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

Autor: Trendelenburg, U., Fleig, H., Bryan, L., Bönisch, H.
Zdroj: Naunyn-Schmiedeberg's Archives of Pharmacology; 1983, Vol. 324 Issue 3, p169-179, 11p
Abstrakt: The distribution of H-isoprenaline in the perfused rat heart was re-examined. After initial loading with H-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 this department (Bönisch et al. 1974; Bönisch 1978), H-isoprenaline was found to distribute mainly into one extraneuronal 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 extraneuronal distribution compartment of H-isoprenaline has the characteristics of the 'old' compartment III: it has a relatively short half time for the efflux of H-isoprenaline and it has a high activity of COMT. Moreover, corticosterone inhibits the inward and outward flux of H-isoprenaline into and from compartment III. The K for the inhibition by corticosterone of the efflux of H-isoprenaline (2 μmol/l) is very similar to the K for impairment of uptake (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 H-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. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
Externí odkaz: