THE REQUIREMENT OF SYMPATHETIC INNERVATION FOR THE ACTIVE TRANSPORT OF NOREPINEPHRINE BY THE HEART

¹ Department of Pharmacology, College of Medical Sciences, University of Minnesota, Minneapolis, Minnesota

The uptake in vitro of tritium-labeled norepinephrine (H³-NE) by the heart of the embryonic chick has been studied prior and subsequent to its innervation by the sympathetic nervous system. The innervated heart (5-day-old and older) accumulated H⁵-NE against an external concentration gradient. Noninnervated hearts did not concentrate the catecholamine. Preheating the cardiac tissue, reduction of temperature, reserpine, cocaine and ouabain all markedly inhibited the uptake of H³-NE by innervated hearts but had no effect on the amounts of the amine gaining access to noninnervated hearts. Certain metabolic inhibitors (iodoacetate, fluoride, p-hydroxymercuribenzoate and 2,4-dinitrophenol) similarly blocked the accumulation of H³-NE by innervated but not by noninnervated hearts. Reserpine, cocaine and ouabain more effectively blocked H³-NE uptake by innervated hearts at low than at high external amine concentrations. These data are interpreted to indicate the existence of an active component for the uptake of norepinephrine by the sympathetically innervated embryonic heart which is not present in the noninnervated organ.