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Biomedical subjects

U Trendelenburg

Publications and source records attributed to U Trendelenburg.

At least 55 records · Page 3Linked to original sources
PubMed1984

Kinetics of the O-methylating system for isoprenaline in the trachea and aorta of rabbit.

Segments of tracheal smooth muscle or aorta from rabbits pretreated with reserpine (1 mg/kg) were incubated in 3H-isoprenaline (0.5-60 mumol/l). Steady-state rates of O-methylation were determined by measuring the formation of 3-O-methylisoprenaline (OMI) after incubation of tracheal and aortic tissues for 30 min and 10 min, respectively. The steady-state O-methylation of isoprenaline in rabbit trachea was saturable, at least up to 60 mumol/l isoprenaline. In rabbit aorta, the O-methylation appeared to be saturable up to 30 mumol/l isoprenaline, but the rate of O-methylation increased for higher concentrations. The Km values for the saturable component of O-methylation were 11.8 mumol/l in trachea and 3.03 mumol/l in aorta. The Vmax values were 0.51 nmol X g-1 X min-1 in trachea and 0.56 nmol X g-1 X min-1 in aorta. In tissues incubated in 0.5 mumol/l isoprenaline, 100 mumol/l corticosterone caused 78% inhibition of OMI formation in trachea and 86% inhibition in aorta. There was no inhibition of OMI formation by 100 mumol/l corticosterone in tracheal or aortic tissues incubated in 60 mumol/l isoprenaline. Model calculations showed that the experimental results in trachea and aorta (3. above) were consistent with (a) entry of isoprenaline into the cells in the tissues by extraneuronal uptake and diffusion, and (b) exposure of the isoprenaline to intracellular catechol-O-methyltransferase with Vmax enzyme much less than Vmax uptake.

Animals↗
PubMed1984

The outward transport of axoplasmic noradrenaline induced by a rise of the sodium concentration in the adrenergic nerve endings of the rat vas deferens.

The adrenergic nerve endings of the rat vas deferens were loaded with 3H-(-)-noradrenaline; COMT was inhibited by the presence of 10 mumol/l U-0521, and all experiments were carried out with calcium-free solution. After 100 min of wash-out a neuronal efflux of tritium was obtained which remained constant with time (when expressed as fractional rate of loss; FRL); it contained more DOPEG than noradrenaline. The in vitro administration of reserpine-like drugs (reserpine and Ro 4-1284) increased the FRL of tritium, presumably because of an increase in the leakage of noradrenaline from storage vesicles; the efflux of DOPEG increased more than that of noradrenaline, and the ratio NA/DOPEG declined. Inhibition of the membrane ATPase (by omission of potassium from the medium or by the presence of 3 mmol/l ouabain) increased the FRL of tritium, presumably because of an increase in the net leakage of noradrenaline from the storage vesicles (as a consequence of the fall in the concentration of free axoplasmic noradrenaline; see below). Veratridine also increased the FRL of tritium, partly because of its known reserpine-like effect (Bönisch et al. 1983); in the presence of 1 mumol/l veratridine, the efflux of DOPEG increased. Irrespective of the presence or absence of reserpine or Ro 4-1284, inhibition of the membrane ATPase or the presence of veratridine (agents or procedures which increase the axoplasmic sodium concentration) always resulted in a brisk increase of the efflux of noradrenaline that was accompanied by a simultaneous decrease in the efflux of DOPEG (see above for one exception).(ABSTRACT TRUNCATED AT 250 WORDS)

2H-Benzo(a)quinolizin-2-ol, 2-Ethyl-1,3,4,6,7,11b-↗
PubMed1984

The influence of inhibition of catechol-O-methyl transferase or of monoamine oxidase on the extraneuronal metabolism of 3H-(-)-noradrenaline in the rat heart.

The extraneuronal metabolism of 3H-(-)-noradrenaline (1 nmol/l) was determined in rat hearts obtained from reserpine-pretreated animals (in the presence of 30 mumol/l cocaine). Inhibition of monoamine oxidase (MAO) (by pretreatment of the animals with pargyline) increased the formation of O-methylated metabolites by nearly that amount by which the formation of deaminated metabolites declined; hence, catechol-O-methyl transferase (COMT) seemed to be able to nearly fully compensate for the loss of MAO activity. However, when COMT was inhibited (by the presence of either 1 or 10 mumol/l U-O521), the increase in the formation of deaminated metabolites was smaller than the decrease in the formation of O-methylated metabolites; hence, MAO seemed to be unable to fully compensate for the loss of COMT activity. These results are discussed with regard to the hypothesis that the two extraneuronal enzymes co-exist in one compartment. As inhibition of COMT causes a much greater increase in the steady-state tissue/medium ratio for 3H-(-)-noradrenaline than does inhibition of MAO, it is suggested that it is this increase in the intracellular concentration of 3H-(-)-noradrenaline which - by promoting an efflux of the unchanged amine that is proportional to the tissue/medium ratio - actually decreases the net removal of 3H-(-)-noradrenaline from the perfusion fluid. The results are compatible with (but no evidence for) the hypothesis that the two enzymes co-exist in the same extraneuronal compartment.

