Autonomic drug

The drugs which act on the autonomic nervous system (ANS) and control the vital internal processes which ordinarily, are not under volition, are known as autonomic drugs. 

Noradrenaline is released particularly at the target organs and ultimately gives rise to the ensuing contraction of the cardiac muscles and ultimately an enhancement in the heart rate. Besides, it is also helpful in relaxing the smooth muscles and thereby causes a visible reduction in the contractions of the Gl-tract as well as the urinary tract. It also minimises a distinct reduction in salivation and lowers dilatation of the peripheral blood vessels particularly. 

however, pertinent to mention here that the effects of autonomic (sympathetic) nervous system activation and, therefore, the effects of sympathomimetic drugs are evaluated mostly by the specific type and ultimately the localization of the post synaptic receptor to which the released neurotransmitter or exogenous sympathomimetic binds finally. 

The autonomic drugs may be elassified into the following eategories, namely  

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By using drugs that mimic or block the actions of chemical transmitters, we can selectively modify many autonomic functions. These functions involve a variety of effector tissues, including cardiac muscle, smooth muscle, vascular endothelium, exocrine glands, and presynaptic nerve terminals. Autonomic drugs are useful in many clinical conditions. However, a very large number of drugs used for other purposes have unwanted effects on autonomic function. 

Autonomic function is integrated and regulated at many levels, from the CNS to the effector cells. Most regulation uses negative feedback, but several other mechanisms have been identified. Negative feedback is particularly important in the responses of the ANS to the administration of autonomic drugs. 

Table 6-3 Direct Effects of Autonomic Nerve Activity on Some Organ Systems. Autonomic Drug Effects Are Similar But Not Identical (See Text). ...

Consequently, the many side effects and beneficial effects of autonomic drugs can be attributed to the interaction of various agents with different receptors. The significance of autonomic receptor subtypes as well as the use of specific cholinergic and adrenergic drugs in treating various problems are covered in more detail in Chapters 19 and 20. 

Atropine, hyoscyamine, and hyoscine are cholinergic receptor blocking agents. Autonomic drugs have extensive clinical applications. They have the following uses ... 

FIGURE 14.6 Miosis and mydriasis caused by autonomic drugs. N = nerve. 

A basic understanding of the interactions of autonomic nerves with each other and with their effector organs is essential for an appreciation of the actions of autonomic drugs, especially because of the significant reflex (compensatory) effects that may be evoked by these agents. 

Because the effector cell receptors (muscarinic, <, and 6) are not blocked, patients receiving ganglion-blocking drugs are fully responsive to autonomic drugs acting on these receptors. In fact, responses may be exaggerated or even reversed (eg, norepinephrine may cause tachycardia rather than bradycardia), because homeostatic reflexes, which normally moderate autonomic responses, are absent. 

Katzung PHARMACOLOGY, 9e > Section II. Autonomic Drugs > Chapter 9. Adrenoceptor-Activating Other Sympathomimetic Drugs > ... 

Other classes of drugs not included in Figure 22-3 that may exert sedative effects include most antipsychotic and many antidepressant drugs and certain antihistaminic agents (eg, hydroxyzine, promethazine). As discussed in other chapters, these agents differ from conventional sedative-hypnotics in both their effects and their major therapeutic uses. Since they commonly exert marked effects on the peripheral autonomic nervous system, they are sometimes referred to as "sedative-autonomic" drugs. Certain antihistaminics with sedative effects are available in over-the-counter sleep aids. Their autonomic properties and their long durations of action can result in adverse effects. 

Phenobarbital, meprobamate, and sedative-autonomic drugs are used occasionally as antianxiety agents. The antihistaminics (diphenhydramine, hydroxyzine, promethazine) continue to be used presurgically for their sedative and muscarinic receptor blocking actions. 

Shaffer RN. Problems in the use of autonomic drugs in ophthalmology. In Leopold IH, ed. Ocular therapy complications and management. St. Louis CV Mosby, 1967 2 18-23. 

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