Sensitive method for quantitation of angiotensin-converting enzyme (ACE) activity in tissue

Compartmentalization of angiotensin II generation in the dog heart. Evidence for independent mechanisms in intravascular and interstitial spaces

Angiotensin-converting enzyme inhibitors have beneficial effects that are presumably mediated by decreased angiotensin II (ANG II) production. In this study, we measure for the first time ANG I and ANG II levels in the interstitial fluid (ISF) space of the heart. ISF and aortic plasma ANG I and II levels were obtained at baseline, during intravenous infusion of ANG I (5 microM, 0.1 ml/min, 60 min), and during ANG I + the angiotensin-converting enzyme inhibitor captopril (cap) (2.5 mM, 0.1 ml/min, 60 min) in six anesthetized open-chested dogs. ISF samples were obtained using microdialysis probes inserted into the left ventricular myocardium (3-4 probes/dog). ANG I increased mean arterial pressure from 102+/-3 (SEM) to 124+/-3 mmHg (P < 0.01); addition of cap decreased MAP to 95+/-3 mmHg (P < 0.01). ANG I infusion increased aortic plasma ANG I and ANG II (pg/ml) (ANG I = 101+/-129 to 370+/-158 pg/ml, P < 0.01; and ANG II = 22+/-40 to 466+/-49, P < 0.01); addition of cap further increased ANG I (1,790+/-158, P < 0.01) and decreased ANG II (33+/-49, P < 0.01). ISF ANG I and ANG II levels (pg/ml) were > 100-fold higher than plasma levels, and did not change from baseline (8,122+/-528 and 6,333+/-677), during ANG I (8,269+/-502 and 6, 139+/-695) or ANG I + cap (8,753+/-502 and 5,884+/-695). The finding of very high ANG I and ANG II levels in the ISF vs. intravascular space that are not affected by IV ANG I or cap suggests that ANG II production and/or degradation in the heart is compartmentalized and mediated by different enzymatic mechanisms in the interstitial and intravascular spaces.

Blood pressures and cardiovascular homeostasis in mice having reduced or absent angiotensin-converting enzyme gene function

We studied cardiovascular phenotypes in wild-type (+/+), heterozygous (+/-), and homozygous mutant (-/-) mice for an insertional inactivation of the angiotensin-converting enzyme (ACE) gene (Ace in mice, ACE in humans). Compared with +/+ mice, baseline mean arterial pressure was not significantly altered in +/- mice but was reduced by 51+/-4 mm Hg in -/- mice. Although the pressor response to injected angiotensin II did not differ significantly in the three genotypic groups, the pressor response to angiotensin I was strongly affected by Ace genotype: Compared with the response in the +/+ group (+26% of baseline), the response to Ang I was close to half normal (+12%) in the +/- group and virtually abolished (+1%) in the -/- group. The depressor response to injected bradykinin was significantly enhanced in the +/- and -/- groups compared with the +/+ group. Ace expression and ACE activity were directly related to functional Ace copy number, and renin and angiotensinogen mRNA levels were inversely related to Ace copy number. Angiotensin type 1A receptor mRNA levels were not significantly different in the +/+, +/-, and -/- groups. We conclude that (1) ACE is essential for the maintenance of normal blood pressure; (2) subnormal levels of ACE affect the blood pressure responses to infused angiotensin I and bradykinin in vivo; and (3) compensations for inactivation of one Ace copy, which include increased expression of renin, normalize blood pressure in heterozygotes.

Purification and assay methods for angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE; EN 3.4.15.1) is a peptidyl dipeptide hydrolase that removes the carboxyl terminal His-Leu from angiotensin I to produce the octapeptide angiotensin II. In addition, ACE inactivates bradykinin, a vasodilator peptide/mediator of inflammation, as well as substance P, enkephalins and endorphins. Because of the importance of ACE and its active site-directed inhibitors in the pathogenesis and treatment of cardiovascular disorders such as hypertension and heart failure, ACE purification and assay are of clinical and commercial, as well as scientific interest. This review summarizes the historical development of ACE purification and assay methods and presents some innovative high-performance liquid chromatography-based techniques developed in our own laboratory for high yield and efficient purification and sensitive and specific assay of ACE.