Centrally active drugs and the medullary vasopressor response of the cat; a method of distinguishing between drug actions on the central and peripheral parts of the sympathetic nervous system

1. A method is reported for the simultaneous study of the central and peripheral actions of drugs on the pressor response to electrical medullary stimulation in cats anaesthetized with chloralose.

2. Variations in the magnitude of the medullary vasopressor response were reduced by stabilization of the blood pressure using a reservoir of dextran solution connected to the venous circulation. Results were qualitatively the same with or without stabilization. Decreasing the body temperature over the range 39.5–32°C produced a linear and reversible decrease in the medullary vasopressor response. This response was slightly reduced by bilateral adrenalectomy.

3. Benactyzine, hydroxyzine and mebutamate depressed the medullary vasopressor response by a central action; perphenazine, prochlorperazine and atropine also reduced the vasopressor response but they did so by acting on the peripheral sympathetic outflow. Promazine and chlorpromazine reduced the medullary vasopressor response principally by a peripheral blocking action but there may be also a small central action component.

4. The importance of assessing the peripheral action of “centrally acting” drugs is emphasized.

5. The drugs benactyzine, hydroxyzine, mebutamate, chlorpromazine and promazine appear to exert a depressant action on the central sympathetic nervous system.