Myocardial and Renal Renin-Angiotensin System Enzyme Activity in Dogs.

Abstract

BACKGROUND: Methods to quantify the activity of the tissue renin-angiotensin system (RAS) are needed. OBJECTIVE: To estimate myocardial and renal RAS enzyme activity in postmortem tissues. ANIMALS: Convenience sample of 15 purpose-bred laboratory dogs with experimental heartworm infection (Group 1) euthanized as part of an unrelated study and 22 client-owned dogs which died or were euthanized for any reason (Group 2). METHODS: Prospective study where myocardial and renal tissue samples were frozen within 20&#x2009;min of euthanasia (Group 1) or during routine necropsy exam (Group 2). Homogenized tissues were incubated with spiked angiotensin I or II (AngII) under control and inhibitor conditions to assess relative enzyme contributions to AngII or angiotensin 1-7 formation. Freezing was delayed (2- or 7-h in Groups 1 and 2, respectively) in paired samples, to evaluate the effect of time to freezing on RAS enzyme activity. RESULTS: Samples were harvested within 20&#x2009;min of euthanasia (Group 1) or a median of 21.9&#x2009;h after death or euthanasia (Group 2). RAS enzymes were active in all samples. The median contribution of angiotensin-converting enzyme to AngII formation was greater than 88% in all tissues. The 90% confidence limits of the geometric mean of the ratio of the angiotensin production of paired samples in 10/14 (Group 1) and 16/19 (Group 2) experiments met equivalence requirements (lower bound >&#x2009;0.8 and upper bound <&#x2009;1.2). CONCLUSIONS AND CLINICAL IMPORTANCE: Renin-angiotensin system enzymes are present and active in canine myocardial and renal tissues for greater than 24&#x2009;h postmortem.