Abstract
1. 1. Some new pharmacological activities of bicuculline were found in isolated rat atria, mouse vas deferens and guinea-pig ileum. 2. 2. In isolated rat atria bicuculline (10–300 μM) induced potent positive inotropic and negative chronotropic effects which were not antagonized by propranolol (1 μM), 6-hydroxydopamine pretreatment (50 mg/kg i.v. twice), ranitidine (3 μM) or atropine (1 μM). Bicuculline (10–300 μM) potentiated electrically evoked contractions in mouse vas deferens and inhibited them (30–500 μM) in guinea-pig ileum. It was inactive on unstimulated mouse vas deferens. 3. 3. The above effects were completely reproduced by the bicuculline related-substance, β-hydrastine, but not by the bicuculline N-methyl derivative, bicuculline methiodide (BMI), on the isolated rat atria. BMI inhibited instead of potentiating the mouse vas deferens twitches and potentiated instead of inhibiting the guinea-pig ileum twitches. 4. 4. Picrotoxin, the other classic non-competitive GABA A antagonist, was completely devoid of the effects reported for bicuculline. 5. 5. We concluded that, on the three preparations studied, bicuculline possesses some effects which are unrelated to its GABA A receptor blocking activity.
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