Figure 5: A. The Waud method. Mean (n=5) concentration-response curve for the increases in rate of guinea-pig atria to isoprenaline () and prenalterol ( (۞ plotted as a percentage of the isoprenaline maximum. B. Double reciprocal plots of equieffective concentrations of isoprenaline (1/A) and prenalterol (1/P) obtained from the mean plot in A.