ISSN:
1432-1912
Keywords:
3H-Catecholamines
;
Perfused rat heart
;
Stereoselectivity
;
Extraneuronal O-methylating system
;
Catechol-O-methyl transferase
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary In a comparative study, the handling of five catecholamines by the extraneuronal O-methylating system of the rat heart was determined; all rats were pretreated with reserpine, monoamine oxidase and neuronal uptake were inhibited in all experiments. 1. Hearts were perfused for 7 min with a tracer concentration of 3H-(±)-isoprenaline, either in the absence or in the presence of unlabelled catecholamines (which reduced the O-methylation of the tracer amine). IC50's were determined for unlabelled catecholamines and then converted to “half-saturating outside concentrations”, i.e., to those concentrations in the perfusion fluid that halfsaturate the intracellular catechol-O-methyl transferase (COMT). The values for the (-)-isomers of dobutamine, isoprenaline, adrenaline and noradrenaline and that for dopamine were low and rather similar (between 0.67 and 2.7 μmol/l). Stereoselectivity for isoprenaline probably reflected the preference of uptake2 for the (-)-isomer. 2. The effects of (-)- and (+)-dobutamine indicated that both isomers are a) transported by uptake2 and b) good substrates of COMT. 3. The V max for O-methylation [determined for 3H-(±)-isoprenalina, 3H-(±)-adrenaline, 3H-(±)-noradrenaline and 3H-dopamine] was rather similar for all four catecholamines. 4. It is concluded that the extraneuronal O-methylating system of the rat heart handles the five catecholamines in a similar manner, although the K m for uptake2 had been found to increase substantially in the order: dobutamine 〈 isoprenaline 〈 adrenaline 〈 noradrenaline 〈 dopamine (Grohmann and Trendelenburg 1984b).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00501878
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