I. v. or i.a. injection of GABA produced a transient apnoea in rats under pentobarbital anaesthesia. The dose-response relationship and specifity of this effect were investigated. 2. Injection of GABA into the femoral vein led to an apnoea of dose-dependent duration, the dose-response curve showed an ED50 of about 5 mumoles GABA kg-1 and a maximum duration of about 8 s. 3. The depressant action of systemic GABA on respiration seems to be specific as only close structural analogues of GABA such as trans-4-aminocrotonic acid, beta-hydroxy-GABA, delta aminovaleric acid, beta-alanine, and taurine were able to mimic the action of GABA. 4. Injection of these structural analogues of GABA 15 s rior to an injection of GABA inhibited the respiratory depressant effect of GABA dose-dependently. Picrotoxin also antagonized the apnoic action of GABA. 5. The results indicate that the apnoea induced by systemic injection of GABA is mediated by an action on GABA receptors.
