Graded dose—response

Abstract

The dose—response relation of many agonists yield sigmoidal (S-shaped) curves when the response is plotted against the logarithm of the dose (see Figure 8.1). There is no generally accepted theory that explains the shape of such curves; yet, we find that such curves are often approximately linear between 20% and 80% of the maximum response. In particular, many isolated tissue preparations display this linear segment. The data in the 20%–80% region may therefore be subjected to linear regression as given in Procedure 3, in which y = effect, or percent effect, and x = log dose. The regression line so determined might be used in the comparison of potency (Procedure 10) or in the analysis of the action of a competitive antagonist (Procedure 15). In each of these applications the regression lines are made parallel, and equieffective doses are determined.