Today's Veterinary Practice

MAR-APR 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 28 CE: CARDIOVASCULAR AND RENAL DISEASE The RAAS This system, the release of renin, angiotensin II, and aldosterone, is one of the most potent endocrine systems in the body and plays a key role in survival from acute injury or illness. Through widespread vasoconstriction triggered by angiotensin II and aggressive kidney reclamation of sodium and water, the RAAS helps restore and maintain blood pressure and volume. Although the RAAS is a life-saving response in emergent circumstances, it can become maladaptive over time if the GFR decrease is not due to a decrease in blood volume. For example, a dog with dilated cardiomyopathy and reduced cardiac output will deliver less blood to the kidneys, despite an excess in total body volume. Decreased renal perfusion activates the RAAS, leading to vasoconstriction and inappropriate sodium and fluid retention. Vasoconstriction and volume retention may help restore GFR but adversely affect the heart and contribute to congestive heart failure (CHF). Other Interactions Although the RAAS is one of the major ways in which the kidneys and heart interact, they interact in other ways as well. Common processes associated with renal disease (eg, anemia, systemic hypertension, hypokalemia, or a hypercoagulable state) can negatively affect the cardiovascular system. Medical therapies designed to support one system may be deleterious to the other. For example, diuretic therapy to manage CHF in an azotemic animal with renal disease may further decrease GFR through volume depletion. In patients with renal disease, changes in blood flow and glomerular filtration may affect drug metabolism and clearance of drugs given for cardiovascular disease (eg, digoxin), resulting in increased risk for toxicity. Renin Angiotensin I Angiotensinogen Aldosterone Sodium and water retention Vasoconstriction Angiotensin II FIGURE 1. Renin-angiotensin-aldosterone system. Adrenal Gland Kidney Kidney

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