The Inhibition of Noradrenaline Uptake by Sympathomimetic Amines in the Rat Isolated Heart

In the rat isolated heart, noradrenaline can be accumulated by two distinct processes. The first process (Uptake1) is half saturated at a ()-noradrenaline concentration of 0.11 pg/ml. and continues to operate at external noradrenaline concentrations up to 1 ,ug/ml. (Iversen, 1963). The second process comes into play at slightly higher concentrations and becomes half saturated at 42.6 ,ug/ml. (Iversen, 1965b). Both of these processes act also upon adrenaline, which competes for uptake when noradrenaline is also present (Iversen, 1965a, b). It seems probable, therefore, that other sympathomimetic amines would have an affinity for the systems operative in accumulation, and indeed, there is some evidence in the literature that amphetamine, tyramine and ephedrine inhibit noradrenaline uptake (Dengler, Spiegel & Titus, 1961;