Different Transfers of N-Acetyl-p-Aminobenzoic Acid and p-Aminobenzoic Acid Across the Placenta and the Small Intestine in Rats

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Abstract
The aim of the present study was to evaluate the transfer of N-acetyl-p-aminobenzoic acid (AcPABA) across the rat term placenta and the rat small intestine and to compare it with that of its parent drug p-aminobenzoic acid (PABA). Umbilical perfusion of the rat term placenta was used to determine the materno-fetal transfer. AcPABA appeared in the fetal compartment significantly more slowly than PABA (ktransfer = 0.023 and 0.064 min-1, respectively). The rate of equilibration between the maternal and fetal compartments was slightly lower for AcPABA than for the parent drug (kequilibrium = 0.0082 and 0.011 min-1, respectively). Similarly, AcPABA was shown to be absorbed from the small intestine significantly more slowly than PABA (ka = 0.052 and 0.82 min-1; tmax = 37 and 3.1 min, respectively). Our results showed that both investigated compounds which are structurally related and very similar in their physical-chemical characteristics crossed both the placental and small intestinal barrier with a different kinetics. AcPABA was transported across both barriers significantly more slowly than its parent compound, which might indicate a possible equipment of the placenta with a carrier for PABA, a similar one to that previously found in the rat small intestine.