Cerebrovascular effects of ammonia in vitro.

The effect of ammonia (ammonium salts) upon human and rabbit cerebral arteries was studied in vitro. Ammonia (NH3/NH4+) caused relaxation of cerebrovascular smooth muscle which was transient and occurred irrespective of how the vessels were preconstricted (potassium-Krebs solution, noradrenaline, serotonin, prostaglandin F2 alpha). The effect was independent of ammonia-induced extracellular changes in pH. It is concluded that ammonia may contribute to the vasodilatation and increase in cerebral blood flow which occurs under certain pathophysiological conditions.