Autonomic Pharmacology

The human nervous system can be divided into two major functional areas the somatic nervous system and the autonomic nervous system (ANS). The somatic division is concerned primarily with voluntary function—that is, control of the skeletal musculature. The ANS is responsible for controlling bodily functions that are largely involuntary, or automatic, in nature. For instance, the control of blood pressure (BP) and other aspects of cardiovascular function is under the influence of the ANS. Other involuntary, or vegetative, functions such as digestion, elimination, and thermoregulation are also controlled by this system. 

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Katzung, B.G., Introduction to autonomic pharmacology, in Basic and Clinical Pharmacology, 8th ed., Katzung, B.G., Ed., Lange Medical Books/ McGraw-Hill, New York, 2001, chap. 6. 

AccessMedicine Print Chapter 6. Introduction to Autonomic Pharmacology... 

Katzung BG. Introduction to autonomic pharmacology. In Katzung BG, ed. Basic and Clinical Pharmacology. 9th ed. New York Lange Medical Books/McGraw Hill 2004. 

Choline esters are poorly absorbed and poorly distributed into the central nervous system because they are hydrophilic. Although all are hydrolyzed in the gastrointestinal tract (and less active by the oral route), they differ markedly in their susceptibility to hydrolysis by cholinesterase in the body. Acetylcholine is very rapidly hydrolyzed (see Chapter 6 Introduction to Autonomic Pharmacology) large amounts must be infused intravenously to achieve concentrations high enough to produce detectable effects. A large intravenous bolus injection has a brief effect, typically... 

The primary cardiovascular effects of muscarinic agonists are reduction in peripheral vascular resistance and changes in heart rate. The direct effects listed in Table 7-3 are modified by important homeostatic reflexes, as described in Chapter 6 Introduction to Autonomic Pharmacology and depicted in Figure 6-7. Intravenous infusions of minimal effective doses of acetylcholine in humans (eg, 20-50. g/min) cause vasodilation, resulting in a reduction in blood pressure, often accompanied by a reflex increase in heart rate. Larger doses of acetylcholine produce bradycardia and decrease atrioventricular node conduction velocity in addition to the hypotensive effect. 

As suggested in Chapter 6 Introduction to Autonomic Pharmacology, the Mi receptor subtype appears to be located on central nervous system neurons, sympathetic postganglionic cell bodies, and many presynaptic sites. M2 receptors are located in the myocardium, smooth muscle organs, and some neuronal sites. M3 receptors are most common on effector cell membranes, especially glandular and smooth muscle cells. 

Blood vessels receive no direct innervation from the parasympathetic nervous system. However, parasympathetic nerve stimulation dilates coronary arteries, and sympathetic cholinergic nerves cause vasodilation in the skeletal muscle vascular bed (see Chapter 6 Introduction to Autonomic Pharmacology). Atropine can block this vasodilation. Furthermore, almost all vessels contain endothelial muscarinic receptors that mediate vasodilation (see Chapter 7 Cholinoceptor-Activating Cholinesterase-Inhibiting Drugs). These receptors are readily blocked by antimuscarinic drugs. 

Chapter 6 Introduction to Autonomic Pharmacology). The -receptor-mediated response is probably of greater pharmacologic significance than the B-stimulant response. Alpha2 receptors may also decrease salt and water flux into the lumen of the intestine. 

Cocaine is a local anesthetic with a peripheral sympathomimetic action that results from inhibition of transmitter reuptake at noradrenergic synapses (see Chapter 6 Introduction to Autonomic Pharmacology). It readily enters the central nervous system and produces an amphetamine-like effect that is shorter lasting and more intense. The major action of cocaine in the central nervous system is to inhibit dopamine reuptake into neurons in the "pleasure centers" of the brain. These properties and the fact that it can be smoked, "snorted" into the nose, or injected for rapid onset of... 

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