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  • 1
    Electronic Resource
    Electronic Resource
    Inhibition by K+ of uptake2 of3H-(±)-isoprenaline in the perfused rat heart (1986)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 334 (1986), S. 393-396 
    Details
    ISSN: 1432-1912
    Keywords: Isoprenaline ; Uptake2 ; Extracellular potassium ; Rat heart
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The kinetics of the inhibitory effect of extracellular K+ on uptake2 of3H-(±)-isoprenaline were determined in isolated hearts obtained from reserpine-pretreated rats; catechol-O-methyl transferase was inhibited. 1. Initial rates of uptake2 of a very low concentration of3H-(±)-isoprenaline (10 nmol/l) were determined in the presence of various extracellular concentrations of K+ (2.7 to 60 mmol/l). The inhibitory effect of K+ was concentration-dependent with an IC50 of about 20 mmol/l. — In these experiments KCl was added to the perfusion solution, and some hypertonicity resulted. In some experiments NaCl was added to a solution containing 5 mmol/l K+ to result in the same degree of hypertonicity as that obtained for 60 mmol/l K+; hypertonicity increased the initial rate of uptake2 of3H-(±)-isoprenaline. Thus, the inhibitory effect of K+ had been slightly underestimated. 2. In subsequent experiments the increase of the concentration of K+ in the perfusion fluid to 30 mmol/l was compensated for by a corresponding reduction of Na+. Initial rates of uptake2 of 10 nmol/l3H-(±)-isoprenaline were determined in the absence and presence of various concentrations of unlabelled (±)-isoprenaline. At 30 mmol/l K+ the IC50 (=K m for uptake2) did not significantly differ from that determined in an earlier study of 2.7 mmol/l K+ (Grohmann and Trendelenburg 1984). Finally, theV max for uptake2 of3H-(±)-isoprenaline was determined at either 2.7 or 30 mmol/l K+. At 30 mmol/l K+ theV max was only about 1/4 of that observed at 2.7 mmol/l K+. 3. Extracellular K+ inhibits uptake2 of3H-(±)-isoprenaline primarily by a reduction ofV max.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00569376
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  • 2
    Electronic Resource
    Electronic Resource
    The effect of partial inhibition of monoamine oxidase on the steady-state rate of deamination of 3H-catecholamines in two metabolizing systems (1986)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 333 (1986), S. 253-261 
    Details
    ISSN: 1432-1912
    Keywords: Neuronal deamination ; Extraneuronal deamination ; Rat vas deferens ; Rat heart ; Monoamine oxidase ; Pargyline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Two different “deaminating systems” were compared (i.e., intact tissues in which an uptake process translocates the 3H-catecholamine from the extracellular space to the intracellular MAO): 1) the adrenergic nerve endings of the rat vas deferens exposed to 10 nmol/l 3H-(−)-noradrenaline, and 2) the extraneuronal deaminating system of the rat heart perfused with 50 nmol/l 3H-(−)-adrenaline. Vesicular uptake and COMT were inhibited. In both systems MAO was partially inhibited by pargyline, and the steady-state tissue content of the 3H-catecholamine was determined as well as the steady-state rate of deamination. 1. Rat vas deferens (preincubated with 10–40 nmol/l pargyline for 30 min). Inhibition of neuronal MAO caused not more than a moderate decrease of the steady-state rate of deamination of 3H-(−)-noradrenaline, but the steady-state tissue content was greatly increased. Determinations of the activity of MAO in homogenates of vasa deferentia showed that preincubation with 10 and 20 nmol/l pargyline inhibited the enzyme by 80 to 95%. 2. Rat heart (of animals pretreated with 1 to 30 mg/kg pargyline). Inhibition of extraneuronal MAO caused a steep decline of the steady-state rate of deamination of 3H-(−)-noradrenaline but only a small rise in the steady-state tissue content. 3. The decisive difference between the two deaminating systems lies in the fact that the ratio “k mao/k out” (where the two k-values characterize the activity of the unsaturated intracellular MAO and the ability of the 3H-catecholamine to leave the relevant cells, respectively) is much higher for the neuronal deaminating system exposed to 3H-(−)-noradrenaline than for the extraneuronal deaminating system exposed to 3H-(−)-adrenaline. Whenever this ratio is high, pronounced (but incomplete) inhibition of MAO results in a very pronounced increase in the intracellular steady-state 3H-amine concentration (during exposure of the tissue to a 3H-catecholamine); as far as the steady-state rate of deamination is concerned, the pronounced rise in substrate concentration largely masks the pronounced degree of inhibition of MAO. When, however, the ratio is close to unity, inhibition of MAO fails to result in any pronounced increase in the intracellular steady-state 3H-amine concentration; as a consequence, any pronoumced inhibition of MAO is then reflected by a pronounced decrease of the steady-state rate of deamination. 4. From the present results it is concluded that, in experiments with intact tissues, the degree of inhibition of MAO cannot be derived from measurements of rates of deamination of 3H-catecholamines.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00512938
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature sensitivity of the extraneuronal uptake and metabolism of isoprenaline in the perfused rat heart (1979)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 306 (1979), S. 229-239 
    Details
    ISSN: 1432-1912
    Keywords: Extraneuronal uptake ; Temperature ; Rat heart ; Catecholamines ; Rate constants for efflux ; Extraneuronal COMT
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The influence of lowering the temperature (from 37° to either 27° or 20°C) on extraneuronal mechanisms was studied in the rat heart perfused with 3H-isoprenaline. 1. During perfusion at a constant rate, lowering of the temperature increased the resistance to flow. The consequent impairment of the effectiveness of the perfusion of the tissue accounts for most (or all) of the temperature-sensitivity of the non-saturable (probably diffusional) extraneuronal uptake of isoprenaline. 2. For various other extraneuronal mechanisms the effect of lowering the temperature clearly exceeded that attributable to changes in perfusion. This applied to the V max (but not to the K max) of saturable extraneuronal uptake and extraneuronal O-methylation, as well as to the rate constants for the efflux of isoprenaline and its O-methylated metabolite, OMI. 3. Lowering of the temperature impaired the efflux of isoprenaline from compartment III (characterized by Bönisch et al., 1974, as having a half time of about 10 min) much more than that from compartment IV (characterized by Bönisch et al., 1974, as having a half time of about 25 min). Since these effects are similar to those of an inhibitor of extraneuronal uptake, corticosterone, it is possible that amine efflux from compartment III (but not from compartment IV) is carrier-mediated. 4. It is concluded that the temperature-sensitivity of the extraneuronal accumulation of catecholamines reported in the literature is not solely due to extraneuronal uptake being temperature-sensitive; the intracellular enzyme and the rate constants for the efflux of amine and metabolite are also greatly influenced by temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00507108
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of monoamine oxidase and catechol-O-methyl transferase on the distribution of 3H-(±)-noradrenaline in rabbit aortic strips (1978)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 302 (1978), S. 181-194 
    Details
    ISSN: 1432-1912
    Keywords: Rabbit aorta ; MAO ; COMT ; Efflux of noradrenaline ; Metabolism of noradrenaline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Rabbit aortic strips were incubated with 1.18 μM 3H-(±)-noradrenaline for 30 min, and the accumulation of noradrenaline in the strips was measured as well as the total formation of metabolites. Some strips were exposed to 30 μM cocaine or 87μM corticosterone to inhibit neuronal and extraneuronal uptake, respectively. In some strips monoamine oxidase (MAO) and/or catechol-O-methyl transferase (COMT) was inhibited by pargyline and/or U-0521. Of the extraneuronal enzymes COMT is much more important than MAO; there is virtually no accumulation of noradrenaline in extraneuronal tissue when either COMT or both enzymes are intact. For adrenergic nerve endings, MAO is most important; very little or no COMT activity is associated with the nerve ending. When MAO is intact, there is virtually no axoplasmic accumulation of noradrenaline. Storage vesicles and MAO compete for axoplasmic noradrenaline. Neuronal and extraneuronal uptake and metabolism do not seem to compete for noradrenaline. 2. Other strips were incubated as described above and then washed out with amine-free solution for 240 min. When storage vesicles are intact, the long half time of the late neuronal efflux of radioactivity reflects the long half time for the conversion of “bound” to “free” amine; most of the free amine is then deaminated to dihydroxyphenyl glycol (DOPEG) when MAO is intact. Axoplasmically accumulated noradrenaline generates an efflux with a half time that is shorter than that for vesicular noradrenaline. A small proportion of the neuronal efflux of noradrenaline is taken up extraneuronally and converted to normetanephrine (NMN). When little or no noradrenaline accumulates in the strips during initial incubation, the strips lose some metabolites (DOPEG, NMN) quickly during wash out, while the acid metabolite, dihydroxymandelic acid (DOMA), leaves the tissue with a long half time; late efflux can then consist nearly exclusively of DOMA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00517985
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  • 5
    Electronic Resource
    Electronic Resource
