On the mechanisms of hypotensive action of indoramin.

Effect of indoramin in small doses on the central vasomotor loci has been studied in chloralose anesthetized cats by localizing it to the central sites. An intracerebroventricular dose of 100 micrograms or intra-vertebral arterial injection of 50 micrograms significantly inhibited the excitability of hypothalamic and medullary vasomotor loci and produced hypotension. Similarly, topical application of indoramin (0.5%) to the floor of the IV ventricle inhibited the medullary and the hypothalamic vasomotor responses but a similar application to the ventral surface of the medulla had no effect. An intrathecal dose of 100 micrograms did not inhibit the spinal compression vasmotor response. Administration of higher amounts led to inhibition of the adrenaline pressor response also, indicating a peripheral leak of the drug. Indoramin has a definite inhibitory effect on the medullary vasomotor loci which contributes to the hypotension produced by this drug.