Effects of 4 classes of cardiovascular drugs on ventricular function in dogs with mitral regurgitation.
BACKGROUND
There have been few trials in which dogs with mitral regurgitation (MR) have been treated with various cardioactive drugs to determine effects on left ventricular (LV) function.


OBJECTIVE
Four classes of cardiovascular drugs may improve LV function in dogs with MR without increasing MR.


METHODS
Nine mature dogs were included in the study.


METHODS
MR was produced in 9 dogs. Five months later under butorphanol narcosis, parameters of LV function and left atrial dimension (LAD) were monitored by LV micromanometry and echocardiography/Doppler. Dogs were given (in random order) enalaprilat, nitroglycerine, ouabain, milrinone, and placebo.


RESULTS
Nitroglycerin produced no significant change; milrinone and ouabain increased contractility; ouabain decreased heart rate; and there was evidence that enalaprilat and milrinone decreased LAD. Milrinone and ouabain decreased isovolumetric contraction time and therefore the time available for MR. There was no evidence that a positive inotrope increased MR despite increasing LV contractility and stroke volume.


CONCLUSIONS
This study contradicts the hypotheses that (1) strengthening the left ventricle may increase MR and (2) treatment of MR (even before symptoms of heart failure develop) may decrease LAD. It is reasonable that strengthening the force of LV contraction should increase the driving pressure for MR; however, this effect did not appear to increase MR. Although some investigators believe that treating dogs with MR with afterload reducers and decreasing hindrance to ejection of blood from the LV to aorta may lengthen life by decreasing MR, there did not appear to be a reduction in MR, at least in response to the angiotensin-converting enzyme (ACE) inhibitor.
Nakayama
Tomohiro
T
Department of Veterinary Biosciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210, USA.
Nishijima
Yoshinori
Y
Miyamoto
Mutsumi
M
Hamlin
Robert L
RL
D000806:Angiotensin-Converting Enzyme Inhibitors / Q000494:pharmacology*; D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D004195:Disease Models, Animal; D004283:Dog Diseases / Q000188:drug therapy*; D004285:Dogs; D015773:Enalaprilat / Q000494:pharmacology; D005260:Female; D008297:Male; D020105:Milrinone / Q000494:pharmacology; D008944:Mitral Valve Insufficiency / Q000188:drug therapy / Q000662:veterinary*; D005996:Nitroglycerin / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D011897:Random Allocation; D016896:Treatment Outcome; D016277:Ventricular Function, Left / Q000187:drug effects*; D020257:Ventricular Remodeling / Q000187:drug effects
D000806:Angiotensin-Converting Enzyme Inhibitors; D002316:Cardiotonic Agents; D010042:Ouabain; D005996:Nitroglycerin; D015773:Enalaprilat; D020105:Milrinone