Cholinergic-like effects of hypertonic solutions

Abstract

A consideration of the physiological effects of hypertonic solutions suggested that certain aspects might be cholinergic. This hypothesis has been investigated. Concentrated urea, glucose or salt solutions were rapidly injected intravenously into 25 anesthetized dogs. Systemic and pulmonary vascular pressures were monitored and compared with those obtained with acetylcholine. Data were collected before and after cervical vagotomy or treatment with physostigmine or atropine. The effects of hyperosmotic media and acetylcholine were similar. Both, in lower concentrations, produced transitory vasodilatation; bradycardia and cardiac irregularities became superimposed with stronger solutions. However, the hypertonic phenomena were ameliorated by vagotomy, unaffected by atropine and only partially potentiated by Eserine. Vasodilatation required a latent period of about 10 seconds beyond the circulation time. The evidence suggests that hypertonic materials evoke release of acetylcholine as a result of reflex and central nervous excitation. In addition, they exert a direct cholinergic-like action, mediated possibly through depolarization of cholinergically innervated effector cells from osmotic dehydration.