Pharmacokinetics of digoxin and its 4‴-acetyl-and methylderivates in the rat

Summary The kinetics of absorption, of changes in blood concentration, and of biliary excretion after the i.v. and i.d. administration of 40 Ci each, of digoxin, 4-acetyldigoxin and 4-methyldigoxin were studied in biliary fistula rats. The highest blood concentrations were found after the i.v. administration of 4-methyldigoxin, which decline with a half life time of 10 h, compared with 5.6 and 4.5 h for 4-acetyldigoxin and digoxin respectively. 71%, 55% and 17% of the dose were excreted in the bile within 12 h after the i.v. administration of digoxin, 4-acetyldigoxin and 4-methyldigoxin. The blood concentrations observed after the i.d. administration of digoxin and 4-acetyldigoxin show almost identical pharmacokinetics with respect to height and elimination velocity (half life 7.0 h for digoxin and 7.5 h for 4-acetyldigoxin). In contrast, following the i.d.administration of 4-methyldigoxin, blood concentrations, which were twice as high, were observed and declined with the same half life as after the i.v. administration.Determination of the disappearance rates of these glycosides from the intestinal lumen reveals a biphasic course of absorption. A first phase, with k values of 0.4, 0.5, 1.2 for digoxin, 4-acetyldigoxin and 4-methyldigoxin respectively is followed by a second phase with k values of 0.04, 0.04, 0.001 for digoxin, 4-acetyldigoxin and 4-methyldigoxin. Thus, 4-methyldigoxin is almost completely absorbed within the first two hours, while digoxin and 4-acetyldigoxin continue to be absorbed during the following hours. The absorption velocity of digoxin from the ileum was found to be one half of that seen in the duodenum. But this slow absorption, as well, follows a biphasic course.The data indicate that 4-methyldigoxin is absorbed at a distinctly higher rate than 4-acetyldigoxin and digoxin. Acetylation in 4 position evidently provides no important advantage with respect to absorption. While this study allows the determination of absorption and excretion velocities, no account of absorption quotes is given.     

Effect of di-n-propylacetate on the ‘binding’ of GABA to a synaptosome-enriched fraction of rat cerebral cortex

The effect of di-n-propylacetate (DPA) on the binding of -aminobutyric acid (GABA) to a synaptosome-enriched fraction of rat cerebral cortex has been examined using differential centrifugation and double-isotope liquid scintillation spectrometry. DPA at 10^-4 M caused a slight decrease in GABA binding. This effect could explain in part the in vivo anticonvulsant and behavioral effects of this drug when administered to animals in high systemic doses.     

β-methyl-digoxin

Summary The tissue/plasma ratio of -methyl-digoxin for cardiac muscle in cats was about the same 24 h after a single dose of 30 g/kg as after a loading dose of 30 g/kg followed by 3 maintenance doses of 7.5 g/kg at 24 h intervals. The ratio for the brain increased 2-fold during that time.After the i.v. injection of a toxic loading dose of 70 g/kg -methyl-digoxin or digoxin, maintenance doses of as little as 15 g/kg at 48 h intervals sufficed to maintain the minimum plasma glycoside concentrations determined by RIA at about 3 ng/ml. There was no difference in the plasma concentrations or in the severity of intoxication produced by both glycosides.Cats vomited within 3 h after i.v. injection of 100 g/kg -methyl-digoxin, whereas a loading dose of 30 g/kg followed by 3 injections of 7.5 g/kg at 24 h intervals were well tolerated. The concentration of radioactivity in the brain 3 h after 100 g/kg was less than 24 h after the last injection of 7.5 g/kg in the experiments with repeated dosage.Cerebral side-effects such as vomiting, loss of appetite and weight were better correlated with the glycoside concentrations in the plasma than with those in the brain.     