Animals↗
PubMed1984

Saturation of monoamine oxidase by intraneuronal noradrenaline accumulation.

After pretreatment of the rats with reserpine and pargyline (to inhibit vesicular uptake and MAO), after an additional in vitro treatment with pargyline, and in the presence of U-0521 (to inhibit COMT), the adrenergic nerve endings of vasa deferentia were loaded with 3H-(-)-noradrenaline by exposure to various concentrations of this amine. Subsequently, tissues were washed out with amine-free solution, and the neuronal efflux of tritium was analysed. During 180 min of wash-out the apparent rate constant for the efflux of tritium decreased with increasing tritium content of the tissue. Prolongation of the wash-out period to 305 min revealed that efflux curves for tritium from heavily loaded tissues became steeper after the 180th min of wash-out. This phenomenon is indicative of saturation (followed by desaturation) of a process that limits the efflux of tritium from heavily loaded tissues. Analysis of the radioactivity of the efflux revealed a characteristic efflux curve for DOPEG: the formation of DOPEG appears to be saturated when the 3H-(-)-noradrenaline content of the tissue is high, in order to become desaturated during prolonged wash-out. These results cannot distinguish between MAO and alcohol dehydrogenase as the saturable enzyme. The formation of the mainly deaminated metabolites (during 60 min of wash-out) was determined in lightly and in heavily loaded tissues. The ratio "formation of metabolites/3H-(-)-noradrenaline content" was lower in heavily than in lightly loaded tissues; the relative decline in DOPEG formation was not accompanied by a compensatory increase in the formation of DOMA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

The substrate specificity of uptake2 in the rat heart.

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 mumol/l O-methyl-isoprenaline, a potent inhibitor of uptake2. 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. The stereoselective preference for the (-)-isomers of isoprenaline and adrenaline is also evident from fluorimetric determination of initial rates of uptake of unlabelled isomers. 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). Determinations of the Vmax of uptake2 revealed a correlation between the ID50 and the Vmax: the higher the ID50, the higher the Vmax. These results indicate that uptake2 is a carrier-mediated process.

Animals↗
PubMed1983

The extraneuronal compartments for the distribution of isoprenaline in the rat heart.

The distribution of 3H-isoprenaline in the perfused rat heart was re-examined. After initial loading with 3H-isoprenaline hearts were washed out with amine-free solution; the efflux curves were subjected to the peeling technique, and half times for efflux and compartment sizes were determined. In contrast to earlier reports from his department (Bönisch et al. 1974;l Bönisch 1978), 3H-isoprenaline was found to distribute mainly into one extra-neuronal compartment, irrespective of whether COMT was intact or inhibited (by the presence of U-0521). It was also not influenced by pretreatment of the animals with reserpine. This type of distribution was influenced neither by the concentration of isoprenaline nor by the duration of the loading of the tissue with the amine. The one major extra-neuronal distribution compartment of 3H-isoprenaline has the characteristics of the "old" compartment III: it has a relatively short half time for the efflux of 3H-isoprenaline and it has a high activity of COMT. Moreover, corticosterone inhibits the inward and outward flux of 3H-isoprenaline into and from compartment III. The Ki for the inhibition by corticosterone of the efflux of 3H-isoprenaline (2 mumol/l) is very similar to the Ki for impairment of uptake2 (determined by Bönisch 1978). Apart from the major distribution compartment III, two minor distribution compartments were detected: On the one hand, experiments with hearts which had an intact COMT revealed that a minor distribution compartment IV (characterized by a long half time for efflux and by an absence of COMT activity) may exist, although its magnitude does not exceed one tenth of the former compartment IV. In addition, part of the quickly equilibrating (and rather small) compartment II was corticosterone-sensitive. When the results of Azevedo et al. (1983 are considered together with the present results, compartment III appears to represent the uptake of 3H-isoprenaline into myocardial cells, while it is likely that radioactivity accumulated in the smooth muscle of blood vessels may constitute the corticosterone-sensitive part of compartment II.

Animals↗
PubMed1983

The isotope effect of tritium in 3H-(-)-adrenaline with very high specific activity.

Initial rates of the extraneuronal uptake of 3H-(-)-adrenaline of very high specific activity were determined in the perfused rat heart, fluorimetrically for unlabelled and by scintillation counting for labeled amine. The presence of nearly four tritium substituents in the adrenaline molecule slowed uptake by a factor of 5.56. The isotope effect of tritium appears to increase in direct proportion to the number of tritium substituents per molecule. It is concluded that 3H-catecholamines of very high specific activity are unsuitable for studies of the uptake and metabolism of 3H-catecholamines.

