The effect of tyramine and propranolol on contraction force of the control and sympathectomized rats. A,B. Contraction force (CF) of papillary muscles from the right (RV) and left ventricles (LV) in control rats (n=6). C, D. Contraction force (CF) of papillary muscles from the right (RV) and left (LV) ventricles in syrnpathectomized rats (n=5). Values were normalized to the CF in tyramine-free solution (taken as 100%). Stimulation frequency was 1 Hz. D = age in days. P = administration of propranolol (10-4 mol/l) on top of tyramine (10-4 mol/l). *p