USE OF AN ANTAGONIST FOR ESTIMATING THE DEGREE OF AGONIST STIMULATIONDURING PHYSIOLOGICAL RELEASE

Antagonist activity can he measured either as the percentage reduction in the effect of an agonist or as a dose ratio. In this article, Dick Barlow explains how these are connected and how the relationship betw een the concentration of antagonist producing 50% inhibition (IC50) an d the antagonist equilibrium constant (K-i) involves the degree of ago nist stimulation ([A]/[A(50)]), which is the concentration of agonist expressed as a multiple of the concentration producing a half-maximal response. If K-i is known it is possible to use the IC50 value of the antagonist to estimate the degree of agonist stimulation in physiologi cal experiments where there is neuronal or hormonal release of the ago nist.