Efficacy I: a new method for estimating relative efficacy of full agonists via a newly defined efficacy related parameter

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 ( e ES) and it may be estimated without prior knowledge of efficacy values or the value of the equilibrium dissociation constants, K A, of agonist-receptor complexes. The parameter e ES is directly related to efficacy ( e) and is defined as the ratio of maximal stimulus to maximal effect of an agonist. The value of e ES indicates whether or not spare receptors are present for a particular agonist–effector system. The e ES 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 e ES, other new agonist–effector parameters, namely S Em / S m and φ min, were also defined.