Inotropic response to isoproterenol. Effect of the β-adrenergic agonist isoproterenol in increasing concentrations from 10-8 to 10-2 M on force development in isolated left ventricle papillary muscles from Sham operation (Sham) and ovariectomized (Ovx) rats at 7, 15, 30 and 60 days after surgery. Extracellular Ca2+ concentration was 0.62 mM. Force (g/g) values are expressed as mean ± S.E.M. *different from sham (P < 0.05) using two-way ANOVA and post hoc Tukey test. Number of animals used is indicated.