EFFECTS OF RAUWOLFIA ALKALOIDS ON HYPOTHALAMIC, MEDULLARY AND SPINAL VASOREGULATORY SYSTEMS

¹ Department of Pharmacology, University of Utah School of Medicine, Salt Lake City, Utah

The effects of the Rauwolfia preparations, alseroxylon and reserpine, on vasoregulatory mechanisms were studied in vagotomized cats maintained on artificial ventilation. No evidence could be obtained for any local activating effect of Rauwolfia on afferent receptor sites, stimulation of which causes hypotension, since carotid sinus denervation, with or without nodose ganglionectomy, during the peak effect of the drug, did not result in neurogenic hypertension. Rapid i.v. injection of alseroxylon produced an immediate and transient fall in blood pressure attributable to a peripheral (cardiac or vascular) action, as concluded from experiments on spinal preparations. Studies on the differential effects of Rauwolfla alkaloids on hypothalamic, medullary and spinal vasomotor activity were performed. The stereotaxic technic was utilized to determine supraspinal electrical excitability; elevation of cerebrospinal fluid pressure was used to evoke pressor responses from the spinal animal. Alseroxylon was found to have a depressant action at the spinal as well as the medullary and hypothalamic levels. Reserpine, on the other hand, did not exhibit a significant spinal component of action but exerted a definite depressant effect, though of moderate degree, on supraspinal mechanisms. Hypotension and depression of vasomotor reflex excitability by the Rauwolfia preparations could be demonstrated even following midcollicular decerebration; the hypothalamus was thus excluded. Vaso-inhibitory responses to electrical stimulation of the medulla were more readily depressed by the drugs than were pressor responses to either medullary stimulation or carotid occlusion.

The physiological implications of these findings are discussed in the light of recently proposed hypotheses concerning the locus of the hypotensive action of Rauwolfia.