Comparative effects of various Rauwolfia alkaloids on centrally evoked vasopressor responses.

Certain Rauwolfia alkaloids (reserpine, rescinnamine,serpentine, ajmaline and ajmalicine) were investigated for their central vasodepressant effects in cats. 5-Hydroxytryptamine was included in this study because it has been implicated as a mediator in the action ofreserpine and rescinnamine. Pressor responses were elicited from the medullary vasopressor locus with the steriotaxic technic, and from the spinal cord by spinal fluid (CSF) compression after high spinalligation. Epinephrine (or norepinephrine) was used to determine peripheral drug effects on vascular reactivity. The results indicate that the alkaloids rescinnamine and reserpinine are to be classed with reserpine because of their mildly depressant effect on electrically induced medullary pressor responses and their lack of effect on pressor responses from spinal compression and from the injection of epinephrine. Similarly, the alkaloids serpentine and ajmaline can be classed with alseroxylon because of their primary depressant effect on pressor responses evoked by spinal compression as well as their potent depressant effect on medullary responses. These two alkaloids, like those in the reserpine group, did not appreciably affect pressor response to epinephrine. Ajmalicine has been demonstrated, by the cross-circulation technic, to possess central depressant activity in addition to its adrenergic blocking activity. 5-HT has been included in the reserpine group because of certain properties which serotonin shares with reserpine, including failure to produce spinal va omotor depression. Effects of the various alkaloids on the resting blood pressure level are complex and have been discussed in light of the central vaso-depressant influences of these drugs. The results of the investigation indicate that reserpine does not contribute significantly to the pronounced hypotensive activity of alseroxylon.