Tachycardia in spontaneously hypertensive and normotensive rats after fusaric acid and bupicamide.

1. The effects of the dopamine-beta-hydroxylase inhibitors bupicamide, fusaric acid, FLA-63 and U-14,624 on blood pressure and heart rate of spontaneously hypertensive rats were examined. 2. Bupicamide and fusaric acid caused marked tachycardia whereas FLA-63 and U-14,624 caused modest bradycardia; all drugs decreased blood pressure. 3. In normotensive rats, fusaric acid caused the same degree of tachycardia as in spontaneously hypertensive rats, but blood pressure was only slightly reduced. 4. Tachycardia after fusaric acid was not due to increased sympathetic activity or decreased parasympathetic activity but required intact catecholamine stores. 5. It is concluded that fusaric acid causes tachycardia by releasing catecholamines indirectly and that a metabolite of fusaric acid is also involved.