Serum glycoside concentrations after single or repeated intravenous doses ofβ-methyl-digoxin and digoxin

Summary The aim of the present investigation was to estimate the ratio of the intravenous doses of-methyl-digoxin and digoxin required to produce identical serum glycoside concentrations in man.20 patients on intravenous maintenance therapy were changed from-methyl-digoxin to the identical dose of digoxin or vice versa. Each drug was given for 7 days. Serum concentrations 13% higher were found during administration of-methyl-digoxin. Assuming a half life of 60 h after with drawal, the dose of digoxin producing the same minimum serum concentration was estimated to be 1.16 times higher than that of-methyl-digoxin.18 healthy volunteers received 0.4 mg -methyldigoxin, and 23 the same dose of digoxin, as an intravenous infusion over 2 h. The serum concentrations and urinary glycoside excretion were measured over a period of 32 hrs. During the first hour after the infusion the serum concentration of digoxin declined more rapidly than that of-methyl-digoxin. Thereafter, the ratio of the serum concentrations did not change appreciably up to the end of the investigation. The area under the serum concentration/time curve was about 13% greater for-methyl-digoxin than for digoxin; this difference was not significant.The average renal clearance was 96±9 ml for-methyl-digoxin, 151±13 ml for digoxin. Since the total body clearance of digoxin is only about 1.16 times higher than that of-methyl-digoxin, the lower renal clearance of-methyl-digoxin must partly be compensated by higher extrarenal clearance.From the ratios of the areas under the serum concentration/time curves after single doses of -methyldigoxin and digoxin, and the minimum serum concentrations during maintenance therapy, it was concluded that the dose of digoxin to produce the same average serum concentrations would be about 1.15 times higher than that of-methyl-digoxin. In comparison with the large variations in individual dosage of digoxin and-methyl-digoxin, this difference is too small to be of practical importance.     

Differential modulation by muscimol and baclofen on antinociception induced by morphine, β-endorphin,d-Pen2,5-enkephalin and U50,488H administered intracerebroventricularly in the mouse

The present study was designed to investigate the modulatory effects of stimulation of GABA_A and GABA_B receptors at supraspinal sites on antinociception induced by supraspinally administered -, -, -, and -opioid receptor agonists. The effects of the GABA_A and GABA_B receptor agonists, muscimol and baclofen respectively, on the antinociception induced by morphine (a -receptor agonist), -endorphin (an -receptor agonist), D-Pen^2,5-enkephalin (DPDPE, a -receptor agonist) and U50,488H ({trans-3,4-di-chloroN-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeocetamide}; a -receptor agonist) injected intracerebroventricularly (i.c.v.) were studied. The anti-nociception was assayed using the tail-flick and hot-plate tests. Muscimol at doses of 25–200 ng, administered i.c.v. alone did not affect the latencies of tail-flick and hot-plate thresholds, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by i.c.v. administered morphine (2 g), -endorphin (1 g), DPDPE (10 g), and U50,488H (60 g). Baclofen (1.25–10 ng) administered i.c.v. alone did not affect the latencies of the tail-flick and hot-plate responses, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by -endorphin and U50,488H, without affecting morphine-or DPDPE-induced responses. Our results indicate that activation of GABA_A receptors at the supraspinal sites by i.c.v. injection of muscimol antagonizes antinociception induced by supraspinally administered -, -, -, and -opioid receptor agonists. On the other hand, activation of GABA_B receptors at supraspinal sites by i.c.v. baclofen antagonizes antinociception induced by i.c.v. administered - and -opioid agonists, but not - or -opioid agonists.     

Modeling of drug response in individual subjects

Pharmacokinetic and drug response data from individual subjects are analyzed empirically by two different mathematical techniques. The drugs involved are the antiarrhythmic agent disopyramide, whose kinetics can be described by a two-compartment model, and two cardiac glycosides, digoxin and -methyl digoxin, for which three-compartment models are appropriate. The first analytical approach uses multiple linear regression to describe response in terms of the amount of drug in several kinetic compartments. The second approach describes response in terms of the drug concentration in an effect compartment. Both approaches describe the data equally well and require the same number of parameters for model specification.     

