Biomedical subjects

U Trendelenburg

Publications and source records attributed to U Trendelenburg.

At least 19 recordsLinked to original sources

PubMed1992

The influence of the density of adrenergic innervation on the extracellular steady-state concentration gradient for 3H-noradrenaline.

After inhibition of extraneuronal uptake by corticosterone, isolated right atria and lengthwise halved vasa deferentia of the rat were incubated with 0.2 mumol/l 3H-noradrenaline for 60 min, washed out for 100 min and then prepared for autoradiography. The autoradiographic images were digitized, and silver grain density was determined as a function of the distance from the surface. Silver grain density declined towards the centre of the tissue; the decline was monophasic exponential and significantly steeper in the vas deferens (0.016 microns-1) than in the less densely innervated right atrium (0.011 microns-1). Silver grain density at the surface of the tissue was higher in vas deferens than in right atrium. The results show that the extracellular steady-state concentration gradient for 3H-noradrenaline (generated by uptake1 during the incubation with this amine) largely depends on the density of the adrenergic innervation.

Animals↗

PubMed1992

The force driving the extraneuronal transport mechanism for catecholamines (uptake2).

Recently, uptake2 was shown to exist in the clonal Caki-1 cell line. The aim of this study was two-fold: a) to determine, in Caki-1 cells, the intracellular fate of 3H-noradrenaline after its translocation by uptake2 and b) to analyse the force driving uptake2. Caki-1 cells have the characteristics of a "metabolizing system" in which the activity of catechol-O-methyl transferase (COMT) greatly exceeds that of monoamine oxidase (MAO). In all subsequent experiments these enzymes were inhibited. The determination of initial rates of uptake2 into Caki-1 cells at an extracellular pH between 6.9 and 7.9 indicated that the protonated species of 3H-noradrenaline is transported. Depolarization of Caki-1 cells (by three different procedures) inhibited the inward transport. Determination of the time course of the specific accumulation of 3H-noradrenaline in Caki-1 cells and of 3H-isoprenaline in the perfused rat heart (both mediated by uptake2) revealed that depolarization (by high K+) reduced the rate constant for inward transport (kIN) and increased that for outward movement (kOUT). Consequently, depolarization reduced the steady-state factor of accumulation. It is proposed that, as the protonated species of the substrates of uptake2 is transported, the membrane potential is likely to provide the driving force for uptake2. The fact that depolarization decreased kIN and increased kOUT agrees with this proposal, as do the magnitudes of the steady-state accumulation factors determined in Caki-1 cells and perfused rat heart.

Animals↗

PubMed1991

Energy requirements for the basal efflux of noradrenaline and its metabolites from adrenergic varicosities.

The combination of hypoxia plus glucose deprivation or of hypoxia plus lactate induces carrier-mediated outward transport of 3H-noradrenaline in the rat vas deferens. Lactate efflux is higher from atria than from vas deferens. Hence, the much lower contribution by outward transport to the spontaneous efflux of 3H-noradrenaline in vas deferens than atria is likely to be due to a better supply of oxygen (and perhaps also glucose) to the 3H-noradrenaline-storing varicosities in vas deferens than in atria.

Animals↗

PubMed1991

The steady-state concentration gradient for 3H-noradrenaline generated by uptake1 in the extracellular space of the rat vas deferens incubated with this amine.

The rat vas deferens was incubated with 0.2 mumol/l 3H-noradrenaline for 60 min, washed out with amine-free solution for 100 min and then prepared for autoradiography (same tissues as presented by Azevedo et al. (1990) Naunyn-Schmiedeberg's Arch Pharmacol 342:245-248). The autoradiographic images were then digitized, and grain density was determined as a function of the distance from the surface of the tissue. When neither monoamine oxidase nor vesicular uptake was impaired, i.e. under control conditions, grain density declined monophasically exponentially towards the centre of the tissue. Tis decline amounted to 0.017 micron-1 or 0.124 varicosity-1, since the average distance between varicosities was calculated to be 7.4 microns. After inhibition of monoamine oxidase and vesicular uptake the rate constant was significantly reduced, and the grain density in close proximity of the surface of the tissue was also reduced. It is proposed that the distribution of grain density observed in controls reflects the steady-state concentration gradient that is generated by uptake1 during the incubation with 3H-noradrenaline. During spontaneous efflux of 3H-noradrenaline one has to distinguish between "re-uptake of the 3H-amine into the leaking varicosity" and "uptake en passant" (during diffusion through the extracellular space). On the basis of the present results, the extent of "uptake en passant" was calculated (with a computer-assisted model) for the spontaneous efflux of heterogeneously distributed 3H-noradrenaline (after wash-out). "Uptake en passant" into varicosities located between the source of efflux and the medium amounted to about 55% of the net leakage of 3H-noradrenaline from all varicosities.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

The sensitivity of adrenergic varicosities to the 3H-noradrenaline-releasing effect of potassium.

