Chemical, electron microscopic and physiological observations on the role of catecholamines in the carotid body

Abstract Chemical determinations revealed large amounts of dopamine, noradrenaline and adrenaline, in the carotid body of the cat. The cathecholamine (CA) content of normally innervated and chronically synmpathectomized carotid bodies was essentially the same. It did not change by vigorous and prolonged carotid body stimulation either in situ or in vitro . High doses of reserpine reduced appreciably the noradrenaline content of the carotid body; the contents of dopamine and adrenaline also were reduced but to a lesser degree. Electron microscopy shoed the presence of numerous dense-cored vesicles in the glomus cells of the carotid body; these vesicles occurred only rarely in the capsular cells and in the carotid nerve terminals. No detectable change in the vesicular content, appearance or distribution was induced by prolonge dhypoxia, reserpinization, adrenalectomy or chronic section of the carotid nerve or sympathetic supply. Acute and chronic reserpinization of cats did not change the sensitivity and reactivity of carotid bodies (either in situ or in vitro to ACh, anoxic or asphyxic stimulation. In vitro , high doses of adrenaline, noradrenaline, dopamine, dl -DOPA and tyramine failed to produced chemoreceptor excitation or marked depression of the chemosensory discharges. The lack of effect of CA on chemoreceptor activity was not changed by reserpinization or inactivation of monaminoxidase with nialamide. Prolonged superfusion with dischloroisoproterenol, a β-adrenergic blocking agent, reduced chemoreceptor discharges by inducing nerve block. It is concluded that CA contained in the carotid body do not play a significant role in the generation of the chemosensory discharges.