Pharmacology of the sympathetic nervous system

Abstract

Drugs may interfere with the efferent sympathetic system, mainly at four different levels: 1) the sympathetic centres (and these in turn are located at different levels), 2) the sympathetic ganglia, 3) the postganglionic sympathetic nerve-endings, and 4) the effector cells (smooth muscle, heart, glands, etc.). In general their actions are brought about by interference with neurohumoral transmission mechanisms — at least peripherally, but probably also centrally. In the periphery, essentially two transmitters are in volved, namely noradrenaline (N.A.) in the postganglionic fibres, and acetylcholine in the preganglionic fibres. However, some postganglionic sympathetic fibres are cholinergic. Some of them have a vasodilator function, but there are certain reasons to doubt that they are of any great importance in primates (Uvnäs, 1964). To complicate the matter further, N.A.-containing fibres have been found, with the aid of the new histochemical fluorescence method of visualising N.A. and related compounds developed by the late N.-Å. Hillarp and his co-workers, to terminate in sympathetic ganglia (Hamberger et al., 1963, 1965), and in parasympathetic ganglia, too, for that matter (Norberg, 1964; Hamberger and Norberg, 1965). The origin and function of these nerve-terminals in the sympathetic ganglia are unknown, but they are probably derived from cell bodies located in the same ganglia, and there is some evidence that they have an inhibitory function.