After the loading of incubated, homogeneously innervated tissues with 3H-noradrenaline (monoamine oxidase and catechol-O-methyl transferase inhibited, calcium-containing solution) high K+ released the 3H-amine from adrenergic varicosities. In paired experiments the sensitivity of rat atria to high K+ exceeded that of vasa deferentia. In the rat vas deferens the releasing effect of high K+ was enhanced by drugs or procedures which induce a carrier-mediated outward transport of 3H-noradrenaline, i.e., by ouabain, by glucose deprivation and by hypoxia. In the presence of extracellular calcium desipramine failed to affect the releasing effect of high K+ (except in the absence of glucose or during hypoxia), but in the absence of calcium desipramine reduced it. Apparently, whenever the axoplasmic levels of 3H-noradrenaline are increased, high K+ is able to induce some carrier-mediated outward transport of the 3H-amine. It is suggested that "organ differences" with respect to the sensitivity to high K+ may well be due to hypoxia (plus some lack of glucose) of those varicosities that had been loaded with 3H-noradrenaline. The risk of storage of 3H-noradrenaline in hypoxic varicosities appears to be greater in incubated than in perfused organs, and in the former it is greater in sparsely than in densely innervated tissues.

Animals↗

PubMed1991

Carrier-mediated outward transport of dopamine from adrenergic varicosities of the vas deferens of reserpine-pretreated rats.

In vasa deferentia of reserpine-pretreated rats a carrier-mediated (i.e., desipramine-sensitive) outward transport of endogenous dopamine was induced by either tyramine or ouabain. The dopamine taking part in the efflux induced by tyramine (and the concomitant efflux of DOPAC) was derived from ongoing synthesis of dopamine. Inhibition of MAO trebled the rate of spontaneous efflux of dopamine and reduced the spontaneous efflux of DOPAC by 90%. After inhibition of MAO, desipramine caused a further five-fold increase in the basal efflux of dopamine with no change in the basal efflux of DOPAC. Inhibition of COMT failed to affect the spontaneous efflux of dopamine but increased that of DOPAC. It is concluded that, after depletion of the noradrenaline stores by pretreatment with reserpine, an outward transport of axoplasmic dopamine is induced by the same mechanisms that (without any pretreatment with reserpine) are known to initiate an outward transport of noradrenaline.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1991

The energy requirements for the basal efflux of 3H-noradrenaline from sympathetically innervated organs.

In the rat vas deferens (preloaded with 3H-noradrenaline, catechol-O-methyl transferase inhibited, calcium-free solution) ouabain, glucose deprivation or the combination of hypoxia plus presence of lactate were found to induce a carrier-mediated (desipramine-sensitive) outward transport of the 3H-amine. Glucose deprivation additionally increased the efflux of deaminated 3H-metabolites, as a consequence of an increased net leakage of vesicular 3H-noradrenaline; moreover, 3H-dihydroxymandelic acid then became the predominant neuronal metabolite. The simultaneous lack of oxygen and glucose resulted in a very pronounced release of the 3H-amine. Moreover, during spontaneous efflux more outward transport of 3H-noradrenaline was observed in the absence than in the presence of extracellular calcium. In rat atria (under the same experimental conditions) the contribution by carrier-mediated outward transport to the spontaneous efflux of tritium exceeded that in vasa deferentia. Moreover, the efflux of lactate (as an index of hypoxia of the tissue) exceeded that observed in vasa deferentia, under aerobic and anaerobic conditions. It is proposed that the greater contribution by outward transport of 3H-noradrenaline to spontaneous efflux in atria than in vasa deferentia does not reflect any basic difference between the varicosities in two different organs. It is likely that the less heterogeneous distribution of the 3H-amine in atria than in vasa deferentia is responsible for storage of the exogenous amine in atrial varicosities that are subject to some hypoxia, to an increased extracellular lactate level and to perhaps a minor degree of glucose deficiency; these factors may well be responsible for the difference with regard to outward transport of 3H-noradrenaline during spontaneous efflux. Thus, in addition to the heterogeneity of the distribution of 3H-noradrenaline, an additional heterogeneity with regard to the energy supply must be expected for incubated organs.