Effect of prednisolone and ketotifen onβ 2-adrenoceptors in asthmatic patients receivingβ 2-bronchodilators

Summary In 13 patients with bronchial asthma, who were on ₂-adrenergic bronchodilator therapy, the effects of prednisolone and ketotifen on lymphocyte ₂-adrenoceptor density and -responsiveness were investigated. The mean lymphocyte ₂-adrenoceptor density and -responsiveness was significantly lower than in healthy controls, presumably due to the long-term ₂-adrenergic bronchodilator treatment. Both prednisolone 100 mg i.v. and ketotifen 1 mg b.d.p.o. for 6 days rapidly improved lymphocyte ₂-adrenoceptor function. 16 h after prednisolone and about 6 days after the first dose of ketotifen lymphocyte ₂-adrenoceptor density and-responsiveness had risen to values within the range in normal volunteers.The improvement of lymphocyte ₂-adrenoceptor function was accompanied by a significant increase in peak expiratory flow rate before and after inhalation of salbutamol.It is concluded that prednisolone and ketotifen may act beneficially on the recovery of ₂-adrenoceptor responsiveness to ₂-adrenergic bronchodilators in tolerant asthmatic patients.     

Stimulation of central serotonin turnover by β-adrenoceptor agonists

Summary The ₂-stimulators salbutamol (0.3–30 mg/kg i.v.) and clenbuterol (0.3 and 1 mg/kg i.v.), and, to a lesser extent, the ₁-stimulators dobutamine (30 mg/kg i.v.) and prenalterol (30 mg/kg i.v.) increased serotonin metabolism in several rat brain areas, as indicated by increased concentrations of 5-hydroxyindoleacetic acid (5-HIAA) or increased tryptophan hydroxylation in vivo. With salbutamol, increases in 5-HIAA in c. striatum and brainstem, but not in cortex, were observed after intraventricular administration of relatively low doses (3–30 g). Direct application of the compound into the dorsal raphe nucleus at doses of 100 ng and 1 g were without effect, and only mininal 5-HIAA increases occurred after the high dose of 10 g. The effects of salbutamol on the concentrations of 5-HIAA were antagonized by both propranolol and WB4101, indicating an involvement not only of -receptors but also of postsynaptic -receptors.The evidence for and against a central site of action of -agonists with respect to their effect on serotonergic systems is discussed.     

β-Methyl-digoxin

Summary In guinea pigs under urethane anaesthesia the concentrations of radioactivity in the plasma, the liver and the heart and the protein binding of radioactivity were measured 1 h after the intravenous injection of 0.2 moles/kg -methyldigoxin or digoxin. The distribution coefficients were calculated between the concentrations in the plasma water and the tissues. Apart from a slightly higher distribution coefficient for -methyl-digoxin than for digoxin between liver and plasma water there was no significant difference between the two glycosides.In guinea pigs under barbital anaesthesia, cardiac failure was produced by additional doses of barbital-Na. Bemegride was given to counteract the effects of barbital on the vasomotor centre. -Methyl-digoxin and digoxin were infused until cardiac arrest. For each animal the doses were calculated which led to an increase in cardiac performance by 50 g · cm/sec, arrhythmia, ventricular fibrillation or cardiac arrest. The therapeutic range was calculated from the doses producing arrhythmias and those increasing cardiac performance by 50 g · cm/sec (therapeutic dose).There was no difference between the therapeutic and toxic doses and the therapeutic ratios of -methyl-digoxin and digoxin.     

Protein binding of digoxin in human serum

Summary The protein binding of digoxin in human serum was investigated using equilibrium dialysis and tritium-labelled digoxin. A constant protein bound fraction of about 30% was found over a wide range of concentrations of digoxin including therapeutic levels. Interpretation of the findings according to the law of mass-action showed an association constantK = 0.68·10^–5l/mol; and, the number of binding sites,n , indicating an almost infinite apparent maximum binding capacity and a very small affinity of human serum proteins for digoxin.Supported by the Schweizer Nationalfond zur Förderung der wissenschaftlichen Forschung.     

