The effect of a xanthine derivative, 1-(5' oxohexyl)-3-methyl-7-propylxanthine (HWA 285), on heart performance and regional blood flow in dogs and rabbits.

1. The effect of a new xanthine derivate 1-5' oxohexyl-3-methyl-7-propylxanthine (HWA 285) was studied on heart performance in dogs and rabbits and on regional blood flow in rabbits. 2. Heart performance (cardiac output and dP/dt max) in dogs was increased. Cardiac work (calculated as CO x mean BP) was not changed in dogs and did not change or was slightly decreased in rabbits. Heart rate was increased in dogs and unchanged in rabbits. 3. Blood pressure decreased slightly in dogs, and more markedly in rabbits. Total peripheral resistance was decreased in both species. 4. Regional blood flow (studied by use of 15 micrometers labelled microspheres) was increased in the heart, brain and skeletal muscle; the increase was dose-dependent in the range 0.3, 1.0 and 3.0 mg HWA 285 per kg intravenously. The highest dose produced a 2 fold decrease in the peripheral resistance in the brain, a 2.5 fold decrease in the heart and 4 fold decrease in skeletal muscle. 5. The drugs preferentially dilated small (7 to 10 micrometers) rather than larger (12 to 17 micrometers) arterioles; 9 micrometers microspheres were found in the outflowing blood after application of the drug, and the calculated blood flow increases were smaller, or absent, as compared with values obtained with 15 micrometer microspheres.