Abstract
The causes of the difference in the permeability from the intestinal lumen to the serosal compartment between salicylamide(SAM)and benzoic acid(BA) has been studied from the point of view of the plasma protein-binding, the blood-to-plasma concentration ratio (RBP), the pH effect and the solvent drag effect. Latter two effects were also tested for salicylic acid (SA), p-hydroxy-benzoic acid (HBA), phenacetin (PHT) and antipyrine (AP).The protein binding and RBP were not the reason of the difference in the intestinal permeabilities. The effects of pH and tonicity of the perfusion solut ion on the drug permeability into the blood (CLB) and into the serosal compartment (CLS) were determined. CLS of SAM and CLB of BA obeyed the pH partition theory. But, CLB of SAM and CLs of BA was not affected by the pH. Tonicity also did not significantly affect the permeabilities of SAM to the blood and to the serosal compartment. However, CLB of BA was incr eased by the hypotonicity indicating the existence of the solvent drag effect. CLS of BA was not affected by the tonicity. SA and HBA showed the same character as BA. PHT and AP had a considerable permeability to the serosal compartment and AP was reported to be transported to the serosal compartment.It was concluded that BA as well as SAM permeated the mucosal membrane of intestinal cells, and then they were transported to the blood or to the serosal compartment. The ratio of BA transported to the blood/to the serosal compartment was much larger than that of SAM. BA was transported to the blood by the solvent drag, while SAM was not. Consequently the portion of BA transported to the serosal compartment was little, while that of SAM was considerable. This discrepancy was caused by the characters of drug ; such as 1) the permeability of the serosal membrane of the intestine, 2) the liability to be carried by the solvent drag.
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