Analysis of the compartments involved in the extraneuronal storage and metabolism of isoprenaline in the perfused heart
- 22 Downloads
Rat hearts were perfused with various concentrations of 3H-(±)-isoprenaline, and initial rates were determined for the removal of the amine from the perfusion fluid and for its O-methylation. Both removal and O-methylation obeyed Michaelis-Menten kinetics, K m and Vmax being 21 μM and 38 nmoles · g−1 · min−1 for the former, and 2.9 μM and 1.7 nmoles · g−1 · min−1 for the latter. After block of COMT the kinetic constants for removal (which equals accumulation under these conditions) were about the same as before. The kinetics of O-methylation seem to differ strikingly from those of accumulation of unchanged amine.
Corticosterone and 3-O-methylisoprenaline were about equipotent in antagonizing the accumulation and O-methylation of isoprenaline in the rat heart during perfusion with 3H-isoprenaline.
U-0521 (dihydroxy-2-methyl propiophenone; 100 μM) was used as a blocker of COMT. In addition it was found to be a weak inhibitor of the extraneuronal uptake of isoprenaline (K i =230 μM).
After block of COMT and subsequent to perfusion of the heart with 0.95 μM 3H-isoprenaline, efflux curves were determined during wash out with amine-free solution. Four compartments were detected (in order of increasing half time of efflux): I represented the fluid in dead space, cardiac cavities and large vessels; II equalled the extracellular space; III and IV represented extraneuronal storage sites. Corticosterone impaired the filling of compartments III and IV when present during filling. Both corticosterone and 3-O-methylisoprenaline (OMI) delayed the efflux from compartment III when present in the wash out solution only.
Experiments with guinea-pig hearts showed qualitative similarities between these and rat hearts. However, the storage and the O-methylating capacity of the guinea-pig heart was considerably smaller than that of the rat heart.
Rat ventricle slices (exposed to 0.95 μM 3H-(±)-isoprenaline for 30 min) were compared with perfused hearts. While the accumulation of 3H-isoprenaline was about 1/4, the total formation of 3H-OMI was only 1/50 of that determined for the perfused heart. This low rate of formation of 3H-OMI was also observed for slices of aorta, vas deferens and spleen, while slices of salivary glands had a high O-methylating capacity. Apparently, perfusion of the heart provides optimal access to the O-methylating compartment which may be located in vascular smooth muscle.
Key wordsIsoprenaline Extraneuronal COMT Uptake2 Corticosterone Extraneuronal Compartments
Unable to display preview. Download preview PDF.
- Almgren, O., Jonason, J.: Relative importance of neuronal and extraneuronal mechanisms for the uptake and retention of noradrenaline in different tissues of the rat. Naunyn-Schmiedebergs Arch. Pharmak. 270, 289–309 (1971)Google Scholar
- Bönisch, H., Trendelenburg, U.: Extraneuronal removal, accumulation and O-methylation of isoprenaline in the perfused heart. Naunyn-Schmiedeberg's Arch. Pharmacol. 283, 191–218 (1974)Google Scholar
- Bönisch, H., Uhlig, W.: Uptake and metabolism of isoprenaline in the isolated perfused heart of the rat and guinea pig. Naunyn-Schmiedeberg's Arch. Pharmacol. 277, R 6 (1973)Google Scholar
- Callingham, B. A., Burgen, A. S. V.: The uptake of isoprenaline and noradrenaline by the perfused rat heart. Molec. Pharmacol. 2, 37–42 (1966)Google Scholar
- Dick, D. A. T., Lea, E. J. A.: Na fluxes in single toad oocytes with special reference to the effect of external and internal Na concentration on Na efflux. J. Physiol. (Lond.) 174, 55–90 (1964)Google Scholar