    The neuronal and extraneuronal uptake and metabolism of 3H-(−)-noradrenaline in the perfused rat heart (1978)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 303 (1978), S. 21-35 
    Details
    ISSN: 1432-1912
    Keywords: (−)-Noradrenaline ; Neuronal uptake ; Extraneuronal uptake ; Extraneuronal metabolism ; COMT ; MAO ; Efflux of noradrenaline metabolites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Hearts were obtained from reserpine-pretreated rats and perfused with 0.95 μM 3H-(−)-noradrenaline. The rate of removal of 3H-noradrenaline from the perfusion fluid was measured (from the arterio-venous difference) as well as the rate at which the 3H-metabolites appeared in the venous effluent. 2. When either 30 μM cocaine or 87 μM corticosterone was added under steady-state conditions during perfusion with 3H-noradrenaline (to inhibit neuronal and extraneuronal uptake, respectively), each inhibitor reduced the removal of noradrenaline by about 50%; in the presence of both inhibitors removal was abolished. 3. Dihydroxymandelic acid (DOMA) was of neuronal, normetanephrine (NMN) of extraneuronal origin; dihydroxyphenylglycol (DOPEG) and the OMDA fraction (containing methoxyhydroxyphenylglycol-MOPEG-and methoxyhydroxymandelic acid-VMA) were formed both neuronally and extraneuronally. 4. The extraneuronal metabolism of 3H-noradrenaline was in quick equilibrium with the 3H-noradrenaline in the perfusion fluid; most of the total formation of DOPEG, MOPEG and NMN was recovered from the venous effluent. 5. Extraneuronally formed DOPEG, MOPEG and NMN distributed in the tissue with half times corresponding to their half time for efflux. 6. Inhibition of monoamine oxidase (MAO) by pargyline increased the extraneuronal formation of NMN; MAO and catechol-O-methyl transferase (COMT) appear to be contained in the same extraneuronal compartment. 7. The extraneuronal accumulation of 3H-noradrenaline required 30 min or more to reach a steady state; inhibition of one or both enzymes slowed this process. Inhibition of MAO increased the extraneuronal accumulation of 3H-noradrenaline; inhibition of COMT failed to do so, since the enzyme inhibitor (U-0521) was a weak inhibitor of extraneuronal uptake. 8. The rate constants for the efflux of the metabolites of noradrenaline decreased in the order of MOPEG〉DOPEG〉NMN〉DOMA〉VMA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00496182
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  • 6
    Electronic Resource
    Electronic Resource
    The neuronal and extraneuronal distribution of 3H(−)-noradrenaline in the perfused rat heart (1979)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 308 (1979), S. 199-210 
    Details
    ISSN: 1432-1912
    Keywords: (−)-Noradrenaline ; Extraneuronal metabolism ; COMT ; MAO ; Distribution of noradrenaline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. After inhibition of both COMT and MAO, rat hearts were perfused with 1 μM 3H-(−)-noradrenaline for 30 min. Cocaine-sensitive neuronal and corticosterone-sensitive extraneuronal compartments were of about equal importance for the distribution of the amine into the heart. The absence of calcium from the perfusion fluid increased the axoplasmic and decreased the extraneuronal distribution of noradrenaline. 2. Under the same experimental conditions, hearts were washed out after the initial perfusion, and the efflux curves were subjected to compartmental analysis. For the nerve endings three distribution compartments were identified (the axoplasmic compartments B and C, characterized by half times of 8 and 45 min, respectively, as well as the vesicular “bound fraction”), while there was only one important extraneuronal distribution compartment (compartment C with a half time of about 45 min). 3. Efflux from the axoplasmic compartment C was accelerated by unlabelled noradrenaline, not affected by cocaine, reduced by lowering of the temperature from 37° to 27° C. Moreover, it was greatly accelerated by the omission of sodium from the wash-out solution. 4. Efflux from the extraneuronal compartment C, on the other hand, was not affected by the presence of unlabelled noradrenaline, and impaired by lowering of the temperature as well as by corticosterone. The omission of sodium from the wash-out solution caused an acceleration of the extraneuronal efflux which was significantly smaller than that of axoplasmic efflux. 5. Other hearts were perfused with either 1 or 16.7 μM 3H-(−)-noradrenaline (plus 30 μM cocaine) for 30 min and then washed out with amine-free solution; in these experiments either MAO or COMT was inhibited. When MAO was inhibited, the efflux curves for normetanephrine indicated that the accumulation of the amine in the extraneuronal compartment C can easily exceed that concentration which saturates the intracellular COMT. When MAO was not inhibited, afflux curves for DOPEG failed to provide any evidence for saturation of extraneuronal MAO. These results are in good agreement with earlier determinations of the kinetic constants of the “extraneuronal metabolizing systems” of the rat heart (Fiebig and Trendelenburg, 1978b). 6. The results indicate that extraneuronal mechanisms play an important role in the rat heart, and also that the extraneuronal compartment C (for noradrenaline) corresponds to the compartment III (for isoprenaline described by Bönisch et al. (1974).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00501383
