Question

Sir Henry Dale was noticed that adrenalin decreases blood pressure if another unknown agent is administered to the organism before the administration of adrenalin. The same dose of adrenalin increases blood pressure sharply if there is no pre administration of this unknown agent and when the unknown agent is admistered alone, no significant change in blood pressure is observed.
Discuss this experiment based on your knowledge about physiological activity of adrenalin, adrenergic receptors and pharmacodynamic drug interaction principles. What kind of an action could this unknown agent exert, which type of receptors migh it be acting on and how may it affect its receptors (agonist, antagonist, inverse agonist etc.)

Answer 1

This unknown agent act as inverse agonist which binds with the same receptors on which adrenaline binds (adrenergic receptors).

An inverse agonist is a compound that binds with the same receptors as an agonist but shows an opposite pharmacological response. Binding of agonist with its receptors results into increase in the activity of a receptor above its basal level, whereas binding of an inverse agonist results in decrease in the activity of receptors below the basal level.