Drugs and receptors

The free energy AG can also be related to the equilibrium constant K between the free and the bound state of drug and receptor ... 

A basic understanding of the interaction between drugs and receptors underlies much of what is covered in the examinations. 

After binding of drug and receptor, a cascade of signal transductions occur within the cell and are manifested as a variety of effects on the diseased biochemical pathways. 

Fig. 2.8 Schematic illustrating equilibrium between drug and receptor.

Competition for receptors, hence receptor antagonism, is governed by the law of mass action that is, the interaction between drug and receptor depends on the concentration of drug in the vicinity of the receptor and the number of receptors present. Because agonist and antagonist have an affinity for the same receptors, the two substances compete for binding to the receptors. 

Most users agree Salvia divinorum is quite unique, and some find its effects unsettling. Its active principle, salvinorin A, is structurally unique among psychoactive drugs, and receptor binding studies have revealed nothing, which could indicate a previously unknown pathway in the brain. 

The concept of a lock and key relationship between drug and receptor is based on work done by which of the following ... 

Mathematically, the interaction between drug and receptor can be represented by the following basic relationship ... 

The most interesting case arises by removing assumption HI, i.e., when the reaction between drug and receptor is not at equilibrium [428]. This happens when relatively slow rates of association and dissociation of the complex are observed. Under these conditions, a slow dynamic receptor-binding model is most applicable. By maintaining the proportionality between the effect and the concentration of the drug-receptor complex, (10.4) can be written in terms of the effect... 

In the pharmacodynamic model, the drug concentration at the receptor site is proportional to the drug concentration in the plasma, regardless of the pharmacokinetic model (one compartment or multicompartment), and the interaction between the drug and receptor is directly and rapidly reversible after drug administration. 

QSAR theories are convenient for the design of new analogs of a known active compound but these theories are not always able to go beyond the chemical frame of the particular family studied. Considering structure-activity studies in the light of the three dimensional specificity of molecular interactions between drugs and receptors, conformational properties appear to be essential. 

In order for a drug to interact with an enzyme or a receptor, it has to approach, then bind to a binding site. The bulk, size, and shape of the drug may have an influence on this process. For example, a bulky substituent may act like a shield and hinder the ideal interaction between drug and receptor. Alternatively, a bulky substituent may help to orientate a drug properly for maximum receptor binding and increase activity. 

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