Animals↗

PubMed1991

The TiPS lecture: functional aspects of the neuronal uptake of noradrenaline.

For various amine transmitters (noradrenaline, dopamine, 5-HT) re-uptake into the releasing varicosity limits the transmitter's life span in the biophase. In the second TiPS Lecture, given at this year's FASEB meeting in Atlanta, Georgia, Ullrich Trendelenburg summarized the evidence relating to the function of the neuronal noradrenaline carrier (uptake1), why it is absolutely dependent on Na+ and Cl- and how it functions as a metabolizing system, hand in hand with intraneuronal monoamine oxidase and vesicular storage. This carrier clears noradrenaline from the extracellular space very efficiently. Hence, loading of incubated organs with exogenous substrates of uptake1 results in a very heterogeneous distribution of the amine. Moreover, under certain experimental and pathophysiological conditions the carrier is able to transport axoplasmic noradrenaline out of the varicosity, a 'release' mechanism operating, for instance, in cardiac ischaemia.

Animals↗

PubMed1990

The interaction of transport mechanisms and intracellular enzymes in metabolizing systems.

The life span of extracellular catecholamines is limited by the combination of uptake and subsequent intracellular metabolism by either monoamine oxidase (MAO) and/or catechol-O-methyl transferase (COMT). Three such "metabolizing systems" are involved in the inactivation of noradrenaline: 1) Neuronal uptake (high-affinity uptake1) in association with neuronal MAO (and vesicular uptake), 2) extraneuronal uptake (low affinity uptake2) in association with intracellular COMT and MAO (in smooth muscles, myocardial cells, glands), and 3) uptake1 of non-neuronal cells in association with intracellular COMT and/or MAO (in vascular endothelium of rat lung). Such systems function as "pump and leak systems with enzyme(s) inside". The analysis of either uptake or enzyme fails to reveal the characteristics of such systems; they are determined by the interaction of both components. Because of the high activity of these intracellular enzymes, it is unlikely that either COMT or MAO is ever saturated in vivo. However, in vitro saturation of extraneuronal COMT and MAO reveals that extraneuronal COMT is a high-affinity, but extraneuronal MAO a low-affinity enzyme. Hence, membrane-bound COMT appears to be responsible for the extraneuronal O-methylation of noradrenaline. If intracellular enzymes remain unsaturated, the determination of the rate constants describing the unsaturated enzyme (KENZYME = Vmax/Km) is of particular interest. KENZYME can be determined for metabolizing systems, since this rate constant is not affected by the (usually unknown) fractional size of the metabolizing system.

Animals↗

PubMed1990

Human Caki-1 cells are the first model for extraneuronal transport of noradrenaline (uptake2) which is based on a clonal cell line.

The neurotransmitter noradrenaline is inactivated by active transport out of the synaptic cleft--either back into the adrenergic neuron or into extraneuronal cells. Transport studies on isolated cells provide many advantages. However, an experimental model for the extraneuronal uptake of noradrenaline which is based on a clonal cell line was not known until now. The human renal carcinoma cell line Caki-1 is the first clonal cell line known to express the extraneuronal transport system for noradrenaline.

Animals↗

PubMed1990

The heterogeneity of the neuronal distribution of exogenous noradrenaline in the rat vas deferens.

After loading of the incubated rat vas deferens with 0.2 mumol/l 3H-noradrenaline (followed by 100 min of wash-out with amine-free solution), the efflux of endogenous and exogenous compounds was determined by HPLC with electrochemical detection and by column chromatography with scintillation counting. Two different types of heterogeneity of labelling were found. The first one is due to the preferential labelling of varicosities close to the surface of the tissue, the second one to the preferential labelling of vesicles close to the surface of loaded varicosities. As diffusion distances within the tissue and within varicosities are then longer for endogenous than for exogenous amine and metabolites, the composition of spontaneous efflux of exogenous compounds differed from that for endogenous compounds. Because of preferential neuronal and vesicular re-uptake of endogenous noradrenaline, the percentage contribution by noradrenaline to overall efflux was: endogenous less than exogenous. While 3H-DOPEG was the predominant exogenous metabolite, DOPEG and MOPEG equally contributed to the "endogenous" efflux. Desipramine abolished the consequences of the first heterogeneity of labelling, i.e., it increased the efflux more for endogenous than for exogenous noradrenaline; moreover it decreased the efflux of 3H-DOPEG, but increased that of 3H-MOPEG. The reserpine-like compound Ro 4-1284, on the other hand, abolished the consequences of the second type of heterogeneity; it reduced the specific activity of "total efflux" (i.e., of the sum of noradrenaline + DOPEG + MOPEG) to the specific activity of the tissue noradrenaline. The degree of heterogeneity of labelling was reduced after inhibition of monoamine oxidase and also when the tissues were loaded with 2 or 20 mumol/l 3H-noradrenaline. It is proposed that the various "compartments" and "pools" of noradrenaline described in the literature reflect the two heterogeneities described here.

