ISSN:
1432-1912
Keywords:
Isoprenaline
;
Extraneuronal Uptake
;
Extraneuronal O-Methylation
;
Rat Heart
;
Removal of Isoprenaline
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary 1. Isolated rat and guinea-pig hearts were perfused with 0.95 μM (±)-isoprenaline or 3H(±)-isoprenaline, a catecholamine which is taken up by extraneuronal mechanisms only. From measurements of the arterio-nevous difference (by fluorimetry and by scintillation counting, respectively) the rate of removal of the amine from the perfusion fluid was measured; in addition, the rate of appearance of its metabolite (3-O-methyl-3H-isoprenaline; 3H-OMI) was determined in the venous effluent as well as the accumulation of 3H-isoprenaline and 3H-OMI in the heart. 2. Experiments with sodium thiocyanate and 14C-sorbitol showed that these agents distributed into the extracellular space (about 350 μl/g; t/2 for efflux of about 1.2 min) and into ventricular and atrial cavities (about 1500 μl/g; t/2 for efflux of 0.1 to 0.2 min). 3. The removal of 3H-isoprenaline from the perfusion fluid declined biphasically with time; after an initial rapid decline the rate of removal approached steadystate levels within about 30 min. After block of COMT (by the presence of 100 μM U-0521) the second phase of decline approached zero. In the absence of U-0521 the steady-state rate of removal was 10 times higher in rat than in guinea-pig hearts; in the presence of U-0521 the approach to zero was faster for guinea-pig than for rat hearts. 4. When COMT was intact, 3H-OMI appeared in the venous effluent, first at a rapidly increasing rate, from the 9th minute of perfusion onward at a steady rate which was identical with the steady-state rate of removal of 3H-isoprenaline. No 3H-OMI was detected after block of COMT. 5. The accumulation of 3H-isoprenaline in the heart reached a steady level within about 30 min; block of COMT increased the time required for approach to steady levels and increased the accumulation of 3H-isoprenaline in the rat (but not in the guinea-pig) heart. When COMT was intact, the accumulation of 3H-OMI in the heart reached steady-state levels within 10 min. 6. The time-dependent decline of the rate of removal of 3H-isoprenaline by hearts whose COMT had been inhibited was due to a time-dependent increase of the rate of efflux of the amine from the stores; there did not seem to be any change in the rate of gross influx. 7. Isoprenaline-induced ventricular fibrillation reduced the rate of O-methylation of 3H-isoprenaline significantly. 8. Perfusion of hearts with 0.095 μM (±)-isoprenaline resulted in a significantly greater accumulation of the amine in rat than in guinea-pig and rabbit hearts.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00501145
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