What is Receptor?

What is Receptor


It is a specific drug binding site in a cell or on its surface that mediates the action of drug.

When a drug is introduced into the body, it binds to its specific receptor and produces a biochemical response, which can either stimulate or inhibit the receptor’s normal activity.

Drug receptors are typically found on the surface of cells or within the cell, and they are highly specific to certain drugs or classes of drugs. The interaction between a drug and its receptor is often the key determinant of the drug’s therapeutic effect, as well as its side effects.

Examples of drug receptors include opioid receptors, which are targeted by drugs like morphine to produce pain relief, and beta-adrenergic receptors, which are targeted by drugs like albuterol to open up airways in the lungs. Understanding the molecular structure and function of drug receptors is a crucial aspect of drug development and can lead to the discovery of new therapies for a wide range of medical conditions.

Nature of drug receptors:

Drug receptors maybe:

  1. Regulatory proteins that mediate actions of neurotransmitters, autacoids and hormones.
  2. Enzymes which may be inhibited (or less commonly, activated) by binding a drug for example dihydrofolate reductase, the receptor for antineoplastic drug methotrexate.
  3. Structural protein such as tubulin, the receptor for colchicine (an anti-inflammatory agent).
  4. Transport protein such as NA+ , K+ -ATPase (the membrane receptor for cardioactive digitalis glycosides).

Some drugs such as mannitol do not have specific receptors.

Regulation of receptors

Down regulation of receptors:

In down regulation of receptors the number of receptors is decreased or receptors become desensitised due to continuous or prolonged exposure to an agonist.

The process of down regulation can occur in many different types of receptors, including those involved in neurotransmission, hormone signalling, and immune function. For example, prolonged use of opioids can lead to down regulation of the opioid receptors, reducing their sensitivity to the drug and requiring higher doses to achieve the same therapeutic effect.

Up regulation of receptors:

In up regulation of receptors the count of receptors is increased, happens when receptors activation is blocked for prolonged period mostly for few days by pharmacological antagonists or by denervation.

Up regulation can occur in many different types of receptors, including those involved in neurotransmission, hormone signalling, and immune function. For example, in patients with heart failure, the body may upregulate beta-adrenergic receptors to increase the heart’s responsiveness to sympathetic nervous system stimulation.

Functions of receptors:

  • To propagate signals from outside to inside.
  • Receptors enable cells to communicate with each other through the binding of signaling molecules, such as neurotransmitters, hormones, or growth factors.
  • To amplify the signal.
  • To integrate various extracellular and intracellular regulatory signals.
  • Receptors in sensory organs, such as the eyes, ears, and skin, detect changes in the environment and transmit this information to the brain for processing.
  • Receptors help regulate various physiological parameters, such as blood pressure, heart rate, and body temperature, to maintain the body’s internal balance.
  • Receptors on immune cells detect foreign invaders, such as viruses and bacteria, and initiate an immune response to eliminate them.
  • Receptors on cells involved in energy metabolism, such as the liver and adipose tissue, regulate the uptake, storage, and breakdown of nutrients.
  • Receptors play a critical role in the development and growth of the body, including cell proliferation, differentiation, and migration.
  • Receptors on muscle cells are involved in the initiation and regulation of muscle contraction.
  • Receptors on nerve cells are involved in the transmission of signals between neurons, allowing for communication within the nervous system.
  • Receptors in the brain are involved in the regulation of behavior and mood, and drugs that target these receptors can be used to treat conditions such as depression and anxiety.

Affinity and intrinsic activity:


Affinity is ability of a drug to bind to a receptor.

Intrinsic activity:

Intrinsic activity is the ability of a drug to produce a response after binding to a receptor.

Receptor Ligands


A drug that has affinity and intrinsic activity is called Agonist. An Agonist produces some of the effects of endogenous compounds when it interacts with receptor, for example isoproterenol at beta adrenoceptors.


A drug that has affinity but does not have intrinsic activity is called antagonist. Antagonist is a drug that binds to receptors without activating it, thereby blocking endogenus agonist from exerting its effect, for example propranolol at beta adrenoceptors.

Partial Agonist:

A drug that has affinity and some intrinsic activity is called partial agonist. for example nalbuphine. A partial agonist may act as either an agonist if full agonist is absent or an antagonist if full agonist is present.

Inverse agonist:

A drug that activates receptor to produce an effect in the opposite direction to that of the agonist, for example carbolines at benzodiazepine receptors.

Spare receptors:

When maximal pharmacological response can be elicited by an agonist at concentration that does not result in occupancy of all available receptors, the receptors that are not occupied or called spare receptors. Spare receptors are not Hidden and not unavailable and when they are occupied, can be coupled to response.

Drug receptor interactions:

Drug combines with the receptor and making a drug receptor complex this combination results in a sequence of events occurring intracellularly by which a drug receptor complex produce an effect.

Learn more

What is Receptor?

What is drug receptors?

Examples of drug receptors

Nature of drug receptors

What is regulation of receptors?

What is up regulation of receptors?

What is down regulation of receptors?

Functions of receptors

Top 10 Functions of receptors

What is affinity?

What is intrinsic activity?

Drug receptor interactions

What is spare receptors?

What is inverse agonist?

What is partial agonist?

What is antagonist ?

What is agonist?

What is Receptor Ligands?

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