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  • 7
    Electronic Resource
    Electronic Resource
    The substrate specificity of uptake2 in the rat heart (1984)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 328 (1984), S. 164-173 
    Details
    ISSN: 1432-1912
    Keywords: Extraneuronal uptake ; Rat heart ; Catecholamines ; Stereoselectivity ; Substrate specificity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Experiments were carried out with hearts isolated from reserpine- and pargyline-pretreated rats; both noradrenaline-metabolizing enzymes and uptake1 were inhibited. Initial rates of extraneuronal uptake were measured after perfusion lasting for 2 min, either in the absence or in the presence of 100 μmol/l O-methyl-isoprenaline, a potent inhibitor of uptake2. 1. The ID50 (i.e., the concentration of unlabelled substance that halves the rate of uptake of a tracer concentration of 3H-(±)-isoprenaline) was determined for a variety of agents. Two types of stereoselective preference of (-)-isomers were observed: for isoprenaline and adrenaline (but not for noradrenaline)-and also for dobutamine. 2. The stereoselective preference for the (-)-isomers of isoprenaline and adrenaline is also evident from fluorimetric determination of initial rates of uptake of unlabelled isomers. 3. Experiments with various tritiated compounds indicate that uptake2 has a broad substrate spectrum: uptake2 is not restricted to 3H-catecholamines and 3H-phenethylamines, but extends to resorcinols (3H-orciprenaline), imidazoline derivatives (3H-clonidine), 3H-histamine and 3H-5-hydroxytryptamine (3H-5-HT). 4. Determinations of the V max of uptake2 revealed a correlation between the ID50 and the V max: the higher the ID50, the higher the V max. 5. These results indicate that uptake2 is a carrier-mediated process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00512067
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  • 8
    Electronic Resource
    Electronic Resource
    The outward transport of catecholamines mediated by uptake2 of the rat heart (1985)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 330 (1985), S. 203-211 
    Details
    ISSN: 1432-1912
    Keywords: Rat heart ; Extraneuronal efflux of catecholamines ; Carrier-mediated outward transport ; Uptake2 ; Facilitated exchange diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The efflux of3H-catecholamines from the extraneuronal tissue of the rat heart was analysed (after inhibition of vesicular and neuronal uptake, monoamine oxidase and catechol-O-methyl transferase). In most experiments, hearts were first loaded with a tracer concentration of a3H-catecholamine and then washed out. 1. For all four catecholamines [3H-(±)-isoprenaline,3H-(±)-adrenaline,3H-(−)-noradrenaline, and3H-dopamine] the loading period resulted in virtually the same distribution pattern: most of the radioactivity distributed into “compartment III”. However, the rate constants for efflux from compartment III increased in the order3H-(−)-noradrenaline 〈3H-dopamine〈3H-(±)-isoprenaline=3H-(±)-adrenaline. 2. O-methyl-isoprenaline (OMI, a potent inhibitor of uptake2) caused a concentration-dependent and partial inhibition of the efflux of all3H-catecholamines; its IC50 (half-maximal inhibition of OMI-sensitive efflux) was very close to that for half-maximal inhibition of inward transport by uptake2. It is concluded that there is not only (OMI-resistant) diffusional efflux of3H-catecholamines, but also (OMI-sensitive) outward transport of3H-catecholamines. The contribution by each of these processes to total efflux differed considerably from one3H-catecholamine to the next. 3. U-0521 (the COMT inhibitor used in this study) inhibited the OMI-sensitive efflux of3H-noradrenaline with an IC50 of about 100 μmol/l. However, no inhibitory effect was found for 10 μmol/l U-0521. 4. During the wash-out period (see above) various unlabelled substrates of uptake2 were added to the perfusion fluid at a concentration equalling 2×K m. Dopamine, which has a very highV max for uptake2, caused a small acceleration of the efflux of3H-isoprenaline (facilitated exchange diffusion); 5-hydroxytryptamine, which has an intermediateV max for uptake2, had no effect on the efflux of3H-isoprenaline; clonidine, which has a lowV max for uptake2, inhibited the efflux of3H-isoprenaline. 5. For a total of nine unlabelled substrates (added to the perfusion fluid at 2×K m) significant correlations were obtained between the degree of inhibition of the efflux of3H-(±)-isoprenaline, on the one hand, and the logarithm of either theV max or theK m for uptake2, on the other hand. Such results might be explained by either the dissociation of the substrate from the carrier on the inside or the return of the empty carrier to the outside being the rate-limiting step in the transport cycle. This would account for the differences betweenV max-values and for the inhibitory effect of substrates with lowV max for uptake2 on the efflux of3H-isoprenaline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00572435
