Oral absorption, tissue distribution and excretion of a radiolabelled analog of a milk-derived antihypertensive peptide, Ile-Pro-Pro, in rats

Milk-derived bioactive peptides have been shown to attenuate the development of hypertension in rats and reduce blood pressure in humans. The aim of the present study was to examine the absorption, tissue distribution and excretion of intact Ile-Pro-[14C]Pro in rats. Radioactivity was determined in blood and tissues. After oral administration, Ile-Pro-[14C]Pro was absorbed from the intestine and the peak level was observed after 2 h. Considerable amounts of radioactivity were found by liquid scintillation in tissues, e.g., in the liver, kidneys, adrenals and aorta. Chromatographic and mass spectrometric analyses of plasma samples proved that Ile-Pro-[14C]Pro was present in all samples analysed. The majority of the radioactivity was associated with plasma proteins and in vitro tests showed that Pro-Pro attaches to plasma proteins (over 98%) whereas Ile-Pro-Pro is not bound. In conclusion, Ile-Pro-[14C]Pro is partly absorbed intact and the distribution of radioactivity in tissues may be related to the blood-pressure-lowering effect of the peptide.