COMPARISON BETWEEN KINETICS OF POSITIVE I NOTROPISM OF IBOPAMINE AND OUABAIN

AIM: To compare the kinetics of positive inotropism between ibopamine (Ibo) and ouabain (Oua). METHODS: The isolated right papillary muscle of cat was used to assess the positive inotropic effects by cummulativ e concentrations of Ibo and Oua. The maximal effects was recognized as the contraction just before the appearance of spontaneous contraction . A Hill equation was developed by using Ig [E/(E(max) - E)] vs Ig C. RESULTS: The S value of Ibo was smaller than that of Oua, causing C-95 /C-5 (ratio of concentrations producing 95%/5% of E(max)) of Ibo (264) elevenfold as large as Oua (22.9). Comparing with Oua, concentrations of Ibo initiating effects were lower, the slope was smaller, and high er concentrations were required for producing maximal effect. During d rug concentration declining, the effect-concentration curve of Ibo sho wed a counter-hysteresis loop, more remarkable than Oua. CONCLUSION: T he changes in positive inotropism of Ibo against drug concentrations w ere less than those of Oua.