PHARMACOLOGICAL PROPERTIES OF UNKNOWN DRUG

Pharmacological Properties of Unknown Drug

Pharmacological Properties Of Unknown Drug

Objective

The overall objective of the experiments was to investigate our unknown agonist to find its susceptibility to two different antagonists; Atropine and Chlorphenamine and using this to identify the receptor selectivity of our sample.

Introduction

A drug is a substance that affects the biological functions of cells and tissues. Pharmacology is the study of the effects that drugs have on the function of host tissues. Drugs elicit an effect through interactions with receptors (protein macromolecules found in or on cells) in the body. Receptors are recognition sites that mediate the actions of endogenous chemical messengers. However, if a drug molecule possesses a similar conformation with an endogenous chemical messenger, it may be recognized by the receptor specific for that particular chemical messenger. As there are different types of receptors in the body, different biochemical and physiological effects specific to the activation or blockade of each receptor type will result depending on the selectivity of drugs administered. Selectivity of a drug depends on its affinity for a certain receptor type and once bound to the receptor will elicit a biological response (efficacy). A drug that occupies a receptor and thereafter affects it such that a biological response occurs is called an agonist. A drug that occupies a receptor but does not induce a biological response is called an antagonist. A competitive antagonist is one that occupies a receptor but its binding can be reversed. The binding of a non-competitive antagonist to a receptor is irreversible. The effect an agonist and antagonist have can be quantitatively studied by means of a log dose-response (concentration-effect) curve graph. An estimation of the maximal biological response (Emax) a drug can produce and the concentration of drug required to produce half the maximum biological response (ED50) can be made from log dose-response curves.



Figure 1: Dose response curve showing the maximum efficacy (Emax) and the Potency (ED50)

Emax and ED50 are useful in the investigation of the pharmacological properties of a drug and comparisons of potencies can be made when log dose-response curves of several different drugs are plotted. Similarly, the effect an antagonist has on an agonist can be seen in a log dose-response curve. A competitive antagonist makes an agonist look less potent, while a non-competitive antagonist reduces the maximum response (efficacy) that an agonist can produce.

Figure 2: Dose response curve showing the effects of competitive antagonism of the agonist with respect to Emax and ED50

Figure 3: Dose response curve showing the effects of non-competitive antagonism of the agonist with respect to Emax and ED50

The autonomic nervous system (ANS) consists of two major divisions: sympathetic nervous system and parasympathetic nervous system. The actions of the two systems are often in opposite directions (e.g. contraction of gastrointestinal smooth muscle by parasympathetic action and relaxation of gastrointestinal smooth muscle by sympathetic action), but in some tissues the action of one system is unopposed (e.g. the contraction of ciliary muscle in the eye by parasympathetic ...