TWO ACTIONS OF γ‐AMINOBUTYRIC ACID ON THE RESPONSES OF THE ISOLATED BASILAR ARTERY FROM THE RABBIT

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Abstract
1 In the isolated basilar artery of the rabbit, γ-aminobutyric acid (GABA) (ED50±s.e.mean, 2.4 ± 1.1 × 10−5 m) produced a relaxation, if the tone had been increased with 5-hydroxytryptamine (5-HT). 2 3-Aminoproprane sulphonic acid (3-APS) produced a similar, but smaller relaxation, while baclofen had no effect. The relaxation produced by GABA was inhibited by bicuculline. 3 Transmural electrical stimulation produced a reproducible contraction of the isolated basilar artery. In 9 out of 14 preparations GABA (ED50± s.e.mean, 5.6 ± 2.1 × 10−7 m) caused a reduction of the response, with a maximum of 49.2 ±4.3%. Bicuculline did not inhibit these responses to GABA. 4 Baclofen (ED50±s.e.mean, 6.8± 1.4 × 10−7 m) produced a similar inhibition (47.4±3.2% maximum) but 3-APS had no effect. 5 GABA (10−4 m) had no effect on the tone of isolated mesenteric or internal carotid arteries from the rabbit, whether or not the tone was increased with 5-HT. Similarly, GABA (10−4 m) did not produce any change in the responses to transmural stimulation in isolated mesenteric or internal carotid arteries. 6 These findings are consistent with the presence of two types of GABA receptor on the rabbit basilar artery.