Comparative effects of ouabain on isolated papillary muscle from tree shrews, guinea-pigs and rats

Inotropic effects of ouabain were investigated in the isolated papillary muscle preparations of the tree shrew (Tupaia glis), guinea-pigs and rats. In the guinea-pig and shrew papillary muscles, ouabain at concentrations of 10(-8) to 3 x 10(-7) M caused a concentration-dependent positive inotropic response in a similar magnitude, while in the rat, ouabain at concentrations of 10(-7) to 3 x 10(-6) M elicited negative inotropic one. Either phentolamine or pindolol in a concentration sufficient to block the alpha- and beta-adrenoceptors did not antagonize the positive inotropic effect of ouabain in the papillary muscle preparation of the shrews.