EFFECTS OF LONG-TERM TREATMENT WITH ENALAPRIL OR HYDRALAZINE ON THE RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM AND FLUID BALANCE IN DOGS WITH NATURALLY ACQUIRED MITRAL-VALVE REGURGITATION

Objective-To study long-term effects of enalapril, an angiotensin-conv erting enzyme inhibitor, and hydralazine, an arteriodilator, on renin- angiotensin-aldosterone system and fluid balance before and after admi nistration of furosemide. Animals-22 dogs with clinical signs of conge stive heart failure (CHF) attributable to mitral regurgitation. Proced ure-After initial examination, 12 dogs received enalapril and 10 recei ved hydralazine. Dogs were re-examined 3 weeks and 6 months after init ial examination. Furosemide was added after the 3-week examination, an d at 6 months, dogs had received furosemide for at least 4 months. Res ults-Angiotensin II and aldosterone plasma concentrations were low bef ore treatment, and only aldosterone became significantly decreased aft er enalapril monotherapy. Concentrations of both hormones and heart ra te increased in dogs receiving hydralazine monotherapy, and fluid rete ntion was evident. After long-term treatment with either of the 2 drug s together with furosemide, angiotensin II and aldosterone values incr eased in both groups. Natriuresis and kaliuresis developed in ail dogs , with greatest effect in those receiving enalapril and furosemide. Th ese dogs had decreased plasma sodium concentration, whereas potassium concentration was equally decreased in both groups. After 6 months, th e enalapril group, but not the hydralazine group, had increased cardia c size. All dogs had moderate reduction of weight and were azotemic, a lthough changes were more pronounced in those of the hydralazine group . Conclusion-The 2 drugs have different effects on the renin-angiotens in-aldosterone system and fluid balance in dogs with CHF.