Parasympatholytic effects

Kuhnen-Clausen, D. Investigations on the parasympatholytic effect of toxogonin on the guinea-pig isolated ileum. Eur. J. Pharmacol. 9 85-92, 1970. 

Lindgren, P., Sundwall, A. 1960. Parasympatholytic effects of TMB-4 [1,1 -trimethylene bis (4-formylpyrldlnlum bromide)-dioxlme] and some related oximes in the cat. Acta Pharmacol. Toxicol. 17 69-83. 

Naturally occurring tropane alkaloids and semisynthetic derivatives are used as spasmolytics because of their anticholinergic (-parasympatholytic) effect through competitive inhibition of acetylcholine at receptors in smooth muscles. 

Biperiden, a substance with a parasympatholytic effect, is used in the treatment of Parkinson s disease. It is available on prescription only, the therapeutic dose being 2-12 mg/day. Apart from this use, biperiden is also prescribed for the treatment of extrapyramidal motor disturbances caused by the use of highly active neuroleptic drugs (haloperidol, benperidol etc.). The consumption of 20-30 mg biperiden produces a euphoric effect which can occasionally culminate in a reversible psychosis. 

Parasympatholytic effects are caused by agents that block the action of acetykhoBne... 

Parasympatholytics have a wide therapeutic margin Rarely life-threatening, poisoning with atropine is characterized by the following peripheral and central effects ... 

Rhinitis. Nasal discharge could be prevented by parasympatholytics however, other atropine-like effects (pp. 

Motion sickness. Effective prophylaxis can be achieved with the parasympatholytic scopolamine (p. 106) and H antihistamines (p. 114) of the diphenyl-methane type (e.g., diphenhydramine, meclizine). Antiemetic activity is not a property shared by all parasympatho-lytics or antihistamines. The efficacy of the drugs mentioned depends on the actual situation of the in vidual (gastric filling, ethanol consumption), environ-... 

Pharmacology Trospium is an antispasmodic, antimuscarinic agent. Trospium antagonizes the effect of acetylcholine on muscarinic receptors in cholinergically innervated organs. Its parasympatholytic action reduces the tonus of smooth muscle in the bladder. Trospium increases maximum cystometric bladder capacity and volume at first detrusor contraction. 

Pharmacology Ipratropium for oral inhalation is an anticholinergic (parasympatholytic) agent that appears to inhibit vagally mediated reflexes by antagonizing the action of acetylcholine. The bronchodilation following inhalation is primarily a local, site-specific effect, not a systemic one. 

Atropine, an alkaloid from Atropa belladonna, is the classical parasympatholytic compound. It competes with acetylcholine for the binding at the muscarinic receptor. Its affinity towards nicotinic receptors is very low, so that it does not interfere with the ganglionic transmission or the neuromotor transmission, at least in therapeutic dosages. However, in the central nervous system muscarinic receptor do play an important role and while atropine can penetrate the blood-brain barrier it exerts pronounced central effects. Atropine, like all other antagonists of the muscarinic acetylcholine receptor inhibit the stimulatory influence of the parasympathetic branch of the autonomous nervous system. All excretory glands (tear, sweat, salivary, gasto-intestinal, bronchi) are... 

All smooth muscle activity which is physiologically under a strong parasympathetic influence is effectively inhibited by atropine, for example in the gastrointestinal, genitourinary and respiratory tract. Parasympatholytics are very useful drugs in the treatment of spastic conditions (colic) in these regions. 

Muscarinic antagonists are sometimes called parasympatholytic because they block the effects of parasympathetic autonomic discharge. However, they do not "lyse" parasympathetic nerves, and they have some effects that are not predictable from block of the parasympathetic nervous system. For these reasons, the term "antimuscarinic" is preferable. 

Most TA referred herein (e.g. hyoscyamine, scopolamine, N-buty 1-scopolamine, Fig. 1) primarily act as competitive antagonists of acetylcholine (anticholinergics) in the synaptic cleft (parasympatholytic) [29, 35], Thus therapeutic effects may include mydriasis, spasmolysis of the respiratory system, GIT and overactive bladder, anaesthesia and analgesia [33],... 

Homatropine is a synthetic parasympatholytic representing the ester of tropine and mandelic add (Fig. 1). This drug antagonizes acetylcholine on MR and is thus used as mydriatic with less detrimental paralytic effects on ciliary eye muscle than atropine but showing faster and shorter action [1,33], Therefore, it belongs to the WHO list of essential medicines as mydriatic eye drops representing an alternative to atropine [41],... 

From the influence of the autonomic nervous system it follows that all sympatholytic or sympathomimetic and parasympatholytic or parasympathomimetic drugs can produce corresponding effects on cardiac performance. These possibilities are exploited therapeutically for instance, p-blockers for suppressing excessive sympathetic drive (p. 96) ipratropium for treating sinus bradycardia (p. 108). An unwanted activation of the sympathetic system can result from anxiety, pain, and other emotional stress. In these cases, the heart can be protected from harmful stimulation by psychopharmaceuticals such as benzodiazepines (diazepam and others important in myocardial infarction). 

Pilocarpine is a widely studied peripheral stimulant of the parasympathetic system (101). It is used topically as a myotic to counteract the mydriatic effect of atropine and other parasympatholytic drugs. It has clinical value in the treatment of glaucoma when used as eye drop solutions ranging from 0.5 to 10% in concentration (102). Pilocarpine is reported to stimulate the growth of hair and therefore was employed in hair lotions (1). Internally, it was used as a diaphoretic in the treatment of nephritis (103). 

Figure 8-2 Mydriasis induced by 2.5% and 10% phenylephrine (w = 112 eyes). (Reprinted with permission from Paggiarino DA, Brancato LJ, Newton RE. The effect on pupil size and accommodation of sympathetic and parasympatholytic agents. Ann Ophthalmol 1993 25 244-253.)...

Paggiarino DA, Brancato LJ, Newton RE. The effect on pupil size and accommodation of sympathetic and parasympatholytic agents.Ann Ophthalmol 1993 25 244-253. 

These three general effects of parasympatholytics can be expected in some degree from any of the known drugs, though occasionally one must administer rather heroic doses to demonstrate the effect. The mydriatic and cyclopicgic... 

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