The invention includes a method of reducing urea concentration in a subject'sserum. Such a method comprises administering to the subject (e.g., a mammalsuch as a human) a composition comprising an oligopeptide (or oligopeptides)having activity in reducing urea concentration in the subject's serum asdetermined by a mouse renal reperfusion test, wherein the oligopeptidecomprises the sequence QGV or MTRV (SEQ ID NO:1) (e.g., AQGV (SEQ ID NO:2) orMTRV (SEQ ID NO:1)).