Angiotensin I-converting enzyme modulates neutral endopeptidase activity in the rat

Angiotensin I is a substrate for both ACE and for neutral endopeptidase 24. 11 (NEP). We hypothesized that high ACE expression is related to low NEP ac tivity. Accordingly, circulating and tissue NEP and ACE activities were mea sured by fluorometry in homozygous rats (FO and 172) for the Lewis microsat ellite allele (LL, low ACE) and for the Brown Norway microsatellite allele (BB, high ACE). Plasma, lung, and aortic ACE activities in F-0 and F-2 were higher in BB rats than in LL rats (P <0.01), whereas left ventricular ACE activity was similar in both genotypes. In contrast, NEP activity in the LL group was higher in the serum, aorta, and lungs in F-0 and F-2 homozygous (P <0.05). Plasma ACE activity was inversely correlated with serum (r=-0.6 and -0.598 in F-0 and F-2, respectively; P <0.03) and lung NEP activities ( r=-0.77 in F-0 and r=-0.59 in F-2, P <0.01). Aortic ACE and NEP activities were also correlated (r=-0.696 and -0.584 in F-0 and F-2, respectively; P < 0.03). In conclusion, genetically determined high ACE expression in rats is inversely related to tissue NEP activity, which could determine lower angi otensin-(1-7) tissue levels.