PHARMACOLOGICAL CHARACTERIZATION OF GABA RECEPTORS MEDIATING VASODILATION OF CEREBRAL-ARTERIES INVITRO

GABA produced a dose-dependent dilation of isolated cat and dog cerebral artery segments which were given an active, tonic contraction by either prostaglandin F2.alpha. or serotonin. No effect of GABA on extracranial blood vessels was observed. The GABA-induced dilation was blocked in a dose-dependent manner by bicuculline or picrotoxin. The latter agent appeared to act as a competitive antagonist. GABA agonists muscimol, imidazoleacetic acid, .delta.-amino-valeric acid, (.+-.).gamma.-amino-.beta.-hydroxybutyric acid and .beta.-alanine also relaxed actively contracted cerebral arteries dose-dependently. The relative potency of these agonists was consistent with that for GABA receptors on neurons and invertebrate striated muscle. GABA was tested on 2 human cerebral arteries and caused a small dilation. A cerebrovascular GABA receptor may mediate an interaction between GABA and the cerebral circulatory system.