Effect of urea, glycerol, and mannitol on basilar and labyrinthine arteries.

We studied the effect of urea, glycerol, and mannitol on basilar and labyrinthine arteries of dogs in vitro by use of tension recording methods. When the tissue was exposed to urea or glycerol, temporary relaxation of smooth muscles was initially observed, but was followed by gradually increasing contraction. With mannitol, relaxation of the smooth muscles remained stable as long as mannitol existed in the bathing solution. When the specimens were washed with normal Krebs solution after exposure to any of these three substances, large phasic contractions of the smooth muscles were observed. While only theoretical, we propose a possible explanation for the different effects of these three drugs in the improvement of hearing loss that results from Meniere's disease.