Regulation of catecholamine release: α-Receptor mediated feed-back control in peripheral and central neurones

Abstract

Publisher Summary This chapter describes a study analyzing the regulation of catecholamine release: α-receptor mediated feedback control in peripheral and central neurons. It tested the influence of phentolamine, after both the neuronal and the extra-neuronal binding of noradrenaline (NA) had been blocked by high concentrations of cocaine and (±)-metanephrine which were added immediately after preperfusion with 3 H-noradrenaline. Phentolamine enhanced the stimulation-induced overflow of tritium even in the presence of these drugs and, thus, by a mechanism other than an inhibition of the neuronal or extraneuronal binding of noradrenaline. The results indicate that α-adrenolytic drugs do not enhance the stimulation-induced overflow of noradrenaline by blocking any of the known pathways of its inactivation within the tissue. Per exclusionem it can be inferred that these drugs increase the amount of transmitter secreted per impulse from the nerve terminals. It is also concluded that α-receptors exist in the vicinity to the cardiac adrenergic nerve endings. When these receptors are activated, the release of noradrenaline declines. A local feedback inhibition curtails the secretory response to stimulation.