Abstract
When Danielli's model, the transition state theory and the formal treatment on the basis of the extrathermodynamic relationships were applied to the intestinal absorption of foreign organic compounds, it was expected that there should be the following relation between the absorption rate coefficients for the compound (RS) having a substituent group (S) and for the mother compound (RH). log kRS/kRH=constant The perfusion experiments through the small intestine of anesthetized rats for a number of benzene derivatives were carried out. The logarithmic plots of the residual ratio against the perfusion time gave straight lines and from the slopes the absorption rate coefficients were obtained. The results indicate that the values of log kRS/kRH for a given substituent group (S) have a proper value which is called the substituent constant.
