using L-hyoscyamine for the study of muscarinic acetylcholine receptor binding in vivo

Studies of muscarinic receptor concentration and comparative binding assays of agonists and antagonists are presently done in vitro by incubation and measurement of the binding to tissue homogenates of the radiolabelled potent antagonists 3H-scopolamine or 3H-quinuclidinyl benzilate. We have developed a technique based on gas chromatography-mass spectrometry that allows studies of the muscarinic receptor concentration to be performed in vivo under physiologic conditions. By injecting the optical antipodes of atropine, D- and L-hyoscyamine separately in mice and following their kinetics in different parts of the brain it was possible to separate the specific receptor binding of the active antipode L-hyoscyamine from that of the inactive antipode D-hyoscyamine, representing unspecific binding. Two hrs after the administration of L-hyoscyamine, 2 mg/kg intravenously, its concentration in brain was found to represent "maximum" specific binding. The physiological significance of specifically bound L-hyoscyamine was tested on its blocking effect on oxotremorine induced tremor.

Distribution and elimination of the stereoisomers of soman and their effect on brain acetylcholine

The four stereoisomers of soman (O-(1,2,2-trimethylpropyl)-methyl-fluorophosphonate) have been analyzed in vivo in mouse blood and tissues after administration of doses corresponding to 0.75 X LD50 of the two diastereoisomeric pairs of soman (Sc- and Rc-soman). The disappearance of the four isomers has been studied in vitro in the presence of enzymes involved in the toxicity and detoxification of soman, e.g., acetyl- and pseudocholinesterase, aliesterase, and phosphorylphosphatase. The effect of Sc- and Rc-soman on brain acetylcholine was studied in the mouse. The analytical methods used are based on gas chromatography-mass spectrometry with deuterated internal standards. Rc-Rp- and ScRp-soman, the two isomers that preferentially react with acetylcholinesterase, were found in blood and liver. In liver the concentration of ScRp was higher than that of RcRp and could be followed for 18 hr. In blood only ScRp could be found. Its presence there could be followed during 18 hr. The levels were, however, lower than in liver. The results indicate that the liver might be a depot for soman and that ScRp might be responsible for the delayed intoxication noted after treatment with antidotes. Rc-soman was found to have a more pronounced effect on the acetylcholine synthesizing system than has Sc-soman, which might explain its higher in vivo toxicity.

Stereoselectivity of muscarinic receptors in vivo and in vitro for oxotremorine analogues. N-[4-(tertiary amino)-2-butynyl]-5-methyl-2-pyrrolidones

The enantiomers of three 5-methyl-2-pyrrolidone analogues of the muscarinic agent oxotremorine (1) were synthesized. The pyrrolidine derivative (R)-13 was an antagonist to carbachol in the guinea pig ileum and also showed central and peripheral antimuscarinic activity in vivo. It was more potent and more selective than atropine in antagonizing the central effects of 1. The dimethylamino analogue (R)-14 and the trimethylammonium salt (R)-15 were potent agonists in the guinea pig ileum. (R)-14 showed both central muscarinic (hypothermia) and central antimuscarinic activity (antagonism of oxotremorine-induced tremor) in vivo. The R enantiomers of 13-15 were considerably more potent than the S enantiomers in vivo and in vitro irrespective of whether agonist or antagonist activity was measured. From a comparison of the contribution of the methyl group at the chiral center to the overall affinities, it is suggested that agonists and antagonists in this series bind in an essentially identical manner to the muscarinic receptor.

Pharmacokinetics of terodiline in human volunteers

The pharmacokinetics of terodiline HCl was studied in nine healthy volunteers given 12.5 mg i.v. and p.o. or 20 mg i.v. and 25 mg p.o. on two different occasions. The serum concentrations were measured by gas chromatography--mas spectrometry, using deuterated terodiline HCl as the internal standard. After i.v. administration the kinetics could be described by a two-compartment model with a mean distribution half life of 0.3 h and a mean elimination half life of 63 h. The serum clearance and apparent volume of distribution varied about 4-fold with mean values of 4.8 1/h and 417 1, respectively. After oral administration, the mean half life of absorption was 0.7 h and that of elimination 65 h. The absolute bioavailability varied between 64% and 105% with a mean of 92%. The long serum half life of terodiline should permit its once daily administration.

