Absorption and metabolism of procaine by the rat small intestine.

The aim of this study was to obtain information about the absorption of procaine in the rat small intestine (Fisher-Parsons preparation). In the range from 0.25-10 mmol.l-1 procaine in the luminal perfusate, much more of the unchanged drug was absorbed in segments of the ileum than of the duodenum and jejunum. Besides procaine, two metabolites, p-aminobenzoic acid (PABA) and acetylated p-aminobenzoic acid (AABA), formed in the intestinal mucosa, appeared in the absorbate. With increasing substrate concentration in the perfusate the PABA in the absorbate increased considerably in all three segments; from 0.75 mmol.l-1 procaine upwards the PABA produced was highest in the jejunum. AABA formed in the mucosa and measured in the absorbate did not increase in the same manner with increasing substrate concentration; in the absorbate of jejunal segments the amount of AABA was significantly higher than in duodenal and ileal segments. Taking into account that in rats the microclimate of the ileum differs considerably from that of the upper part of the small intestine, the marked difference observed in the absorption of procaine between ileal segments on the one side, and duodenal and jejunal segments on the other, can be explained on the basis of the "non-ionic diffusion" theory.

The effect of aniline derivatives on absorption of fluid, glucose and sodium in isolated duodenal segments from rats.

Paracetamol (5-15 mmol X l-1), phenacetin (1-3 mmol X l-1) and acetanilide (5-20 mmol X l-1) enhanced fluid, glucose and sodium absorption of isolated duodenal segments from rats. In a high concentration paracetamol (30 mmol X l-1) and acetanilide (25 mmol X l-1) inhibited these parameters. The coupling coefficient of 2:1 in sodium-glucose cotransport was not changed under the influence of the aniline derivatives. Phlorizin (10(-5) mol X l-1) completely abolished the stimulatory effect of these drugs. Also in presence of 3-O-methylglucose instead of glucose in the perfusion medium a paracetamol dependent increase in fluid absorption was seen, whereas the absorption of mannitol was unchanged. The results suggest, that the increase in sodium and fluid absorption caused by aniline derivatives is due to the stimulation of active glucose transport. A cytotoxic effect may explain the decrease of absorption at high concentrations of these substances.

Sensitive HPLC assay for thiopental in human serum after simple preparation of the samples. Its application for clinical research.

A simple, precise and sensitive micro method for the determination of thiopental in human serum is presented. After deproteinization with acetonitrile the supernatant was directly injected into a reversed phase HPLC system with UV photometrical detection at 280 nm. The limit for the detection of thiopental was less than 0.1 microgram/ml serum. Time consuming extraction of the serum sample was not necessary. The method can be recommended for clinical routine analysis; its suitability has been demonstrated in several studies.

Binding of thiopental to human serum albumin in the presence of halogenated hydrocarbons and ethers.

Thiopental binding (substrate concentration 0.04.10(-3) M = 10 micrograms/ml) to 1% human serum albumin (HSA) studied by equilibrium dialysis in 1/15 M phosphate buffer solution (pH 7.4) was increased significantly from 40.2% (= control) to 55% in the presence of 4.71.10(-3) M halothane (= 11.36 vol%); 1.18.10(-3) M = 2.84 vol% halothane caused a lesser but still significant increase (vs. control) of thiopental binding. This halothane effect on the binding of thiopental to HSA was studied under several experimental conditions (variation of thiopental concentration, HSA concentration, pH of the buffer solution, temperature). Other halogenated hydrocarbons such as chloroform (6.2.10(-3) M) and carbon tetrachloride (5.2.10(-3) M) also markedly increased the binding of thiopental to HSA as compared to the control (percentage of fraction bound, 53 and 61%, respectively); the same effect, but to a lesser extent, was obtained under the influence of three halogenated ethers, i.e., enflurane (4.1.10(-3) M--greater than 45% thiopental bound), isoflurane (4.1.10(-3) M--greater than 50% bound) and methoxyflurane (4.3.10(-3) M--greater than 47% bound). Under the same experimental conditions, ethanol (up to 8.9.10(-2) M) and diethylether (up to 4.9.10(-2) M) did not increase the percentage of thiopental bound to HSA.

HPLC assay for atropine in serum and protein solutions after in vitro addition of the tropane alkaloid.

