A PEPTIDE RELEASED BY PEPSIN FROM KININOGEN DOMAIN-1 IS A POTENT BLOCKER OF ANP-MEDIATED DIURESIS-NATRIURESIS IN THE RAT

A 20-amino acid peptide, KYEIKEGDCPVQSGKTWQDC (PU-D1), released by pep sin hydrolysis of LMW kininogen domain 1 was tested for its ability to antagonize the diuretic and natriuretic effect of ANP(103-125) in ane sthetized rats. A single dose of 10.8 or 21.6 pmol (25 or 50 ng) PU-D1 given intravenously or into the duodenal lumen suppressed the diuresi s-natriuresis induced by 209 pmol (500 ng) ANP by 43% to 59% and 69% t o 96%, respectively. None of the doses tested (2.16 to 432 pmol, 5 ng to 1 mu g) modified systemic blood pressure. Strikingly, a single IV d ose of 10.8 pmol PU-D1 blocked the action of ANP for more than 3 hours . ANP blockade by PU-D1 was annulled completely by the bradykinin (BK) B2 receptor inhibitor Hoe 140. On a molar basis, PU-D1 is more effect ive than BK and kinins of 15, 16, and 18 amino acids for blocking the ANP-mediated diuresis-natriuresis. As with BK and other kinins, the in hibitory effect of Pu-D1 on ANP is obtained only within a small range of picomol doses. A single dose of 2.16 or 4.32 pmol PU-D1 or 47 pmol (50 ng) BK is ineffective against ANP if injected alone. However, when both substances are administered concomitantly at these subthreshold doses, they totally suppress ANP-induced diuresis-natriuresis. These r esults raise the question of whether PU-D1, released from kininogen do main 1, either alone or associated with BK, may interact with ANP in t he regulation of urinary water and electrolyte excretion in physiologi cal and pathological conditions.