Principles of drug action

1 Principles of drug action





Questions



image How can a drug be defined?

image What are the types of receptor?

Under normal physiological conditions, hormones (e.g. epinephrine) or neurotransmitters (e.g. acetylcholine) play an important role in transmitting information from one cell to another. They do so by binding to and inducing an alteration in the conformational state (structure) of specific proteins (receptors).



Drugs


Drugs are chemicals that alter the biological response of cells. Their chemical structure often mimics a natural substance in the body but they can be chemically distinct; in either case they selectively target receptors (Fig. 3.1.1). The binding of a drug to its receptor is the first step in a series of complex reactions inside the cell that ultimately evokes a therapeutic effect and, therefore, provides a ‘magic bullet’ for the treatment of disease. The drug can either initiate an endogenous process or inhibit the action of endogenous hormones and neurotransmitters.


image

Fig. 3.1.1 Structure of adrenoceptor ligands.



Receptors


There are many different types of receptor found on the surface or inside cells. Receptors within cells can be situated either in the cytoplasm or in the nucleus, bound to regions of DNA (response elements) near genes whose activity is to be regulated.




G-protein-coupled receptors


This large protein family comprises cell surface receptors (e.g. β-adrenoceptor, muscarinic receptor) that are activated by hormones and neurotransmitters. A characteristic feature of these receptors is that they contain seven membrane-spanning domains and their activation leads to the subsequent synthesis of intracellular second messengers, which activate numerous proteins within cells as an amplification cascade (Fig. 3.1.2).


image

Fig. 3.1.2 G-protein-coupled receptors. (A) Linkage occurs to targets via specific subunits; (B) activation of adenylyl cyclase; (C) activation of phospholipase C. PIP2, phosphatidylinositol 4,5-bisphosphate; IP3, inositol 1,4,5-trisphosphate; DAG, diacylglycerol.

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Jul 18, 2016 | Posted by in PHARMACY | Comments Off on Principles of drug action

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