Acetylcholine drugs blocking

We will conclude this chapter by referring to a term often used for those symptomatic drugs inhibiting the action of the autonomic nervous system by interfering with the effect of the chemical mediators involved. There are two groups. (1) Para-sympatholytic drugs block the action of acetylcholine. These are included within the wider class of spasmolytics which, as the name suggests, check or eliminate spasms. (2) Sympatholytics inhibit the action of adrenaline, noradrenaline and the sympathetic nervous system. 

Thus, the anticholinergic activity of the alkaloid hyoscyamine is almost entirely confined to the (—)-isomer, and the (+)-isomer is almost devoid of activity. The racemic ( )-form, atropine, has approximately half the activity of the laevorotatory enantiomer. An anticholinergic drug blocks the action of the neurotransmitter acetylcholine, and thus occupies the same binding site as acetylcholine. The major interaction with the receptor involves that part of the molecule that mimics acetylcholine, namely the appropriately positioned ester and amine groups. The chiral centre is adjacent to the ester, and also influences binding to the receptor. 

Moreover, their response to different drugs tells us something important about the role that these two different acetylcholine receptors play in the brain and the body. Some drugs block, or antagonize, these receptors, whereas other drugs enhance, or stimulate (i.e., act as agonists of), them. Let s now look at several types of drugs to see what their actions reveal about the function of these receptors. 

It is believed that although antipsychotic medications block norepinephrine, serotonin, and acetylcholine, their primary action is as central dopamine antagonists (Galenberg, 1991 Meyer Quenzer, 2005). That is, these drugs block central dopamine receptors, particularly the Dj subtype, and thus inhibit dopaminergic neurotransmission in the brain. The postsynaptic receptor blockade in the limbic system is thought to reduce the schizophrenic symptoms. 

Anticholinergic. A drug that blocks the effects of the neuro-transmitter, acetylcholine. 

Antagonists of muscarinic acetylcholine receptors had widely been used since 1860 for the treatment of Parkinson s disease, prior to the discovery of l-DOPA. They block receptors that mediate the response to striatal cholinergic interneurons. The antiparkinsonian effects of drugs like benzatropine, trihexyphenidyl and biper-iden are moderate the resting tremor may sometimes respond in a favorable manner. The adverse effects, e.g., constipation, urinary retention, and mental confusion, may be troublesome, especially in the elderly. 

Anticholinergic Drugs that block acetylcholine receptors, although the term is used specifically for antagonists at muscarinic acetylcholine receptors (anti-muscarinics), like atropine and scopolamine. 

Short-term memory tasks increase high-affinity uptake of acetylcholine, whereas long-term reference memory tasks cause an acute increase followed by a long-lasting decrease and inhibition (Decker et al. 1988). In contrast, the drug scopolamine creates amnestic effects by blocking muscarinic receptors and decreasing acetylcholine levels. Thus, at... 

Irreversible anticholinesterases include the organophosphorus inhibitors and ambenonium, which irreversibly phosphorylate the esteratic site. Such drugs have few clinical uses but have been developed as insecticides and nerve gases. Besides blocking the muscarinic receptors with atropine sulphate in an attempt to reduce the toxic effects that result from an accumulation of acetylcholine, the only specific treatment for organopho-sphate poisoning would appear to be the administration of 2-pyridine aldoxime methiodide, which increases the rate of dissociation of the organophosphate from the esteratic site on the enzyme surface. 

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