VASCULAR ANGIOTENSIN-CONVERTING ENZYME EXPRESSION REGULATES LOCAL ANGIOTENSIN-II

We tested the hypothesis that changes in angiotensin-converting enzyme (ACE) gene expression can regulate the rate of local vascular angiote nsin II (Ang II) production. We perfused isolated rat hindlimbs with a n artificial medium and infused renin and Ang I via the perfusate. Ang I and II were measured by radioimmunoassay. We then increased ACE gen e expression and ACE levels in the rat aorta by producing two-kidney, one clip (2K1C) hypertension for 4 weeks. Gene expression was measured by RNAse protection assay, and ACE activity in the vessel wall was me asured by the Cushman-Cheung assay. Angiotensin I infusion at 1, 10, 1 00, and 1000 pmol/ml led to 371+/-14 (+/-SEM), 3511+/-202, 44 828+/-14 25, and 431 503+/-16 439 fmol/mL Ang II released, respectively, from t he hindlimbs (r=.98, P<.001). Thus, the conversion rate did not change across four orders of magnitude, and the system was not saturable und er these conditions. In 2K1C hindlimbs, Ang I infusion (0.5 pmol/ml) r esulted in increased Ang LI generation (157+/-16 versus 123+/-23 fmol/ mL, P=.014 at minute 10) compared with controls. ACE gene expression a nd ACE activity were increased in 2K1C hindlimbs compared with control s (36+/-4 versus 17+/-1 mU/mg protein, P<.001). Ang II degradation in the two groups did not differ. To investigate the conversion of locall y generated Ang I, we infused porcine renin (0.5 milliunits per mt) in to 2K1C and control hindlimbs. Despite markedly higher Ang I release i n sham-operated than in 2K1C rats (71+/-8 versus 37+/-6 pmol/mL, P=.00 8 at minute 12), Ang II was only moderately increased (36+/-3 versus 2 5+/-6 pmol/ml, P=.12 at minute 12). This difference between 2K1C rats and controls reflected a higher rate of conversion in 2K1C rats. Thus, Ang I conversion in the rat hindlimb is linear over a wide range of s ubstrate concentrations and occurs at a fixed relationship. Neverthele ss, increased ACE gene expression and ACE activity in the vessel wall lead to an increase in the conversion of Ang I to Ang II. We conclude that local ACE gene expression and ACE activity can influence the loca l rate of Ang II production.