Related Experiment Video
Updated: Jul 12, 2026

Quantifying Agonist Activity at G Protein-coupled Receptors
Published on: December 26, 2011
Efficacy. I: A new method for estimating relative efficacy of full agonists via a newly defined efficacy related
1Department of Pharmacology, Potchefstroom University for Christian Higher Education, South Africa. fkldpv@puknet.puk.ac.za
Abstract:
A new method for estimating relative efficacies and relative intrinsic efficacies of agonists is described. Relative efficacy is estimated by employing a newly defined efficacy related parameter (eES) and it may be estimated without prior knowledge of efficacy values or the value of the equilibrium dissociation constants, KA, of agonist-receptor complexes. The parameter eES is directly related to efficacy (e) and is defined as the ratio of maximal stimulus to maximal effect of an agonist. The value of eES indicates whether or not spare receptors are present for a particular agonist-effector system. The eES values of agonists are estimated by utilizing submaximal concentration-effect curves determined with fixed agonist-competitive antagonist concentration combinations and choosing a suitable reference (height of an agonistic concentration-effect curve) to which the height of the stimulus concentration-effect curves of the agonist may be compared. In addition to eES, other new agonist-effector parameters, namely SEm/Sm and phi min, were also defined.
Related Concept Videos
Dose-Response Relationship: Overview
Dose-Response Relationship: Potency and Efficacy
Adrenergic Agonists: Chemistry and Structure-Activity Relationship
Aromatic ring substitutions: Substituting the aromatic ring with –OH groups at positions 3 and 4 yields catecholamines (e.g., epinephrine), which have a high affinity for adrenoceptors. Hydrogen bonding between –OH groups and receptors enhances adrenergic activity.
Separation of the aromatic...
Measurement of Bioavailability: Pharmacodynamic Methods
Pharmacodynamic Models: Linear Concentration–Effect Model