Animals↗
PubMed1983

Autoradiographic study of rat hearts perfused with 3H-isoprenaline.

Bönisch et al. (1974) identified kinetically two extraneuronal compartments into which 3H-isoprenaline distributes in the perfused rat heart: compartment III (characterized by a half time for the efflux of 3H-isoprenaline of about 10 min) had about the same size as compartment IV (half time for efflux: 23 min). These authors suggested that compartment III might be located in the vascular smooth muscle, while compartment IV might be located in myocardial cells. The present study was carried out to validate or refute this suggestion. Rat hearts were perfused for 5, 20 or 60 min with 1 mumol/l 3H-isoprenaline; additional hearts were perfused with 1 mumol/l 3H-isoprenaline for 30 min in the presence of either 20 mumol/l corticosterone or 20 mumol/l corticosterone plus 30 mumol/l cocaine. COMT was inhibited in all experiments (by the presence of 100 mumol/l U-0521). Quantitative autoradiography revealed in all groups that the silver grain density (grains/mm2) was greater over small blood vessels (arterioles and venules) than over myocardial cells. However, total silver grains over myocardial cells greatly exceeded those over small blood vessels (by a factor of 6 to 9). Thus, the suggestion of Bönisch et al. (1974) is untenable. Autoradiographic results obtained with small specimens of ventricular muscle are representative of the whole heart, since "silver grains over total tissue" (per mm2) were highly significantly correlated with the 3H-isoprenaline content of the homogenized hearts (in pmol/g). While corticosterone reduced the accumulation of 3H-isoprenaline in myocardial cells, it failed to affect the appearance of silver grains over Purkinje cells. However, cocaine prevented this type of accumulation. Thus, uptake in Purkinje cells appears to resemble neuronal rather than extraneuronal uptake.

Animals↗
PubMed1980

The neuronal and extraneuronal uptake and deamination of 3H-(-)-phenylephrine in the perfused rat heart.

The neuronal and extraneuronal uptake and deamination of 3H-(-)-phenylephrine was studied in perfused rat hearts obtained from reserpine-pretreated animals. 1. Under the conditions of steady-state perfusion with 5 mumol/l 3H-(-)-phenylephrine slightly more than 50% of total deamination took place in adrenergic nerve endings, slightly less than 50% in the extraneuronal tissue. 2. 3H-(-)-phenylephrine is preferentially deaminated to the glycol metabolite. 3. There is pronounced non-saturable, cocaine- and corticosterone-resistant uptake of 3H-(-)-phenylephrine in the perfused rat heart. 4. The apparent rate constants for the efflux of the glycol metabolite is about 20 times higher than that for the efflux of the acid metabolite. 5. For both the glycol and the acid metabolite of 3H-(-)-phenylephrine, apparent rate constants for the efflux declined when the duration of the perfusion with the labelled parent amine was prolonged. This phenomenon was also observed when the deamination of 3H-(-)-phenylephrine was restricted to either the adrenergic nerve endings or the extraneuronal tissue. These results are interpreted as evidence for a distribution of each metabolite into at least two kinetically different compartments. 6. This was confirmed for the acid metabolite by determination of a biphasic efflux curve in wash-out experiments in which MAO was inhibited during wash-out (after an initial loading of the adrenergic nerve endings with 3H-(-)-phenylephrine).

Animals↗
PubMed1980

A mathematical model representing the extraneuronal O-methylating system of the perfused rat heart.

1. A mathematical model was developed to mimic the function of the extraneuronal O-methylating system of the rat heart. Its essential features are: a saturable uptake process (uptake 2), a saturable, intracompartmental enzyme (COMT), the ability of the catecholamine to penetrate the membrane of the model compartment by a diffusional flux obeying first-order kinetics, and the ability of the metabolite to leave the compartment by an efflux obeying first-order kinetics. 2. Of the six kinetic constants of the model compartment five are known from experiments with hearts perfused with 3H-isoprenaline (Kmuptake, Vmaxuptake, Vmaxenzyme, k for amine, k for metabolite); only one constant is unknown (Kmenzyme) for the intact heart cells. 3. Results calculated with the help of the mathematical model were compared with results obtained from rat hearts perfused with 3H-isoprenaline. Although full congruency of results cannot be expected, there was satisfactory agreement between the two sets of results. Apparently, the mathematical model is able to simulate the function of the O-methylating system of the rat heart. 4. Comparison of the two sets of results leads to a definition of the function of the O-methylating system of the perfused rat heart. if all cells of the rat heart participate in the O-methylating system, the Km of the COMT of intact heart cells must be very low (i.e., somewhere between 2 and 5 microM isoprenaline). However, if the O-methylating system comprises only a small fraction of all cells, the COMT of the intact heart cells may well have a correspondingly higher Km.

Animals↗