Rhomotoxin is a pharmacologically active principle isolated from the fruits of Rhododendron molle G. Don. Clinical experience demonstrated that it had an antihypertensive effect. In the present work, its haemodynamic effects were studied in anaesthetized open-chest dogs.
| 1. | Rhomotoxin given intravenously (5 μg/kg) lowered the blood pressure, slowed the heart rate and decreased the left ventricular pressure in dogs. In addition, it decreased ±dp/dt max significantly, which indicated that rhomotoxin might be inhibitory to cardiac contractility. This cardiac inhibitory effect was found to be parallel to its hypotensive action. |
| 2. | There is no simultaneous increase, sometimes even a decrease, in left ventricular end diastolic pressure, during the inhibition of contractile performance of the heart by the drug. Hence it was suggested that rhomotoxin might dilate the capacity blood vessels, decrease blood return to the heart and thus decrease the preload of the left ventricle. |
| 3. | The drug had a transient effect in lowering the peripheral blood vessel resistance, which, as shown by intra-femoral artery injection, was not due to its direct vasodilating action. |
| 4. | The haemodynamic effects of rhomotoxin were essentially the same in either vagotomized or intact animals. Thus it seemed unlikely that the action of vagus nerve played any important role in its antihypertensive action. |