Studies of the new hypotensive drug ST 155.

Abstract

Abstract G.A. BENTLEY and D.M.F. LI, Studies of the new hypotensive drug ST 155, European J. Pharmacol. 4 (1968) 124–134. The hypotensive drug ST 155 has been studied in isolated organs in pithed rats, and in anaesthetised rats and cats in an attempt to elucidate its mode of action. Though it has weak ganglion-blocking actions in some situations, it is unlikely that this contributes to its hypotensive effect. Similarly, its weak ability to depress the response to noradrenaline in isolated vas deferens and artery preparations seems inadequate to explain its hypotensive action, especially as it potentiates the pressor response to noradrenaline in intact and pithed animals. A depressant action of ST 155 on the vasomotor centre appears to be the most likely mode of action of the drug, since hypotension does not occur in pithed rats. Furthermore the pressor response to physostigmine is blocked by ST 155 in this species. A species difference was noted in that ST 155 potentiated the carotid occlusion reflex in the rat, but depressed it in the cat. This, plus the finding that after denervation of the carotid sinuses in cats, the hypotensive action of the drug reaches a maximum very rapidly, but returns to control level much sooner than in intact animals may indicate some action in sensitising the afferent arm of the baroreceptor mechanism.