Rectal Absorption Enhancement of Des-Enkephalin-γ-Endorphin (DEγE) by Medium-Chain Glycerides and EDTA in Conscious Rats

The stability of the neuroleptic peptide des-enkephalin--endorphin (DEE; Org 5878) in the rectal lumen and the rectal bioavailability of DEE were investigated in conscious rats. Furthermore, the influence of peptidase inhibition, peptidase saturation, and absorption enhancement on DEE bio-availability were evaluated. Na₂EDTA (0.25%, w/v) prolonged the degradation half-life of DEE in the ligated colon from 33 ± 7 to 93 ± 45 min. Without adjuvant, tritium-labeled DEE was absorbed from the rat rectum to a very low extent (0–4%). After administration of an excess of unlabeled DEE or with Na₂EDTA, comparable results were obtained. The medium-chain glyceride preparation MGK markedly enhanced the rectal DEE bioavailability, up to 8–20%, which was further increased to 10–44% by coadministration of Na₂EDTA. No substantial influence of varying the rectal delivery rate was observed. The results suggest that absorption enhancement and enzyme inhibition both are essential for effective increase of rectal peptide bioavailability.     

Presynaptic dopamine DA2-receptors in rabbit jejunal arteries

Summary Excitatory junction potentials (e.j.ps) evoked by nerve stimulation with 15 pulses at 1 Hz were recorded from muscle cells of rabbit isolated jejunal arteries. LY 171555 1 mol/l, SKF 38393 10 mol/l, dopamine 10 ol/l and clonidine 0.1 mol/l depressed all e j.ps in the train. The percentage inhibition was inversely related to the number of pulses. S- and R-sulpiride, 10 mol/l, domperidone 1 mol/l, SCH 23390 1 mol/l and rauwolscine 1 mol/l did not change, or even depressed the first e j.ps. Of these compounds only S- and R-sulpiride, 10 mol/l and rauwolscine 1 mol/l facilitated the late e.j.ps. The percentage facilitation increased with the number of pulses until a maximum was reached; rauwolscine 1 ol/l had the largest effect. S- and R-sulpiride, 10 mol/l, as well as domperidone 1 ol/l antagonized the action of LY 171555 1 mol/l. S-Sulpiride was more potent than its R-isomer. SCH 23390 1 mol/l and rauwolscine 1 mol/l blunted the effect of SKF 38393 10 mol/l. Rauwolscine 1 mol/l slightly reduced the inhibition by dopamine 10 mol/l; S-sulpiride 10 mol/l was antagonistic only in the presence of rauwolscine 1 mol/l. When rauwolscine 1 mol/l, prazosin 0.1 mol/l, propranolol 1 mol/l and cocaine 10 mol/l was added to the medium, dopamine 10 mol/l continued to produce the same depression of e j.ps, as in the absence of these compounds. Under such conditions S-sulpiride 10 mol/l also counteracted dopamine 10 gmol/l. Rauwolscine 1 mol/l prevented the effect of clonidine 0.1 mol/l. The antagonists were not absolutely selective against only one type of agonist. We suggest that both presynaptic DA₂- and postsynaptic DA₁-receptors are present in rabbit jejunal arteries. The activation of either receptor-type may depress the e j.ps. Dopamine interferes with neuroeffector transmission due to ₂-adrenoceptor agonist properties; its DA₂-effect is unmasked only after ₂-adrenoceptor blockade. There was no evidence for a co-transmitter function of dopamine. Send offprint requests to P. Illes at the above address     

Distinct down-regulation of cardiac β1- and β2-adrenoceptors in different human heart diseases

Summary Cardiac -adrenoceptor density and ₁- and ₂-subtype distribution were examined in human left ventricular myocardium from transplant donors serving as controls and from patients with mitral valve stenosis, aortic valve stenosis, idiopathic dilated cardiomyopathy, and ischaemic cardiomyopathy respectively. The total -adrenoceptor density was similar in transplant donors and patients with moderate heart failure (NYHA II–III) due to mitral valve stenosis, but was markedly reduced in all forms of severe heart failure (NYHA III–IV) studied. A reduction of both ₁- and ₂-adrenoceptors was found in patients with severe heart failure due to mitral valve stenosis or ischaemic cardiomyopathy. In contrast, a selective down-regulation of ₁-adrenoceptors with unchanged ₂-adrenoceptors and hence a relative increase in the latter was observed in idiopathic dilated cardiomyopathy and aortic valve stenosis. It is concluded that the extent of total -adrenoceptor down-regulation is related to the degree of heart failure. Selective loss of ₁-adrenoceptors is not specific for idiopathic dilated cardiomyopathy but also occurs in aortic valve stenosis. Changes in ₁- and ₂-subtype distribution are rather related to the aetiology than to the clinical degree of heart failure. Send offprint requests to M. Steinfath at the above address     