2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-↗

PubMed1990

Autoradiographic study of the rat vas deferens incubated with 3H-noradrenaline.

Rat vasa deferentia were incubated with 0.2 mumol/l 3H-noradrenaline for 60 min and then washed out with amine-free solution for 100 min. Autoradiography then revealed a preferential labelling of the varicosities in the immediate vicinity of the surface of the tissue. However, when tissues were obtained from reserpine- and pargyline-pretreated rats (to block vesicular uptake and monoamine oxidase), 3H-noradrenaline was able to penetrate more deeply into the tissue. These differences are in accordance with the view that the autoradiographs reflect the 3H-noradrenaline concentration gradient (within the extracellular space) generated by the neuronal uptake of the 3H-amine; the concentration gradient is steeper (and the heterogeneity of labelling is more pronounced) in tissues with intact vesicular uptake and monoamine oxidase than in tissues in which these mechanisms had been inhibited.

Animals↗

PubMed1989

The uptake and metabolism of 3H-catecholamines in rat cerebral cortex slices.

The accumulation and metabolism of 3H-catecholamines were studied in cerebral cortex slices obtained from rats pretreated with reserpine, during 30 min of incubation with 50 nmol/l of the 3H-amines. In some experiments neuronal uptake (uptake1) was inhibited by the presence of 0.3 mumol/l desipramine, in others COMT was inhibited by 30 mumol/l U-0521. When both MAO and COMT were intact, most of the metabolism of 3H-noradrenaline was neuronal (i.e., desipramine-sensitive). For 3H-adrenaline rates of neuronal metabolism were much lower than for 3H-noradrenaline, non-neuronal O-methylation accounting for about 50% of total metabolism. Rates of metabolism of 3H-dopamine were similar to those of 3H-noradrenaline, but with a predominance of non-neuronal metabolism, which involved O-methylation and deamination. - Under these conditions, very little 3H-catecholamine was recovered from the tissues; moreover, desipramine tended to increase tissue levels. Hence, tissue content then appears to partly reflect extracellularly distributed 3H-amines. After block of MAO rates of metabolism of 3H-noradrenaline and 3H-dopamine were greatly reduced, and tissue levels were increased. Desipramine now antagonized the accumulation of 3H-amines in the tissue, while U-0521 increased it. Rates of O-methylation (in the presence of desipramine) increased in the order 3H-noradrenaline less than 3H-dopamine. It is concluded that neuronal uptake is associated with MAO only, and rates of neuronal deamination increased in the order: 3H-adrenaline less than 3H-dopamine much less than 3H-noradrenaline.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

The extent of neuronal re-uptake of 3H-noradrenaline in isolated vasa deferentia and atria of the rat.

After pretreatment of rats with reserpine and pargyline (to inhibit vesicular uptake and monoamine oxidase, respectively) and after inhibition of catechol-O-methyl transferase (by U-0521) and in calcium-free solution, the adrenergic neurones of isolated vasa deferentia and atria were loaded with 3H-noradrenaline. The spontaneous efflux of 3H-noradrenaline and 3H-dihydroxyphenylglycol was determined, as well as the steady-state effect of two concentrations of desipramine. On the basis of a mathematical model of the adrenergic nerve ending, fractional rates (FR = rate of flux divided by tissue tritium content) were calculated for unidirectional outward diffusion, for outward transport and for neuronal re-uptake (all for 3H-noradrenaline). Although the density of adrenergic innervation is lower in atria than in vasa deferentia, neuronal re-uptake amounted to about 90% of the spontaneous efflux of 3H-noradrenaline in both tissues. While the FR for unidirectional outward diffusion was virtually the same in both tissues, the FR for outward transport of 3H-noradrenaline was more than three times higher in atria than in vasa deferentia. There is, as yet, no explanation for this pronounced difference.

Animals↗

PubMed1989

The release of 3H-noradrenaline by p- and m-tyramines and -octopamines, and the effect of deuterium substitution in alpha-position.

