Various pharmacological agents affect cochlear blood flow in guinea pigs. Cochlear vessels appear to be weakly controlled by the adrenergic nervous system. Changes in systemic blood pressure easily overcome this control. Cholinergic agents (acetylcholine chloride, bethanechol chloride, pilocarpine hydrochloride dilate cochlear vessels although cochlea vasodilation does not necessarily cause cochlear blood flow increase because of associated systemic hypotension and bradycardia. Anticholinesterase agents (neostigmine methylsulfate, edrophonium chloride) produce small increases in cochlear blood flow, while cholinolytic agents (atropine sulfate, scopolamine hydrobromide) decrease and inhalation of carbon dioxide and amyl nitrite increase it. Papaverine hydrochloride, dipyridamole, bradykinin, kallidin, histamine phosphate, betahistine, hydralazine hydrochloride, and hypertonic solutions of glucose and sodium bicarbonate increase cochlear blood flow in spite of decreasing systemic blood pressure. Niacin and nicotinyl alcohol tartrate have no significant effect on cochlear blood flow.
James B. Snow, Fumiro Suga. Labyrinthine Vasodilators. Arch Otolaryngol. 1973;97(5):365–370. doi:10.1001/archotol.1973.00780010377001