Evaluation of P2-purinoceptor antagonists at two relaxation-mediating P2-purinoceptors in guinea-pig taenia coli

The guinea-pig taenia coli possesses two relaxation-mediating receptors for nucleotides: a prototypic P_2Y-purinoceptor, which is activated by adenosine 5-O-(2-thiodiphosphate) (ADPßS), and a separate receptor for ,-methylene ATP (,-MeATP). Effects of several as yet incompletely characterized P₂-purinoceptor antagonists at these receptors were examined.The concentration-relaxation curve of ADPßS was shifted to the right by reactive blue 2, suramin, 8-(3,5-dinitro-phenylenecarbonylimino)-1,3,5-naphthalenetrisulphonic acid (XAMR0721; at 1000 M only), pyridoxalphosphate-6-azophenyl-2,5-disulphonic acid (iso-PPADS), pyridoxal 5-phosphate, trypan blue and Evans blue (at 320 M only). Schild plots for the antagonism of reactive blue 2, suramin, iso-PPADS and pyridoxal 5-phosphate against ADPßS had slopes <1. The concentration-relaxation curve of ,-MeATP was shifted to the right by reactive blue 2, suramin, XAMR0721, iso-PPADS, pyridoxal 5-phosphate and trypan blue but not by Evans blue (320 M). Schild plots for the antagonism of suramin, XAMR0721 and iso-PPADS against ,-MeATP had slopes >1. Only XAMR0721 differed clearly in potency against the two nucleotides: it was considerably more potent against ,-MeATP than against ADPßS. 2-Methylthio ATP (MeSATP; 1 M) and ATP (100 M) were degraded by pieces of taenia coli. All antagonists except trypan blue attenuated the degradation of either or one of the two nucleotides.The selective effect of XAMR0721 against ,-MeATP confirms the existence of two relaxation-mediating P₂-purinoceptors in guinea-pig taenia coli. Comparison of the apparent affinities of the antagonists for the two taenia coli receptors with affinities for the P_2X-purinoceptor of the rat vas deferens shows that reactive blue 2, suramin, iso-PPADS, pyridoxal 5-phosphate and trypan blue have little selectivity for any of the three receptors. XAMR0721, which has been shown to possess relatively high affinity for the P_2Y-purinoceptor in turkey erythrocytes, was very weak at the P_2Y-receptor of the taenia, thus supporting the existence of pharmacologic P_2Y-receptor subtypes. Evans blue, with little effect in the taenia coli but a marked effect in the rat vas deferens, is the most selective P_2X-(versus P_2Y-) purinoceptor antagonist presently known, although its effect on the degradation of nucleotides must be kept in mind.     

Über das bradykininbildende Prinzip des Schlangengiftes

Summary 1. The bradykinin releasing principle of the venom of Bothrops jararaca and of Crotalus atrox is partly dialysable through cellophane. With Crotalus venom about 10% of the total activity are found in the dialysate.2. The dialysates are free of the proteolytic and coagulating (Bothrops) as well as of the tryptic principle of the venoms as measured by the hydrolysis of benzoyl-argininamid. Beside the bradykinin releasing principle they contain an esteratic activity, which splits the methylester of benzoylarginin.3. It is concluded from the results that the bradykinin releasing principle may be identical with the esteratic principle but not with the proteolytic and tryptic nor with the fibrinogen coagulating principle. On the other hand it may belong to the group of Kontaktstoffe which like agar, inulin, starch and the dextranes, release anaphylatoxin when they get into contact with serumproteins.4. Rabbits are about 8 times more sensitive than cats against the bloodpressure lowering action of bradykinin.5. The question is discussed whether the snake venoms contain only one bradykinin releasing factor which is dialysable and of low molecular weight, or whether there are different factors, some of which have a high molecular weight and are therefore not dialysable.

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Mit 7 Textabbildungen

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Herrn Professor Dr. Paul Wels zum 70. Geburtstag gewidmet.

