Abstract
Imipramine, a potent antidepressant, has been reported to cause hypotension in cats when administered intravenously. The fall in blood pressure due to high doses of imipramine has been attributed to adrenergic blocking action of the drug (1). Lower doses of imipramine (320 μg/kg i.v.) also cause hypotension although at this dose level it does not produce adrenergic blockade. The cause of hypotension due to low doses of imipramine has still not been explored and the reported observations do not provide any explanation for this response. The ganglion blocking and the adrenergic neurone blocking action of imipramine has been ruled out by the observations of Osborne and Sigg (1). Furthermore, they have ruled out acetylcholine like action of imipramine. The direct vasodilator effect of this drug has been excluded (2). These reports exclude the possibility of action of small dose of imipramine on the efferent limb of the reflex arc regulating blood pressure. It was, therefore, thought desirable to study the effect of imipramine on the medullary and spinal vasomotor loci.
