Receptor - Theories of Receptor ||Pharma Easy Notes || @Pharmacy

Theories of Receptor

Most Therapeutically useful drugs bind only transiently of their intended receptor
O (i) Occupation theory
R (ii) Rate theory
T (iii) The induced-fit theory of enzyme-substrate
M (iv) Macromolecular perturbation theory
A (v) Activation - Aggregation theory

1. Occupation theory

  • Proposed by Gaddum and Clark states
  • The intensity of the pharmacological effect is directly proportional to the number of receptors occupied by the drug.
  • The Pharmacological response of a drug molecule is a
  • Function of dose
  • Number of receptors available &
  • Its intrinsic activity

The rate of combination drug and receptor can be therefore expressed as
K1 [R] [A]
K= Association constant
R= Concentration of the receptor not occupied by the drug
A = Concentration of drug molecule or dose

Similarly, the rate of dissolution of the drug-receptor complex is given by the expression
K2 [RA]
K2 = Dissociation constant
[RA]= Concentration of receptor occupied by the drug

The term [RA]/r = fraction of the total number of receptors occupied by the drug

Relative response = [RA]x/[r] = x/1+KA/[A] -------------------- 1

The response is directly proportional to the intrinsic activity x

2. Rate theory

  • Patan and Rang in 1965 proposed that the most important factor determining drug action is the rate at which drug-receptor combination takes place.
  • The Pharmacological activity is a function of the rate of association and dissociation of the drug with the receptor and not the number of occupied receptors.
  • When the response is proportional to the no. of receptors occupied equation 1 is important and when the response is proportional to the rate of receptor occupation rather than to the proportion of receptor occupied equation 2 of rate theory is important.

3. The Induced -fit theory of enzyme-substrate interaction
  • This theory of Koshland was originally proposed for the action of substrates and enzymes. The drug approaches the receptor a conformation change occurs in the receptor to allow for effective binding.
  • e.g. Acetylcholine may interact with the regulating protein and alters the normal force, which stabilizes the structure of a protein, thereby producing a transient rearrangement in the membrane structure and consequent change in its ion-regulating property.
  • The receptor was suggested to be elastic and it could return to its original confirmation after the drug was released.
  • The drug may also undergo conformational changes.

4. Macromolecular peturbation theory

  • Combining the induced fit and rate theories yield the macromolecular peturbation theory.
  • This theory suggests that two types of confirmation changes exist and that the rate of their existence determines the observed biological response.
  • Agonist produce the specific perturbation required for a biological response while
  • Antagonist produces a non-specific peturbation that fails to yield a biological response.
  • This theory can partially account for the activity of partial agonists.

5. Activation- Aggregation theory

  • It was proposed by changeux and karlion.
  • According to this theory, even in the absence of a drug the receptors are in dynamic equilibrium between the active form (RO), which is responsible for biological and inactive form (TO).
  • Agonist shifts the equilibrium to an active form and antagonist shift to an inactive form.
  • This theory can account for the activity of inverse agonist which neither a typical agonist nor an antagonist but rather produce a response opposite to those of the agonist.

Purpose of this blog- To provide accurate and easy pharma notes ( D. pharm, B. Pharm, M, Pharm. Pharm D) that make your pharmacy study easy. our team covers each and every topic in easy form. For any query plz DM to us.

Comments

Post a Comment

Popular posts from this blog

Receptor - Receptor Families || Pharma Easy Notes || @Pharmacy

Image
Classification All membrane-bound receptors belong to one of the three following systems families based on their structure and function. ( LGKI ) L igand-gated ion channels G - Protein-coupled receptor K inase-linked receptors I ntracellular receptors 1. Ligand-gated ion channels Ion channels are protein complexes that traverse the cell membrane and form a tunnel through it. The function of an ion channel is - to allow the flow of ions across the cell membrane and there are specific ion channels for sodium, Potassium, Calcium, and chloride ions. Without ion tunnels, ions could not cross the fatty cell since many enzyme-catalyzed reactions are dependent on ionic concentration. In the resting state, the ion channel is closed and the receptor's binding site is unoccupied . The signal to open the ion channel comes from the chemical messenger which binds to the receptors and causes it to change shape which travels through the entire ion channel. The proteins making up the ion channe
Read more

Schedule 'V' and schedule 'W' || Pharmaeasynotes ||@Pharmacy || Jurispru...

Image
Schedule 'V' Standards for patent or proprietary medicines. These standards for patent or proprietary medicines shall be those laid down in Schedule V and such medicines shall also comply with the standards laid down in the Second Schedule to the Act. Schedule 'W' List of drugs marketed under generic names. Its label contains the Names and quantities of active ingredients. If vitamins are present, the following words must be written "For therapeutic use" "For prophylactic use" "For pediatric use " and age of child /infant. 
Read more

B. Pharm syllabus || According to PCI || BP 102T||BP 108 P ||Frist semester

Image
BP102T. PHARMACEUTICAL ANALYSIS (Theory)  45 Hours Scope:  This course deals with the fundamentals of analytical chemistry and principles of electrochemical analysis of drugs  Objectives:  Upon completion of the course, a student shall be able to   understand the principles of volumetric and electrochemical analysis   carryout various volumetric and electrochemical titrations   develop analytical skills  Course Content:   UNIT-I                                                                                       10 Hours  (a) Pharmaceutical analysis - Definition and scope  i) Different techniques of analysis  Ii) Methods of expressing concentration iii) Primary and secondary standards.  iv) Preparation and standardization of various molar and normal solutions- Oxalic acid, sodium hydroxide, hydrochloric acid, sodium thiosulphate, sulphuric acid, potassium permanganate and ceric ammonium sulfate.  (b)Errors:  Sources of errors, types of errors, methods of minimizing errors, accuracy
Read more