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Die Arbeit wurde mit finanzieller Unterstützung der U.S. Department of the Army, European Research Office, durchgeführt.Eine kurze Mitteilung erfolgte in den Naturwissenschaften (Contzen, Holtz u. Raudonat 1959).     

β2-Adrenergic Receptor Genotype-Related Changes in cAMP Levels in Peripheral Blood Mononuclear Cells After Multiple-Dose Oral Procaterol

Purpose. To evaluate the ₂-adrenergic receptor (₂AR) genotype frequency in the Japanese population and the relationship between ₂AR genotype at amino acid position 16 (₂AR-16) and desensitization to ₂-agonist ex vivo. Methods. The ₂AR genotypes at amino acid positions 16, 27, and 164 of 92 healthy Japanese subjects were determined by polymerase chain reaction-restriction fragment-length polymorphism. The relationship between the ₂AR-16 genotype and the desensitization to ₂-agonist was examined in 10 male subjects ex vivo. Procaterol tablet (HCl salt, 50g, Meptin®) was given orally for 5 days, and peripheral blood was obtained before and after 5 days of consecutive medications followed by the assessment of the intracellular cAMP levels in peripheral blood mononuclear cells after incubation with or without procaterol hydrochloride (0-1000 ng/mL). Results. Allele frequency was Arg16:Gly16 = 46%:54%, Gln27:Glu27 = 92%:8%, and Thr164:Ile164 = 100%:0%, respectively. The cAMP levels were increased by incubation with procaterol hydrochloride, and the increase was suppressed after 5 days of consecutive medications. The suppression was more significant in the homozygote for Gly16 than the homozygote for Arg16. Conclusions. The desensitization to ₂-agonist was associated more frequently with the mutation at ₂AR-16 (Gly16).     

Enhancement of the Antiinflammatory Effect of Ethyl 4-Biphenylyl Acetate in Ointment by β-Cyclodextrin Derivatives: Increased Absorption and Localized Activation of the Prodrug in Rats

Ethyl 4-biphenylyl acetate (EBA) is a prodrug of the antiinflammatory 4-biphenylyl acetic acid (BPAA). The inclusion complexes of EBA with -cyclodextrin (-CyD), heptakis(2,6-di-O-methyl)--cyclodextrin (DM--CyD), and 2-hydroxypropyl--cyclodextrin (HP--CyD) at a molar ratio of 1:2 (EBA:cyclodextrin) were prepared and used to make hydrophilic antiinflammatory ointments. The in vitro release of EBA from the ointments was enhanced by complexation in the order of -CyD < DM--CyD HP--CyD. The improvement correlated with the improved solubility and not with the decreased diffusibility observed to occur upon the complexation of EBA. In vivo the complexation with cyclodextrin derivatives increased both the release of EBA from the vehicle and its conversion in the underlying tissue to BPAA, but the total of EBA and BPAA in the tissue was decreased. In vitro studies confirmed that the effects of cyclodextrin derivatives on the conversion were exerted indirectly. The combination of the enhanced release and of the enhanced prodrug hydrolysis by esterases in the site where the antiinflammatory action is required resulted in increased therapeutic effects. In the model of carrageenan-induced acute edema in rat paw, the complexation improved the therapeutic effects over those of EBA alone in the order of -CyD < DM--CyD < HP--CyD. HP--CyD may be a particularly useful cyclodextrin derivative since it improves the topical availability and does not irritate tissues.     

Über die Wirkung einiger herzwirksamer Bisguanylhydrazone auf den Veratrineffekt am Frosch-Sartoriusmuskel

Zusammenfassung Die Wirkung einiger Guanylhydrazone sowie von Tyramin auf die Veratrine-Response des Froschsartoriusmuskels wurden untersucht. Von den drei herzglykosidartigen Bisguanylhydrazonen zeigten BG 60 und BG 31 den unspezifischen Veratrinantagonismus des Chinidins. BG 85 hingegen beeinflußte die VR herzglykosidartig. Von den drei tyraminartigen Substanzen BG 81, MG 41 und Tyramin wirkten die letzten zwei chinidinartig, während BG 81 trotz seiner tyraminartigen Wirkung die VR herzglykosidartig beeinflußte.