Atropine in mouse brain and plasma quantified by mass fragmentography

A gas chromatography - mass spectrometric method has been developed for the assay of atropine in blood and brain tissue samples of mice. The method is based on the use of deuterium labelled atropine as internal standard and has a sensitivity allowing analyses of small brain structures, e.g. striatum and hippocampus. The method has been used to study the distribution and disposition of atropine in blood and brain of mice. The data obtained in blood can best be fitted by a two compartment open model with the elimination half-life of about 100 min., which was similar to that in brain. The concentration in brain structures with different cholinergic neuronal density was about the same.

Metabolism of lidocaine in human liver in vitro

We have incubated the local anaesthetic drug lidocaine with microsomes from human adult livers. The metabolites deethylated lidocaine (MEGX) and aromatically hydroxylated lidocaine (3-hydroxylidocaine) were isolated by high performance liquid chromatography and quantitated by the liquid scintillation counting technique. The deethylation rate markedly exceeded the hydroxylation rate also at very low lidocaine concentrations. This pattern differs from that detected earlier with rat liver microsomes where aromatic hydroxylation is significant at low lidocaine concentrations, but it is similar to that in female guinea pig microsomes. These findings show the importance of performing this type of experiments also with human materials.

Absorption of boron after mouthwash treatment with Bocosept

Healthy volunteers and patients with gingivitis were treated locally with the boron-containing bacteriostatic agent, Bocosept. Blood levels and urinary excretion of boron were examined by a spectrophotometric method. Blood concentrations after a single mouthwash with Bocosept slightly exceeded those after intake of 200 g raisins or a bottle of red wine. The blood levels during a one-week course of treatment showed a low rate of boron accumulation. The highest concentration was about 0.3 microgram B/ml, a level which does not seem to involve any risk of boron poisoning. The small amount taken up after mouthwash treatment with Bocosept does not appear to represent absorption by the oral mucosa. It seems more likely that the uptake of boron takes place in the intestine after ingestion of residual amounts from the mouth.

Effect of physostigmine and atropine on acetylcholine turnover in mouse brain

The effect of physostigmine salicylate (0.5 mg/kg, i.p.) alone and in combination with atropine sulfate (25 mg/kg, i.p.) on levels of acetylcholine (ACh) and choline (Ch) and turnover of ACh has been studied in whole brain and striatum of mice. The animals were killed by focussed microwave irradiation and the turnover of ACh was studied after i.v. injection of deuterium labelled Ch by employing mass fragmentography. Physostigmine increased the levels of ACh in whole brain from 24.5--28.0 nmol/g(P less than 0.001) whereas there was no significant increase in striatum. The levels of Ch were also increased. The turnover rate of ACh was decreased in whole brain from 15.4 to 8.4 and in striatum from 52.9 to 24.4 nmol/g . min. Physostigmine given before or after atropine did not completely block the ACh lowering effect of atropine. When atropine was given before physostigmine the turnover rate of ACh in whole brain was increased to 24.2 nmoles/g . min. The results seem to indicate that there is no clear cut relation between the turnover rate and level of ACh in vivo. The increase of the turnover rate induced by atropine is masked unless a cholinesterase inhibitor is given to protect the newly synthesized labelled ACh released by atropine.

Evidence for two catalytically different binding sites of liver microsomal cytochrome P-450: importance for species and sex differences in oxidation pattern of lidocaine

When the local anaesthetic drug lidocaine is added to liver microsomes biphasic type I spectral change titration curves can be observed. A high-affinity and a low-affinity phase is observed. In the present study we have found that microsomes from female rats have a dominant high-affinity phase, which can hardly be observed within microsomes from female guinea pigs. Male rats showed an intermediate phase. On incubation of lidocaine at concentrations of 1 micron or less with female rat liver microsomes a larger fraction of the drug was aromatically hydroxylated than deethylated. The opposite was true for guinea pig liver microsomes, and microsomes from male rats were intermediate. The ratio between the formation of deethylated and hydroxylated metabolites increased with the lidocaine concentration and at a lidocaine concentration of 10(-4)M deethylation was the dominant oxidation type in all microsomes. The data suggest that the two spectral phases represent two binding sites of cytochrome P-450 each having a certain "catalytic specificity" - the high affinity catalyzing aromatic hydroxylation and the "low-affinity site" deethylation. This hypothesis is further supported by the observed differential effects of pH and MgCl2 concentration on the two types of oxidation.