A simple and sensitive method for the determination of atropine in serum and protein solutions is presented. Atropine and procaine (internal standard) were extracted with diethylether from protein containing solutions after alkalinization. The residue of the evaporized ether phase, redissolved in diluted sulfuric acid, was injected directly onto a LiChrosorbR column. Atropine, procaine and serum constituents were separated by HPLC using an ion-pair containing mobile phase. The limit for the detection of atropine was 200 ng/ml. The method was used for the determination of atropine in a binding study. Percent binding values to human serum, human serum albumin and human alpha 1-acid glycoprotein were evaluated by equilibrium dialysis.

pH-dependent interaction of halothane upon thiopental binding to human serum albumin.

At pH 7.4 the binding of thiopental to human serum albumin (HSA) was increased in the presence of halothane. In order to obtain information about the mechanism of this interaction, in vitro binding experiments by means of equilibrium dialysis were carried out at different pH values. At pH 4.97 the binding of thiopental to HSA 1% was low (23% bound) and not influenced by halothane. An increase of thiopental binding caused by halothane could be seen at pH 7.4 (55% bound vs. 41% in the control = without halothane) and at pH 8.23 (62% vs. 54%). At pH 10.15 an opposite interaction was found: in the presence of halothane thiopental binding was considerably decreased (36.2% vs. 47.0% in the control). Evaluation of the binding parameters of experiments using increasing substrate concentrations (Scatchard plot) revealed quite different changes of the two classes of binding sites of HSA for thiopental. It is assumed that halothane causes reversible conformational changes of the albumin molecule resulting in altered binding characteristics for thiopental.

Increase of thiopental concentration in rat tissues due to anesthesia with isoflurane.

Thiopental distribution was studied in rats (30 mg/kg i.v.) anesthetized simultaneously with 1.25 "rat"-MAC isoflurane. The thiopental concentration in serum and several tissues was determined UV-photometrically at 305 nm after extraction and TLC. In the serum of rats anesthetized with isoflurane the thiopental concentration was significantly increased to +39----+74% in comparison to controls during 30 min following the barbiturate injection. Also in liver, brain, heart, kidney, lung and spleen of rats anesthetized with isoflurane the thiopental concentration was significantly increased at 3 and 10 min; at 30 min the difference vs. control had vanished in brain, heart, lung and spleen. Obviously, thiopental was transiently "trapped" during the early distribution phase to a considerable amount in these vessel-rich tissues when anesthesia with isoflurane was simultaneously performed; this pharmacokinetic interaction might be explained at least to some extent hemodynamically; in many tissues regional blood flow is reduced during anesthesia with isoflurane; thereby the "washout" of thiopental from the tissues and the redistribution are delayed.

Cardiac output and liver blood flow in humans: effect of the volatile anesthetic halothane.

In 40 men with normal circulatory and liver function, from whom 10 were undergoing general anesthesia with halothane for minor orthopedic surgery, the relationship between hemodynamic parameters and total hepatic blood flow (HBF) was investigated. Cardiac output (CO) was measured noninvasively by means of the thoracic electrical bioimpedance method, systemic arterial blood pressure (BPsys, BPdia, mean arterial pressure) by an automated oscillometric device and HBF by indocyanine green clearance. In the subjects without halothane anesthesia no relationship was found between BP and HBF, but a significant correlation could be seen between CO and HBF, whereby the fraction of HBF decreased with increasing CO. In contrast, in the presence of halothane the systemic arterial blood pressure correlated with the HBF, indicating a loss of autoregulation of the liver circulation.

Interactions between thiopental and volatile anesthetics (halothane and isoflurane) in isolated heart preparations of the rat.

Thiopental uptake into heart muscle tissue was studied in spontaneously beating rat hearts (Langendorff preparation, 0.13-0.27 mmol/l thiopental in the perfusion fluid). Up to 0.19 mmol/l the concentration of thiopental in heart muscle tissue was increased vs. control when halothane (0.8 vol%) was present. Using a constant thiopental concentration (0.13 mmol/l) and 0.8, 1.5 or 2.0 vol% halothane +12%, +29% or +43% more thiopental was taken up into heart muscle tissue compared to the control. This increased uptake was not seen in the presence of 1.2 and 2.0 vol% isoflurane. Frequency of right rat atria was decreased by increasing thiopental concentrations (0.02-0.23 mmol/l in the incubation medium). Halothane (0.8 and 1.5 vol%) and isoflurane (1.0 and 2.0 vol%) alone had no influence on frequency of right atria. Both volatile anesthetics additionally increased the negative chronotropic action of thiopental when the corresponding higher concentration was applied. Contractile force of left rat atria was decreased concentration-dependently by thiopental (0.02-0.23 mmol/l). Halothane and isoflurane alone decreased contractility. Dependent on the concentration used, both volatile anesthetics further increased the negative inotropic action of thiopental, yet preferentially at higher barbiturate concentrations.

