The di/tri-peptide transporter h-PEPT1 plays an important role in the oral absorption of di/tri-peptides and numerous drugs. Inflammatory conditions may influence intestinal xenobiotic transporter function; however, the effects of inflammation on h-PEPT1 have not been well described. This study was conducted to determine the effects of the inflammatory cytokine interferon-gamma (IFN-gamma) on h-PEPT1 mediated dipeptide absorption. Caco-2 monolayers were grown on permeable supports. The effective apical-to-basolateral permeability (P(eff)) of glycylsarcosine (Gly-Sar) was measured following incubation with IFN-gamma or control media. Additional experiments were conducted at 4 degrees C, and with escalating concentrations of Gly-Sar. h-PEPT1 expression was determined using semiquantitative RT-PCR. IFN-gamma 50 ng/ml increased Gly-Sar P(eff) 28.6% compared to controls (p=0.03). In experiments conducted at 4 degrees C, Gly-Sar P(eff) decreased 39.6% in IFN-gamma treated cells (p=0.003) and 28.4% in controls (p=0.006). In controls and IFN-gamma treated cells, concentration dependent transport was seen with escalating concentrations of Gly-Sar. Compared to controls, IFN-gamma 50 and 100 ng/ml increased h-PEPT1 mRNA expression by 14.2% and 11.5%, respectively (p=0.019). In summary, IFN-gamma increases h-PEPT1 expression and permeation of the dipeptide Gly-Sar in Caco-2 monolayers. These findings imply that intestinal absorption of peptides and peptidomimetic drugs may be increased in certain inflammatory conditions.