Extraction and metabolism of lidocaine in rat liver

The use of lidocaine as an oral antiarrhythmic drug is limited by its rapid disposition in the liver. In accordance with this we found that the drug was completely extracted during one passage through the perfused rat liver. The drug binds to rat liver microsomes with a type I spectral change of unusually high affinity. It is rapidly de-ethylated by the microsomes with an apparent Vmax of about 15 nmol per mg protein x min. The apparent Km for this reaction is about 250 muM. The reaction occures at about the same rate in isolated rat liver cells. We believe that the high affinity of lidocaine for the cytochrome P-450 system, as indicated by its type I spectral change, as well as the rapid oxidation of the drug are the two main determinants for the marked liver extraction and first pass effect of the drug.

Assay of the major (4-hydroxylated) metabolites of diphenylhydantoin in human urine

A modified gas chromatographic procedure for the determination of unconjugated and conjugated 4-hydroxydiphenylhydantoin (4-OH-DPH) in urine has been developed. Unconjugated 4-OH-DPH is determined after selective extraction with toluene-ether (1:1). For the assay of conjugated 4-OH-DPH, the urine is pre-extracted with isoamylalcohol before acid hydrolysis to avoid interference by the dihydrodiol metabolite of DPH. The sensitivity of the method is 0.1 mug per ml. The method has been used to determine the urinary metabolites in two adult volunteers, during steady state plasma concentrations of DPH and in the elimination phase.

Synthesis and pharmacology of 1-(2-thioxopyrrolidino)-4-pyrrolidino-2-butyne, the thiolactam analogue of oxotremorine

The thiolactam analogue of oxotremorine (I) has been prepared and examined for muscarinic activity in mice and on guinea-pig ileal preparations. It is inactive in itself, but is transformed in vivo to oxotremorine (II), which has been identified in the urine of mice. The urine also contains 1-(2-oxopyrrolidino)-4-pyrrolidino-2-butanone (III) which is formed non-enzymatically from I under acidic conditions, but does not display any acetylcholine-like properties in vivo or in vitro. Oxotremorine is not formed from I in vitro.

Decreased distribution of oxotremorine to brain after pharmacological blockade of its peripheral acetylcholine-like effects

The distribution of [3H]oxotremorine, after intravenous injection, to brain and tissues of rats and mice has been studied. In rats, oxotremorine (0·3 mg/kg) rapidly reached the brain with a peak concentration of 1200 ng/g at 1 min. Blockade of the peripheral muscarinic effects of oxotremorine with amitriptyline methyl iodide or atropine methyl nitrate (25 mg/kg, s.c.) markedly decreased the brain content of oxotremorine (peak concentration 400 ng/g), probably as a result of its more rapid distribution to peripheral tissues and an increased volume of distribution. The ratio of drug distribution between plasma and brain is unaffected by pretreatment with anticholinoceptive drugs. Also, the total body concentrations of oxotremorine are similar in pretreated rats and controls. A small dose of oxotremorine (10 μg/kg) is distributed similarly in pretreated rats (amitriptyline methyl iodide, 25 mg/kg, s.c.) and in controls. In mice there was a linear relation between dose, up to 180 μg/kg, and brain concentration of oxotremorine. At higher doses, relatively; more drug reached the brain. Oxotremorine induced a marked fall in blood pressure in the unanaesthetized rat that was reduced by amitriptyline methyl iodide and reversed by atropine methyl nitrate. It seems likely that differences in blood flow between pretreated rats and controls are responsible for the differences in the distribution of the drug.