Adrenergic Drugs

Adrenergic Drugs

INTRODUCTION

Sympathetic nervous system is an important regulator of the activities of the vital organs, such as heart and peripheral vasculature, especially in response to stress. The effect of sympathetic stimulation is mediated by the release of norepinephrine from the nerve terminals that serve to activate the adrenoreceptors on postsynaptic sites. Also, in response to a variety of stimuli, such as stress, the adrenal medulla releases epinephrine, and it is transported in the blood to the target tissues. Drugs that mimic the action of sympathetic system are called sympathomimetic drugs. Like cholinomimetic drugs, the sympathomimetics can be grouped by their mode of action and by the spectrum of receptors. Some of the drugs (e.g. epinephrine, norepinephrine) act by a direct mode, that is, they interact with and activate adrenoceptor. Others act indirectly; their actions are dependent on the release of endogenous catecholamine. These indirect agents may have either of the different mechanisms:

1. Displacement of stored catecholamine from adrenergic nerve ending (e.g. amphetamine and tyramine).

2. By inhibition of reuptake of catecholamine already released (e.g. cocaine and tricyclic antidepressants).

3. Some drugs have both direct and indirect action.