ISSN:
1432-1912
Keywords:
Indirectly acting sympathomimetic amines
;
Tyramine
;
Octopamine
;
Deuterium in α-position
;
Rat vas deferens
;
Noradrenaline outward transport
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The3H-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). K m, for uptake1 was higher for octopamines than for tyramines, but not increased by the introduction of deuterium in α-position, except for (probably contaminated) deuterated p-octopamine. Other tissues were preloaded with3H-noradrenaline. After inhibition of vesicular uptake and MAO equi-releasing concentrations of the eight amines were strictly correlated withK m, 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 of3H-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 \-OH-group enhances the ability of indirectly acting sympathomimetic amines to mobilize vesicular noradrenaline; the introduction of deuterium in α-position, on the other hand, enhances this mobilizing effect exclusively when MAO is intact.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00736058
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