SOLVENT DRAG IN JEJUNAL ABSORPTION OF SALICYLIC ACID AND ANTIPYRINE OBTAINED BY IN SITU SINGLE-PASS RERFUSION METHOD IN RAT

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The in situ single-pass perfusion method in an individual rat was developed to discuss the solvent drag in drug intestinal absorption without the individual differences. In this method the apparent water influx (influx') was used as a measure of solvent drag in the same manner as the previous paper¹⁾. Consequently the sieving coefficients of salicylic acid and antipyrine in one rat are not significantly different from one but in the other are significantly smaller than one, resulting in 0.6-0.7 in average. And it was also shown that the reflection from the membrane in the solvent drag can be detected more precisely and efficiently by this method than the recirculating method in the previous paper. The D₂O absorption clearance (CL_D2O was equal to net water flux as estimated theoretically when the D₂O concentration in lumen was equal to that in plasma, indicating that D₂O can be absorbed by water absorption even in the absence of the concentration gradient. Estimating the real water influx from the net water flux obtained under such condition, the minimal contribution ratio of the solvent drag to the total absorption clearance of salicylic acid and antipyrine was calculated to be approximately 12%.