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Summary A series of guanylhydrazones was synthesized, some of the substances had a cardiac glycoside-like activity on the mammalian heart whereas other ones acted tyramine-like. The effect of some guanylhydrazones of each kind of action on the veratrine response (VR) of the frog's sartorius muscle should be investigated. Following substances were synthesized: 1. with cardiac glycoside-like activity 3,3-dimethyl-4,4-diacetyldiphenylbisguanylhydrazone (BG 60), progesteronebisguanylhydrazone (BG 31), p-aceto-m-methyl-phenyl-acetonyl-ether-bisguanylhydrazone (BG 85) 2. with sympathomimetic activity: p-aceto-phenyl-acetonyl-ether-bisguanylhydrazone (BG 81) and p-hydroxybenzaldehyd-monoguanylhydrazone (MG 41). The characteristic influence of the cardiac glycosides on the VR was only to be seen with BG 85 and BG 81. BG 60, BG 31 and BG 41 showed a quinidine-like effect on the VR. That means that from 3 guanylhydrazones with cardiac glycoside-like activity on the mammalian heart two of them had a quinidine-like effect on the VR and only one of them showed the typical cardiac glycoside-like effect on the VR. On the other hand among the guanylhydrazones with tyramine-like activity on the mammalian heart there is one, BG 81, which influenced the VR like a cardiac glycoside.

     

The influence of taurocholate and dehydrocholate choleresis on plasma disappearance and biliary excretion of indocyanine green in the rat

Summary The pharmacokinetics of indocyanine green (ICG; 3.9 moles/kg and 12.9 moles/kg) were investigated in rats given infusion of either saline, taurocholate (106 moles/h) or dehydrocholate (106 or 268 moles/h). During the infusion of saline and taurocholate the plasma concentration of ICG decreased in a mono-exponential manner. However, with dehydrocholate the clearance of ICG from plasma showed two phases with different half lives. The half life of the rapid component (2.2 min) was about the same as the one found in the control experiments.After injection of 12.9 moles/kg ICG the biliary excretion of the dye increased by 138% during taurocholate administration, while an equimolar dehydrocholate infusion resulted in a mean increament of 55%. Under these circumstances the bile flow was stimulated by 195% and 297% resp.With the lower dose of ICG (3.9 moles/kg) however, there was no stimulation of the biliary ICG excretion with taurocholate. At this dose level an infusion of dehydrocholate (106 mol/h) enchanced the biliary output of ICG by approximately 54%, while administration of 268 mol/h resulted in a slight but significant decrease of 31%.These observations can be explained by assuming interaction of the bile acids with the hepatic transport of ICG at different sites. The appearance of the second component of the plasma curve during dehydrocholate infusion is possibly related to a diminished hepatic storage capacity for ICG and is not due to an effect on the primary hepatic uptake or biliary output of the dye.     

Plasma levels and β-blocking effect of α-hydroxymetoprolol—Metabolite of metoprolol—in the dog

The plasma levels and the - blocking effect of metoprolol and its active metabolite - hydroxymetoprolol have been studied after i.v. bolus injections of the substances to dogs. For both substances the - blockade increased with the dose, and there was a linear relationship between percent reduction in exercise heart rate and the logarithm of plasma concentration. The dose of the metabolite, however, had to be 5 times higher than that of metoprolol to induce the same degree of - blockade. Because of differences in the volume of distribution, 2.0 liters/kg for - OH-metoprolol and 3.5 liters/kg for metoprolol, the 5 times higher dose of - OH-metoprolol resulted in 10 times higher plasma levels of the metabolite than of metoprolol. - OH-Metoprolol was more slowly eliminated (t_1/27.0 hr, total body clearance 3.5 ml-kg^–1-min^–1) than metoprolol (t_1/22.0 hr, total body clearance 20.0 ml-kg^–1-min^–1). Approximately 5% of an i.v. dose of metoprolol was metabolized to - OH-metoprolol. The half-life of the endogenously formed metabolite was the same as after an i.v. dose of the compound.