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  • 9
    Electronic Resource
    Electronic Resource
    The handling of five amines by the extraneuronal deaminating system of the rat heart (1988)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 337 (1988), S. 159-163 
    Details
    ISSN: 1432-1912
    Keywords: Extraneuronal monoamine oxidase ; Uptake2 ; Rat heart ; Extraneuronal deaminating system ; Catecholamines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The handling of five amines by the extraneuronal deaminating system was studied in perfused hearts of rats (pretreated with reserpine; COMT and neuronal uptake inhibited). Hearts were perfused with 50 nmol/l 3H-noradrenaline for 30 min, in the presence of increasing concentrations of unlabelled (−)-adrenaline, (−)-noradrenaline, dopamine, tyramine and 5-HT. IC50's were determined as those concentrations of unlabelled amines which halved the steady-state rate of deamination of 3H-noradrenaline. After correction for changes in the tissue/medium ratio for 3H-noradrenaline, “half-saturating outside concentrations” were obtained. They increased in the order (−)-adrenaline (15 μmol/l) — tyramine — dopamine — noradrenaline —5-HT (53 μmol/l). The V max for extraneuronal deamination was determined for 3H-(−)-adrenaline, 3H-(−)-noradrenaline and 3H-dopamine, as well as (by HPLC and electrochemical detection) for tyramine and 5-HT. It was low for (−)-adrenaline, intermediate for (−)-noradrenaline, dopamine and 5-HT, high for tyramine. For the three catecholamines the half-saturating outside concentrations of the extraneuronal deaminating system clearly exceeded those for the extraneuronal O-methylating system of the same organ (see Grohmann and Trendelenburg 1985), although the two enzymes appear to co-exist in the same cells, so that the same transport system is involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169243
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  • 10
    Electronic Resource
    Electronic Resource
    Stereoselectivity of the accumulation and metabolism of noradrenaline in rabbit aortic strips (1978)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 302 (1978), S. 195-206 
    Details
    ISSN: 1432-1912
    Keywords: Stereoselectivity ; Noradrenaline ; Rabbit aorta ; MAO ; COMT
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Rabbit aortic strips were exposed to 1.18 μM 3H-(-)-or 14C-(+)-noradrenaline for 30 min. The accumulation and metabolism of noradrenaline were measured in some strips. In others the efflux of noradrenaline and its metabolites was measured during wash out with amine-free solution for 240–250 min. The following differences between the two isomers were observed: 1. No pronounced stereoselectivity existed for the extraneuronal and axoplasmic accumulation of noradrenaline. The vesicular accumulation and retention of noradrenaline was stereoselective when monoamine oxidase (MAO) was inhibited. 2. Neuronal and extraneuronal deamination of noradrenaline was clearly stereoselective [(-)〉(+)], extraneuronal O-methylation of the amine less so [(+)〉(-)], the latter probably as a consequence of the former. 3. Both in the neurone and in the extraneuronal tissue, more glycols were formed from (-)-than from (+)-noradrenaline, whereas about equal amounts of acid metabolites were formed from the two isomers. This was observed during the incubation and during wash out of the strips (i.e., during neuronal efflux). The degree of stereoselectivity increased when the concentration of noradrenaline was decreased to 0.118 μM. 4. The apparenthalf time for the late neuronal efflux of total radioactivity was (-)-〉(+)-noradrenaline, when storage vesicles were intact. After pretreatment with reserpine and after inhibition of MAO (i.e., when there was a pronounced axoplasmic accumulation of noradrenaline) the apparent half time for the late efflux of total radioactivity was subject to some stereoselectivity, but less so than when storage vesicles were intact. 5. The results indicate that vesicular storage as well as neuronal and extraneuronal MAO, aldehyde dehydrogenase and/or aldehyde reductase are stereoselective. 6. Comparison of efflux curves (present results) with relaxation curves (Trendelenburg, 1974) shows that, for equal rates of efflux of (-)-noradrenaline, the height of contraction was greater for extraneuronal than for neuronal efflux. It is likely that this difference is due to the morphology of the adrenergic innervation of the rabbit aorta.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00517986
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