Influence of disulfiram, diethyldithiocarbamate and carbon disulfide on the metabolic formation of trifluoroacetic acid from halothane in the rat.

Halothane (H), 2-bromo-2-chloro-1,1,1-trifluoroethane, was metabolized to trifluoroacetic acid (TFAA) over a very long time (several days) in rats after a 1 h exposure to the inhalational anesthetic. H inhibited its own metabolism as long as anesthetically active concentrations existed in the serum and tissue. That fraction of H which was not exhaled rapidly by the lung after the anesthesia was metabolized mainly over the time range from 5-48 h: 68% of the total amount of TFAA eliminated in the urine during 144 h (about 4 mg) were found in this time period. Disulfiram (D) dose dependently inhibited the formation of TFAA from H in vivo and in vitro, in liver microsomes of phenobarbital treated rats. Diethyldithiocarbamate (DDTC) and carbon disulfide (CS2), two metabolites of D, given to rats immediately after the H-anesthesia also reduced the metabolic formation of TFAA. However, if DDTC and CS2 were given 24 h before the anesthesia they caused only a small decrease in serum TFAA concentration. This finding indicates that both metabolites of D have only short-lasting inhibitory effects. In contrast, the inhibition of the oxidative metabolism of H by D seems to persist over a long time, since a small but significant decrease in the serum TFAA concentration was found even if D was given 72 h before the H-anesthesia. It was concluded that in vivo CS2 is really the active inhibitor. The short-lasting inhibitory effect of DDTC may be explained by its fast metabolic transformation into CS2, whereas the long-lasting effect of D is caused by its delayed degradation into this metabolite.

The volatile anesthetics, halothane, enflurane and isoflurane, influence the distribution of thiopental in man differently.

In man, a change of thiopental pharmacokinetics was observed under halothane anesthesia, but not when patients were anesthetized with enflurane and isoflurane. After an initial subanesthetic dose of 50 mg thiopental, the concentrations in serum (T) were determined over 15 min (4 samples). From these T-values the pharmacokinetic parameters Vc (central volume of distribution), t1/2 alpha and Cl were established (control). 16 min after the first thiopental dose, one of the inhalation anesthetics was administered (randomized). After 45 min exposure to the respective inhalation anesthetic (2-3 MAC in combination with N2O, steady-state a second dose of 50 mg thiopental was injected and the T-values were determined again over 15 min. The T-values of the control course varied considerably; the logarithmic frequency distribution revealed two distinct subgroups of patients, A and B, with characteristic Vc and t1/2 alpha. Both subgroups were influenced by the volatile anesthetics in a similar way with regard to pharmacokinetic parameters. With halothane, Vc was decreased and t1/2 alpha was shortened. In contrast, enflurane and isoflurane did not affect the pharmacokinetic parameters.

[Drug distribution during convulsive seizure in comparison with narcosis]. / Uber das Zustandekommen einer differenten Stoffverteilung während des Krampfes im Vergleich zur Narkose.

3 min after simultaneous i.v. administration of phenazone (200 mg/kg) and of pentetrazole (50 mg/kg) or of phenazone and of the convulsively active S-(+)-1-methyl-5-phenyl-5-propyl barbituric acid = (+)-MPPB (75 mg/kg), respectively, phenazone concentrations in liver, spleen and fat tissue of rats are lower, in brain tissue, however, it is higher than those of the control (rats receiving phenazone only); the distribution pattern of (+)-MPPB between the tissues corresponds to that of phenazone after simultaneous administration of pentetrazole. In rats anaesthetized by hexobarbital (35 mg/kg) or by the anaesthetically active R-(-)- 1-methyl-5-phenyl-5-propyl barbituric acid = (-)-MPPB (75 mg/kg), respectively, phenazone tissue distribution is at the same time (3 min) not different from that of the control; the tissue distribution pattern of (-)-MPPB corresponds to that of phenazone after simultaneous administration of hexobarbital. Following pretreatment with diazepam, reserpine and phenoxybenzamine, respectively, the tissue distribution pattern of (+)-MPPB, in the rats approaches that of (-)-MPPB. The distribution of (-)-MPPB in the tissues corresponds to that of (+)-MPPB, if the animals receive simultaneously pentetrazole or are electrically stimulated, respectively, to cause a convulsive seizure.

