Polish Pharmaceutical Society Angiotensin-converting enzyme (ACE), neu-

tral endopeptidase (NEP) and aminopeptidase N (APN) are zinc metallopeptidases located on the outer membrane of different cells (entoenzymes). They play an important role in the metabolism of a number of regulatory peptides of human nervous, cardiovascular, inflammatory, and immune sys-tems. ACE (EC 3.4.15.1) is a dipeptidyl carboxy-petidase that converts angiotensin I to angiotensin II (AngII) and degrades kinins. ACE plays a central role in the rennin-angiotensin-aldosterone system (RAAS) (1). Neutral endopeptidase (NEP; EC 3.4.24.11) catalyses the degradation of variety of renal and CNS-active peptides including substance P, bradykinin, enkephalins, atrial natriuretic pep-tides, endothelin, and AngII. Selective NEP inhibi-tors further enhance the increase of atrial natriure-tic peptide (ANP) concentration in plasma and uri-nary excretion of ANP, cyclic GMP and sodium (1, 2). Dual ACE/NEP inhibitors were developed and investigated as a new therapeutic approach in the treatment of hypertension, heart failure and other cardiovascular diseases (3). Interestingly, recently performed research revealed that changes of neu-tral endopeptidase expression are implicated in the progression of prostate cancer (4). In contrast to NEP and ACE, rather specifically acting enzymes, aminopeptidase N (APN; EC 3.4.11.2) is an α-ami-noacylpeptide-hydrolase with a low substrate spe-cificity. The change in expression of APN plays an important role in the invasion and metastasis of cancer cells, and in immuno-modulating activities (5, 6). The aim of this study was to evaluate inhibito-ry potency o several plant extracts on metallopep-tidases. The medicinal plants selected for this trial are used as diuretics in the treatment of urinary tract diseases or in carciovascular diseases. Bucco folium, Callunae flos, Equiseti herba, Graminis rhizoma, Hernariae herba, Juniperi fruc