抄録
1.The effects ofγ-aminobutyric acid (GABA) on the isolated guinea pig ileum were investigated.
2. In the absence of other drugs GABA produces occasionally stimulation and also relaxation, which are abolished by atropine (1μg/ml.), LSD (0.01μg/ml.) and picrotoxin (10μg/ml.).
3. Effects of GABA on the dose-response curves of gut-stimulating drugs were examined and found that it has an antagonistic action to acetylcholine, nicotine and 5 HT, the anti-5 HT action being the highest and the anti-Ach one the lowest. But hardly any antagonism between GABA and histamine or BaCl2 is observed.
4. The anti-5 HT and anti-nicotine actions of GABA are abolished or more or less depressed by LSD (0.0005μg/ml.), dibenzyline (0.001-0.1μg/ml.), atropine (1μg/ml.), and picrotoxin (10μg/ml.), but scarcely affected by pyribenzamine (10μg/ml.) and strychnine (100μg/ml.). The anti-nicotine action are also blocked by desensitization for 5 HT due to application of its high dose, while the anti-5 HT action is hardly influenced by high dose of hexamethonium (10-100μg/ml.) which is a sufficient dose to block the gut-stimulating action of nicotine.
5. The peristalsis of isolated guinea pig ileum, recorded by means of the method similar to that of Bülbring and Lin, is also blocked or depressed by 1-100 μg/ml. GABA, when applied outside, but barely affected by its inside application. This action was found to be blocked by LSD, dibenamine and picrotoxin. The peristalsis-inhibiting action of 5 HT is also blocked by LSD and dibenamine in their appropriate concentrations of not affecting the peristalsis, but picrotoxin has no such effect. When applied inside, GABA also depresses the peristalsis-promoting action of 5 HT applied inside.
6. Based on the results stated above and those obtained on the stretch receptors of crayfish or on the frog spinal reflex, it is suggested that the sites of action of GABA would have a close correlation with the tryptamine receptors.