- Dixon, M.: The determination of enzyme inhibitor constants. Biochem. J. 55, 170–171 (1953)Google Scholar
- Dixon, M., Webb, E. C.: Enzymes, 2nd ed. London: Longmans Ltd 1964Google Scholar
- Eisenfeld, A. J., Axelrod, J., Krakoff, L.: Inhibition of the extraneuronal accumulation and metabolism of norepinephrine by adrenergic blocking agents. J. Pharmacol. exp. Ther. 156, 107–113 (1967a)Google Scholar
- Eisenfeld, A. J., Landsberg, L., Axelrod, J.: Effect of drugs on the accumulation and metabolism of extraneuronal norepinephrine in the rat heart. J. Pharmacol. exp. Ther. 158, 378–385 (1967b)Google Scholar
- Graefe, K. H., Trendelenburg, U.: Hydrocortisone-induced supersensitivity to noradrenaline in the isolated nictitating membrane as a consequence of an impairment of an O-methylating system with high affinity. Naunyn-Schmiedeberg's Arch. Pharmacol. 282, R 26 (1974)Google Scholar
- Hellmann, G., Hertting, G., Peskar, B.: Uptake kinetics and metabolism of 7-3H-dopamine in the isolated perfused rat heart. Brit. J. Pharmacol. 41, 256–269 (1971)Google Scholar
- Iversen, L. L.: The uptake of catechol amines at high perfusion concentrations in the rat isolated heart: A novel catechol amine uptake process. Brit. J. Pharmacol. 25, 18–33 (1965)Google Scholar
- Iversen, L. L., Salt, P. J.: Inhibition of catecholamine uptake2 by steroids in the isolated rat heart. Brit. J. Pharmacol. 40, 528–530 (1970)Google Scholar
- Jacobowitz, D., Brus, R.: A study of extraneuronal uptake of norepinephrine in the perfused heart of the guinea-pig. Europ. J. Pharmacol. 15, 274–284 (1971)Google Scholar
- Jarrott, B.: Uptake and metabolism of catecholamines in the perfused hearts of different species. Brit. J. Pharmacol. 38, 810–821 (1970)Google Scholar
- Kaumann, A. J.: Adrenergic receptors in heart muscle: relations among factors influencing the sensitivity of the cat papillary muscle to catecholamines. J. Pharmacol. exp. Ther. 173, 383–398 (1970)Google Scholar
- Kaumann, A. J.: Potentiation of the effects of isoprenaline and noradrenaline by hydrocortisone in cat heart muscle. Naunyn-Schmiedeberg's Arch. Pharmacol. 273, 134–153 (1972)Google Scholar
- Langer, S. Z., Stefano, F. J. E., Enero, M. A.: Pre- and postsynaptic origin of the norepinephrine metabolites formed during transmitter release elicited by nerve stimulation. J. Pharmacol. exp. Ther. 183, 90–102 (1972)Google Scholar
- Mireylees, S. E., Foster, R. W.: 3-Methoxyisoprenaline: a potent selective uptake2 inhibitor. J. Pharm. Pharmacol. 25, 833–835 (1973)Google Scholar
- Osswald, W., Branco, D.: The effects of drugs and denervation on removal and accumulation of noradrenaline in the perfused hind-limb of the dog. Naunyn-Schmiedeberg's Arch. Pharmacol. 277, 175–190 (1973)Google Scholar
- Powis, G.: The accumulation and metabolism of (±)-noradrenaline by cells in culture. Brit. J. Pharmacol. 47, 568–575 (1973)Google Scholar
- Salt, P. J.: Inhibition of noradrenaline uptake2 in the isolated rat heart by steroids, clonidine and methoxylated phenylethylamines. Europ. J. Pharmacol. 20, 329–340 (1972)Google Scholar
- Trendelenburg, U., Höhn, D., Graefe, K. H., Pluchino, S.: The influence of block of catechol-O-methyl transferase on the sensitivity of isolated organs to catecholamines. Naunyn-Schmiedebergs Arch. Pharmak. 271, 59–92 (1971)Google Scholar
- Uhlig, W., Bönisch, H., Trendelenburg, U.: The O-methylation of extraneuronally stored isoprenaline in the perfused heart. Naunyn-Schmiedeberg's Arch. Pharmacol. 283, 245–261 (1974)Google Scholar
- Wilkinson, G. N.: Statistical estimations in enzyme kinetics. Biochem. J. 80, 324–332 (1961)Google Scholar