Stereoselective binding of the enantiomers of four closely related N-methyl-barbiturates to human, bovine, and rat serum albumin.

Albumin binding for the enantiomers of four closely related N-methyl-5-phenyl-5-alkyl-barbiturates 1-4 was investigated for three different mammalian species by means of equilibrium dialysis. Lipid solubility (n-heptane/phosphate buffer distribution coefficient) increased stepwise by a factor of 56 from 1 to 4. Bovine serum albumin: The (S)-(+)-enantiomers of 1-4 were bound in a higher percentage than the (R)-(-)-enantiomers; lengthening of the aliphatic side-chain increased the binding extent in both enantiomeric groups. Human serum albumin: Binding of (S)-(+)-1 and (S)-(+)-4 was higher than that of the (R)-(-)-enantiomers; with (S)-(+)-2 and (S)-(+)-3 it was much lower than that of the corresponding (R)-(-)-enantiomers. Lengthening of the aliphatic side chain increased the binding extent of the (S)-(+)- as well as the (R)-(-)-enantiomers, but with two exceptions: 1. The (S)-(+)-1 binding exceeded that of the (S)-(+)-2 by a factor of nearly two. 2. The binding extent of (R)-(-)-4 was not further increased in comparison to (R)-(-)-3. Rat serum albumin: (S)-(+)-1 and (S)-(+)-2 were bound in a lower percentage than the (R)-(-)-enantiomers, both 3-enantiomers showing an equal binding extent; (S)-(+)-4 was bound to a slightly greater extent than the (R)-(-)-4. In the group of the (S)-(+)-enantiomers, the binding extent increased from 1 to 4, whereas in that of the (R)-(-)-enantiomers only between 1 and 4. Structural differences between the serum albumins of three mammalian species possibly cause the enantioselective binding pattern found for the enantiomers of 1-4, and are responsible for the finding that the binding extent in some cases did not correlate with the lipid solubility of the compounds.

[Optically active barbiturates. Synthesis, configuration and pharmacological effects (author's transl)]. / Optisch aktive Barbituarte. Synthese, Konfiguration und pharmakologische Wirkung.

Optically active N-alkylated barbiturates are synthesized from disubstituted cyanoacetates. The configuration of the synthesized compounds is determined by chemical and chiroptical procedures and by X-ray analysis. In animals the barbiturates show a different anesthetic activity, in some cases the CNS activity is opposed, one enantiomer is anesthetically active, the other is a convulsive agent. In their pharmacokinetic behaviour the enantiomers show remarkable differences.

Thiopental binding to human serum albumin in the presence of halothane.

In vitro thiopental binding (substrate concentration 0.04.10(-3) M = 10 micrograms/ml) to 1% human serum albumin (HSA) increased significantly from 40.2% (= control) to 47.3% in the presence of 1.18.10(-3) M = 2.84 vol% halothane. A 4-fold higher halothane concentration (4.71.10(-3) M) had an even greater effect with an increase in the thiopental fraction bound to 55.5%. With a constant HSA concentration (1% or 5%) and thiopental concentrations in the range 0.01-1.5.10(-3) M or 0.01-0.38.10(-3) M, respectively, the halothane effect (increase in thiopental binding) was always evident, as well as in other experiments with constant thiopental concentration (0.04.10(-3) M) and variation in the HSA concentration (0.5-10%). Two classes of binding sites for thiopental were apparent at the HSA molecule. In the control experiments the following binding parameters were found: n1 = 0.01, k1 = 181.10(3) M-1; n2 = 45.73, k2 = 0.08.10(3) M-1, K = 5.47.10(3) M-1. In the presence of halothane the binding parameters changed as follows: n1 = 0.14, k1 = 29.4.10(3) M-1; n2 = 11.68, k2 = 0.42.10(3) M-1, K = 9.02.10(3) M-1.

[Stereoselective differences of central nervous system-depressive action of a homologous series of 3-alkyl-thalidomide analysis]. / Stereoselektive Unterschiede der zentralnervös-depressorischen Wirkung in einer homologen Reihe von 3-Alkyl-Thalidomid-Analoga.

The racemates and the enantiomers of the 3-alkyl-thalidomide analogues 2a-c were synthesized via the lactams 1a-c. The absolute configuration of 1a-c and 2a-c was elucidated, their enantiomeric purity established. From racem. 2a 1,3-dimethylthalidomide (3) was synthesized. By means of the hexobarbital sleeping time prolongating effect in rats it was shown that racem. 2a and 3 were less CNS-depressant active than thalidomide; 3 caused a more prolonged sleeping time than 2a. Both enantiomers of 2a (i.p. 200 mg/kg) exceeded in their sleeping time prolongation action racem. 2a (same dose), whereby the (S)-enantiomer was to a factor of 1.8 more effective than the (R). With both enantiomers of 2a time and dose dependency of the effect were investigated. The enantiomers of 2b + c and 1a-c had also a prolongating effect on the hexobarbital sleeping time. Independently of the alkyl group the (S)-enantiomers were always more active than the respective (R)-enantiomers. (S)-1b (200 mg/kg) caused a long lasting loss of the righting reflexes as "own effect". Stereoselective differences between the enantiomers of 2a and 2b were observed only when a dose of 200 mg/kg was applied, whereas the higher activity of the (S)-enantiomers of 2c, 1b + c was obtained already with a lower dosage range.

Stereoselective differences in the binding of N-methylated barbiturates to human serum albumin.

The binding to human serum albumin (HSA) of a homologous series of N-methylated chiral barbiturates was studied by means of equilibrium dialysis. The length of the aliphatic side chain at C-5 of the barbiturate ring was variable, and the compounds used were: (+)-(S)- and (-)-(R)-5-methyl-(A), -5-ethyl-(B), -5-propyl-(C) and -5-butyl-(D)-1-methyl-5-phenyl-barbiturate. Binding parameters (numbers of binding classes and of binding sites in each class, affinity constant, total binding constant) were obtained from the Scatchard plot of the percent binding values. For both enantiomers of A and D as well as for (-)-(R)-B 2 classes were obtained; (+)-(S)-B and both enantiomers of C had only 1 class. The total binding constant (K) indicated a more than twofold higher binding of (-)-(R)-B (2.64 x 10(3).mol-1) and C (5.75 x 10(3).mol-1) compared with the corresponding (+)-(S)-enantiomer (1.02 and 2.00 x 10(3).mol-1, respectively); in the case of D the (+)-(S)-enantiomer was preferentially bound (K = 10.14 vs. 5.40 x 10(3).mol-1 for the (-)-(R)-enantiomer). The percent binding values of (+)-(S)-A were higher than those of (-)-(R)-A; however, the K-values of the A-enantiomers were almost identical.

[Cyclic ureas. 2. Racemates and enantiomers of imidazolidin-2-ones: synthesis, configuration and sedative-hypnotic action]. / Racemate und Enantiomere von Imidazolidin-2-onen Synthese, Konfiguration und sedativ-hypnotische Wirkung.

The racemates and the enantiomers of the imidazolidin-2-ones 2a and 2b, which can be considered as cyclic ureas, are obtained from the racemates and the enantiomers of the hydantoins 1a and 1b by reduction with LiAlH4/AlCl3. The enantiomers that are dextrorotating in ethanol possess S-configuration. In a study with Wistar-rats, 2a and 2b show sedative-hypnotic activity. The enantiomers exhibit marked enantioselective differences in their potency.

[Cyclic ureas. 1. Racemates and enantiomers of hexahydropyrimidine-2-ones: synthesis, configuration and sedative-hypnotic action]. / Zyklische Harnstoffe, 1. Mitt.: Racemate und Enantiomere von Hexahydropyrimidin-2-onen: Synthese, Konfiguration und sedativ-hypnotische Wirkung.

The racemates and the enantiomers of the hexahydropyrimidin-2-ones 2a-2e which can be regarded as cyclic ureas are obtained from the racemates and the enantiomers of the barbiturates 1a-1e by reduction with LiAlH4/AlCl3. The enantiomers of 2a-2d, dextrorotatory in ethanol, possess S-configuration. In a study with rats all cyclic ureas synthesized showed sedative-hypnotic activity. Some of the enantiomers exhibited marked enantioselecive differences in their potency.