EVALUATION AS A BIOASSAY PREPARATION OF TORTOISE INTESTINE FOR PROSTAGLANDIN $E_1$

The isolated strips of tortoise intestine are evaluated as a test organ for bioassay of prostaglandin $E_1$. This preparation responded highly sensitively to $PGE_1$ and $PGE_2$ in picogram concentration range. The mean slope and the value of precision index among the doses of 0.1, 0.3 and 0.5ng/ml in final concentration were 37.7 and 0.143, respectively. And this was relatively insensitive to different prostaglandins; $E_1/E_2{\gtrsim}1$, $E_1/A_2{\sim}50$ and $E_1/F_{2\alpha}{\sim}100$, and showed the dual responses to 5-hydroxytryptamine and histamine; initial contraction followed by relaxation. The dose-ratio inducing the relative equal contraction height for $PGE_1$, acetylcholine, caerulein, angiotensin and barium chloride was 0.4 : 50 : 25 : 10 : 100 in this order. These results suggest that the intestinal strips of the tortoise are suitable for bioassay of prostaglandin $E_1$ and $E_2$ between the doses of 0.1 and 1.0 ng/ml level in the tissue extracts.