1. The isolated strips of guinea-pig, fowl and reptiles (snake and tortoise) showed consistenly excitatory responses to PGE<sub>1</sub> and E<sub>2</sub>, which were dose-dependent. 2. Frog intestine revealed inhibitory responses to both PGE<sub>1</sub> and PGE<sub>2</sub> except a small of PGE<sub>2</sub> (1-10 ng/ml) caused slight contraction. 3. The intestines of pieces showed inconsistent responses to PGE<sub>1</sub> and E<sub>2</sub>. In fresh-water fish(carp), PGE<sub>1</sub> produced relaxation under the dose of 50 ng/ml, and contraction by the large doses, but PGE<sub>2</sub> consistently caused contraction in dose-dependent manner. However, the strips of sea-water fish revealed the different responses to PGE compound: PGE<sub>1</sub> caused relaxation and PGE<sub>2</sub> conversly contraction even though in small degree. 4. These results that there are genera differences in the responses of the longitudinal strips of intestine to PGE<sub>1</sub> and PGE<sub>2</sub> was assumed to be possibly correlated with evolutionally primitive function of gut.
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