The nature of the stimulatory action of ?-aminobutyric acid in the isolated perfused dog adrenals

Abstract

The effect of γ-aminobutyric acid (GABA) on catecholamine (CA) release from adrenal medulla was investigated. GABA and GABA agonists, 3-amino-1-propanesulfonic acid and imidazole-4-acetic acid caused CA release from isolated perfused dog adrenals in a dose-dependent manner, and no tachyphylaxis to GABA was observed. CA release elicited by GABA was antagonized by bicuculline and picrotoxin. This antagonism was specific for GABA-and GABA agonist-induced responses, response to acetylcholine being unaffected. Pretreatment with atropine plus hexamethonium did not affect the response to GABA. GABA-induced CA release was abolished by the removal of Ca²⁺ from perfusion medium, but not by the removal of Na⁺ or Cl⁻. Verapamil, CoCl₂ and dibucaine blocked the effect of GABA. A Na⁺ channel blocker, tetrodotoxin did not reduce GABA-evoked CA release. These results suggest that GABA may interact with its receptor to evoke CA release from adrenal medulla in a fashion of Ca²⁺-dependence and independence on external Na⁺ or Cl⁻.