Scopolamine receptor specificity

An example of the procedure is shown in Figure 6.22. Specifically, a series of Schild analyses were done for the reference antagonist scopolamine in the presence of different concentrations of the test antagonist atropine. The resultant plot according to Equation 6.38 yields an estimate of the KB for atropine as the intercept (Log (k— 1) = 0). If atropine had secondary effects on the system, this procedure will cancel them and allow measurement of the receptor antagonism. An example of this procedure is given in Section 12.2.5. 

Alkaloids are heterocyclic basic compounds and widespread in plants. Many of them have specific targets in organisms. For example, the alkaloids atropine and scopolamine of Belladonna are specific antagonists at muscarinic receptors. 

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

Other drugs are ACh receptor blockers. Specific blocking agents acting on ganglionic nicotinic (N, ) receptors are hexamethonium and mecamylamine. Those acting on the end-plate nicotinic receptors (N, ) are tubocurarine, atracurium, and sucdnylcholine. Those acting on muscarinic (M) receptors include atropine, benztropine, and scopolamine. 

The term anticholinergic as used in the context of this discussion refers more specifically to compounds that selectively block the brain s muscarinic receptor (now known to consist of several sub-types). Atropine (hyoscyamine) and scopolamine (hyoscine) are the most familiar medicinal anticholinergics. Historically, they were obtained from of the botanical family Solanaceae, which includes Jimson (or loco) weed, mandrake root, henbane, belladonna, and nightshade. Atropine and scopolamine are esters of tropic acid and contain a tertiary nitrogen moiety. This gives them the ability to cross the blood-brain barrier and block central muscarinic cholinergic receptors by competitive inhibition with acetylcholine, the natural neurotransmitter at these sites. 

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