[The synthetic fragment of rabbit blastocyst peptide2 and its physiological significance relevant to the mechanism of implantation].

The amino acid sequence of purified rabbit blastocyst peptide2 (RBP2) was analyzed. It contains 54 amino acids and it's sequence from aa4 to aa34 is the same as the N-terminal sequence of uteroglobin. An active antigenic region consisting of 15 aa residues (aa20-aa34) of the RBP2 was selected and designated as a synthetic peptide fragment (SPF). The effect of SPF on lymphocyte proliferation was analyzed by immunocytochemical assay detecting BrdU incorporation in the cellular DNA. The results indicated that no obvious inhibitory effect of SPF on T cell proliferation at concentrations ranging from 80 to 320 micrograms/ml was observed, while RBP2 at the concentrations ranging from 20 to 160 micrograms/ml had a significant effect in a dose dependent manner, suggesting that the immuno-suppressive effect of SPF is less than that of RBP2. We have also observed that SPF at concentrations ranging from 45 to 180 micrograms/ml inhibited PGF2 alpha secretion in a dose dependent manner. On the other hand, the 3H-leucine incorporation of rabbit endometrium was enhanced by SPF (180 micrograms/ml) and this action was blocked by addition of protein inhibitory agent, actidine.