Parasympathomimetic action

This matter is given some consideration in Chapter m. In passing we may note here that it is because of the parasympathomimetic action of D.F.P. and related compounds that the term nerve gas has been applied. 

Early studies of the parasympathetic nervous system showed that the alkaloid muscarine mimicked the effects of parasympathetic nerve discharge that is, the effects were parasympathomimetic. Application of muscarine to ganglia and to autonomic effector tissues (smooth muscle, heart, exocrine glands) showed that the parasympathomimetic action... 

Pathophysiology can influence muscarinic activity in other ways as well. Circulating autoantibodies against the second extracellular loop of cardiac M2 muscarinic receptors have been detected in some patients with idiopathic dilated cardiomyopathy and those afflicted with Chagas1 disease caused by the protozoan Trypanosoma cruzi. These antibodies exert parasympathomimetic actions on the heart that are prevented by atropine. In animals immunized with a peptide from the second extracellular loop of the M2 receptor, the antibody is an allosteric modulator of the receptor. Although their role in the pathology of heart failure is unknown, these antibodies should provide clues to the molecular basis of receptor activation because their site of action differs from the orthosteric site where acetylcholine binds (see Chapter 2). 

NEUROTOXIN constituent of the fly agaric fungus Amanita muscaria and various /nocyfte spp. It is a very potent MUSCARINIC CHOLINOCEPTOR AGONIST with pronounced PARASYMPATHOMIMETIC actions. It is a HYPOTENSIVE, causes bronchoconstriction and stimulates gut, bladder and exocrine glands. Stereoisomers show only a fraction of the activity, and it is valuable as a pharmacological tool in studies on muscarinic receptors. It is very toxic orally, with stimulatory actions on the CNS (atropine sulphate may be used as an antidote). 

The physiological effects of LSD are related to its sympathomimetic actions and include mydriasis (most frequent and consistent), tachycardia, increased body temperature, diaphoresis, and hypertension at higher doses, parasympathomimetic actions may be observed (e.g., salivation, lacrimation, nausea, and vomiting [muscarinic actions]). Neuromuscular effects may include paresthesia, muscle twitches, and incoordination (nicotinic actions)... 

Reserpine possesses one outstanding pharmacological property it releases the monoamines from both their central and peripheral storage sites. The other noteworthy property of reserpine is its parasympathomimetic action which leads to hypotension, bradycardia, miosis and hypothermia. ... 

Muscarinic agonists mimic the muscarinic effects of ACh and typically are longer-acting congeners of ACh or natural alkaloids that display httle selectivity for the various subtypes of muscarinic receptors. The muscarinic, or parasympathomimetic, actions of the drugs considered in this chapter are practically equivalent to the effects of postganglionic parasympathetic nerve impulses hsted in Table 6-1. AH of the actions of ACh and its congeners at muscarinic receptors can be blocked by atropine. 

Atrial fibrillation In atrial flutter and fibrillation, it is desirable to reduce the conduction velocity or increase the refractory period of the atrioventricular node so that ventricular rate is decreased. The parasympathomimetic action of digitalis effectively accomplishes this therapeutic objective. 

Digitalis increases the AV node refractory period—a parasympathomimetic action. Its effects on the ventricles include shortened action potential and QT interval, and a change in repolarization with inversion of the T wave. The answer is (B). 

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