Cardiac and hemodynamic effects of S(-)- and (R(+)-DPI 201-106 and of racemic DPI 201-106 in conscious dogs.

The cardiac and hemodynamic effects of (+/-)-DPI 201-106 (0.6 mg/kg), S(-)-DPI (0.3 mg/kg), R(+)-DPI (0.3 mg/kg), and their vehicle were compared in chronically implanted conscious dogs. (+/-)-DPI and S(-)-DPI induced qualitatively and quantitatively similar effects, increasing LV dP/dt, cardiac output and stroke volume and reducing total peripheral resistance. In contrast, R(+)-DPI decreased only stroke volume. It is concluded that (a) the positive inotropic effects of (+/-)-DPI in vivo are caused by its S(-) enantiomer, and (b) the peripheral vasodilating effects of (+/-)-DPI may not be linked to the drug's calcium antagonist properties.