RESERPINE-INDUCED RELEASE OF NOREPINEPHRINE FROM ISOLATED SPONTANEOUSLY BEATING GUINEA-PIG ATRIA

¹ Department of Pharmacology, Harvard Medical School, Boston, Masachusetts

In a series of experiments on isolated spontaneously beating guinea-pig atria, acutely administered reserpine had dual chronotropic effects. A rate-lowering effect appeared to be exerted directly on the pacemaker, while a rate-increasing effect depended on the release of physiologically significant amounts of norepinephrine. Inhibition of monoamine oxidase simultaneously increased norepinephrine release 5-fold and antagonized norepinephnine depletion. It was calculated that no more than 7% of the depletion in atria from unpretreated animals could have represented escape of free norepinephrine, while 93% or more must have represented degradation by monoamine oxidase.