Antagonism of inhibitory amino acids by the steroid derivative RU5135.

The steroid derivative RU5135 has been tested for its ability to antagonize glycine and the gamma-aminobutyric acid (GABA) analogue muscimol on isolated preparations of rat optic nerve and cuneate nucleus, respectively. On the cuneate nucleus, RU5135 antagonized muscimol in a competitive manner with a pA2 value of 8.31. RU5135 shared a common site of action with bicuculline that was separate from the picrotoxin site. On the optic nerve, RU5135 antagonized glycine with a pA2 of 7.67. It shared a common site of action with strychnine.