Cardiovascular effects of aminophylline and pentoxifylline on intact dogs and isolated dog atria.

The effects of aminophylline and pentoxifylline were investigated on the blood pressure and heart rate in the intact dog and on the atrial rate and contractile force in isolated atrial muscle which was perfused with arterial blood of the donor dog. Firstly, each drug was intravenously administered to the donor dog. Both compounds produced a dose-dependent hypotension. Aminophylline frequently caused bradycardia in intact dogs and positive chrono- and inotropic effects in isolated atria. However, pentoxifylline usually produced only tachycardia in the donor dog and positive chrono- and inotropic effects on the isolated atrium. When the compounds were administered into the sinus node artery, positive chrono- and inotropic effects were induced, with aminophylline being approximately 3--10 times more potent than pentoxifylline. Larger doses of aminophylline or pentoxifylline when administered intravenously might cause a release of catecholamine, because increased sinus rate and developed tension in isolated atria which was perfused with donor's blood were partially, but significantly, suppressed by propranolol treatment. In the isolated atrium, aminophylline, but not pentoxifylline, significantly inhibited the negative chronotropic and inotropic effects of adenosine.