The 3H-noradrenaline-releasing effects of p- and m-tyramines and -octopamines, either deuterated or not, were studied in isolated vasa deferentia of the rat (COMT inhibited and calcium-free solution in all experiments). Km for uptake1 was higher for octopamines than for tyramines, but not increased by the introduction of deuterium in alpha-position, except for (probably contaminated) deuterated p-octopamine. Other tissues were preloaded with 3H-noradrenaline. After inhibition of vesicular uptake and MAO equi-releasing concentrations of the eight amines were strictly correlated with Km, they were 6 to 7 times higher for unsubstituted octopamines than for corresponding tyramines. When only MAO (but not vesicular uptake) was inhibited, this difference decreased to about 4-fold, but the releasing potency of the deuterated amines (relative to their parent amines) remained unchanged (except for p-octopamine). When vesicular uptake and MAO were intact, unsubstituted octopamines were only 1.5 to 2.2 times less potent than the corresponding tyramines. Analysis of the efflux of 3H-DOPEG confirmed that this gain in the relative potencies of octopamines is due to their increased ability to mobilize vesicular 3H-noradrenaline; moreover, deuterated amines as well were then better mobilizers than were their parent amines. It is concluded that, provided vesicular uptake is intact, the introduction of a beta-OH-group enhances the ability of indirectly acting sympathomimetic amines to mobilize vesicular noradrenaline; the introduction of deuterium in alpha-position, on the other hand, enhances this mobilizing effect exclusively when MAO is intact.

2-Hydroxyphenethylamine↗

PubMed1988

The handling of five amines by the extraneuronal deaminating system of the rat heart.

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 mumol/l) - tyramine - dopamine - noradrenaline - 5-HT (53 mumol/l). The Vmax 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.

Animals↗

PubMed1988

The uptake and O-methylation of 3H-(+/-)-isoprenaline in rat cerebral cortex slices.

The O-methylation and accumulation of 3H-isoprenaline in slices of the rat cerebral cortex were studied before and after inhibition of COMT. 1. Inhibition of COMT by 30 mumol/l U-0521 virtually abolished the O-methylation and increased the accumulation of 3H-isoprenaline; hence, there is evidence for the existence of a central O-methylating system (with a transport mechanism and intracellular COMT). 2. Experiments were carried out with selective uptake inhibitors for uptake1 (cocaine and desipramine) or uptake2 (corticosterone and OMI), with phenoxybenzamine (known to inhibit both carriers) and with changes in the ionic composition of the incubation medium. They revealed that the central carrier differed from both, uptake1 and uptake2, although exhibiting some resemblance with uptake2 (lack of dependence on Na+ and Cl-, sensitivity to K+ and phenoxybenzamine, ability to transport 3H-isoprenaline). 3. Although the central carrier was rather sensitive to inhibition by beta-adrenoceptor antagonists (propranolol, carteolol), the effect of propranolol was not stereoselective; hence, beta-adrenoceptors do not seem to be involved. 4. Virtually identical IC30-values were obtained for inhibitors, when determined with or without inhibition of COMT. Only OMI was found to inhibit COMT as well as the central transport system; hence it was more potent in inhibiting the O-methylation than the accumulation of 3H-isoprenaline. 5. IC50-values (against initial rates of accumulation of 3H-isoprenaline; COMT inhibited) were determined for various substrates and inhibitors of peripheral uptake2. There was no correlation with the IC50-values determined earlier for uptake2 in rat heart (Grohmann and Trendelenburg 1984).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

The functional coupling of neuronal and extraneuronal transport with intracellular monoamine oxidase.

"Metabolizing systems" are responsible for the quick inactivation of noradrenaline released from adrenergic nerve endings: a transport mechanism (uptake1 or uptake2) is arranged in series with the intracellular enzyme (monoamine oxidase, MAO; catechol-O-methyltransferase, COMT). In the perfused rat heart, kenzyme-values were determined, i.e., those rate constants which characterize the unsaturated intracellular enzymes. In the extraneuronal metabolizing system kcomt greater than kmao for noradrenaline and adrenaline, while rather similar rate constants were obtained for dopamine. However, for the neuronal deaminating system, kmao is considerably higher than kmao for the extraneuronal system. Second, in the rat vas deferens it is demonstrated that inhibition of neuronal MAO leads to very pronounced rises of the axoplasmic noradrenaline concentration--and this is again a reflection of the high activity of neuronal MAO. In a third series of experiments (with the rat vas deferens), the evidence indicates that the neuronal inward transport of substrates of MAO fails to saturate the enzyme. This is the functional consequence of the high activity of neuronal MAO. It is concluded that a) neuronal MAO activity is very high, and--as a consequence--b) axoplasmic noradrenaline levels are very low.

Animals↗