Abstract
Ouabain was examined for effect on the mechanical response of the ileum isolated from eleven animal species, dog, cat, rabbit, guinea pig, rat, vole, mouse, cock, pigeon, frog and toad. In isotonic recording, ouabain induced a sustained contraction in ileum isolated from some species. It caused a transient contraction on following by a relaxation in others. The ouabain sensitivities of a contractile response in the ilea from eleven species, as demonstrated by the estimation of ED50, was divided into four groups. That is, a high sensitive group; frog (ED50=9.0×10-8M), cat (9.3×10-8M), pigeon (3.5×10-7M) and cock (5.1×10-7M), a sensitive group; rabbit (1.1×10-6M), vole (2.3×10-6M) and guinea pig (2.7×10-6M), a low sensitive group; mouse (1.7×10-5M) and rat (9.7×10-5M) and an insensitive group; toad (>10-3M). Although ED50 in the dog was not able to be calculated, its sensitivity seems to belong to the high sensitive group. On the other hand, ED50 of acetylcholine (Ach) in thc ilea, isolated from these species were estimated in a narrow range of concentration from 5×10-9M to 5×10-8M. There were species differences in ouabain sensitivity for ileal contractile response but not in Ach sensitivity. A distinct correlation was found between the mechanical response to ouabain and the inhibitory potency of ouabain for Na, K-ATPase reported by Repke et al. These results seem to confirm that ouabain may induce a contraction by a mechanism which inhibits an electrogenic Na pump or Na, K-ATPase in the intestinal smooth muscle cell and which induces a depolarization.
