Chapter 8 - Drugs affecting the sympathetic system

Abstract

This chapter focuses on drugs affecting the sympathetic system. In the parasympathetic branch of the autonomic nervous system, acetylcholine is the transmitter released from both preganglionic and postganglionic nerve terminals although the actions of acetylcholine are different at the postsynaptic and postjunctional receptors. However, in the sympathetic branch, although acetylcholine is the transmitter in the ganglia, the catecholamine noradrenaline is released from the majority of postganglionic nerve terminals. Noradrenaline, like adrenaline, is a catecholamine. Noradrenaline is synthesized from the amino acid precursor, l -tyrosine, which is a constituent of diet. The lack of specificity of the enzymes involved in the synthesis of catecholamines results in the existence of other possible pathways in which a number of related substances are formed. The synthesis of adrenaline in the chromaffin cells is also controlled by the secretion of glucocorticoids from the adrenal cortex. The noradrenaline that is synthesized in postganglionic sympathetic nerve terminals is stored in vesicles that are similar in size to those present in cholinergic nerve terminals but that can be distinguished by their different staining characteristics when they are examined histochemically and by their density in the electron microscope.