Figure 2.

Serial mean effects (± SEMs) of two concentrations of lethal toxin (LT, 50 or 500 ng/mL) compared with protective antigen alone (controls) administered to isolated perfused hearts excised from healthy animals on left ventricular developed pressure (LVDP, panel A), rate pressure product (RPP, panel B) and rate of change in LV pressure during contraction (dP/dt max, panel C). The shaded area represents the time of LT or control administration. The p-values shown are for the effect of LT versus control. Increases or decreases with LT (compared to controls) are indicated by symbols above or below the dashed horizontal no-effect line respectively. The LT concentration of 50 ng/mL was comparable to a dose previously shown to produce a 50% lethality rate in in vivo experiments. Although the concentration of 500 ng/mL did depress myocardial function, this represented a dose 10-fold greater than one producing lethality in vivo.