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-converting enzyme inhibitor, and hydralazine, an arteriodilator, on renin-angiotensin-aldosterone system and fluid balance before and after administration of furosemide.


METHODS
22 dogs with clinical signs of congestive heart failure (CHF) attributable to mitral regurgitation.


METHODS
After initial examination, 12 dogs received enalapril and 10 received hydralazine. Dogs were re-examined 3 weeks and 6 months after initial examination. Furosemide was added after the 3-week examination, and at 6 months, dogs had received furosemide for at least 4 months.


RESULTS
Angiotensin II and aldosterone plasma concentrations were low before treatment, and only aldosterone became significantly decreased after enalapril monotherapy. Concentrations of both hormones and heart rate increased in dogs receiving hydralazine monotherapy, and fluid retention was evident. After long-term treatment with either of the 2 drugs together with furosemide, angiotensin II and aldosterone values increased in both groups. Natriuresis and kaliuresis developed in all dogs, with greatest effect in those receiving enalapril and furosemide. These dogs had decreased plasma sodium concentration, whereas potassium concentration was equally decreased in both groups. After 6 months, the enalapril group, but not the hydralazine group, had increased cardiac size. All dogs had moderate reduction of weight and were azotemic, although changes were more pronounced in those of the hydralazine group.


CONCLUSIONS
The 2 drugs have different effects on the renin-angiotensin-aldosterone system and fluid balance in dogs with CHF.
Department of Physiology, Faculty of Veterinary Medicine, University of Agricultural Sciences, Uppsala, Sweden.
J
J
Häggström
K
K
Hansson
B E
BE
Karlberg
C
C
Kvart
A
A
Madej
K
K
Olsson
D000450:Aldosterone / Q000097:blood; D000804:Angiotensin II / Q000097:blood; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000627:therapeutic use*; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D004283:Dog Diseases / Q000188:drug therapy* / Q000503:physiopathology; D004285:Dogs; D004452:Echocardiography; D004656:Enalapril / Q000627:therapeutic use*; D005260:Female; D005665:Furosemide / Q000627:therapeutic use; D006333:Heart Failure / Q000662:veterinary; D006339:Heart Rate / Q000187:drug effects; D006830:Hydralazine / Q000627:therapeutic use*; D008297:Male; D008944:Mitral Valve Insufficiency / Q000188:drug therapy / Q000503:physiopathology / Q000662:veterinary*; D012084:Renin-Angiotensin System / Q000187:drug effects* / Q000502:physiology; D014665:Vasodilator Agents / Q000627:therapeutic use*; D014882:Water-Electrolyte Balance / Q000187:drug effects*
D000806:Angiotensin-Converting Enzyme Inhibitors; D014665:Vasodilator Agents; D000804:Angiotensin II; D006830:Hydralazine; D000450:Aldosterone; D004656:Enalapril; D005665:Furosemide