Pre-junctional alpha 2-adrenoceptor activity of B-HT920.

An in-vitro study has been carried out on the pre-junctional alpha 2-adrenoceptor activity of the thiazoloazepine derivative B-HT 920 (6-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]-azepine) using field-stimulated rat vas deferens and guinea-pig ileum. The alpha 2-selective agonists clonidine (an imidazoline derivative) and alpha-methyl noradrenaline (a beta-phenethylamine derivative) were compared. Results show that B-HT 920 is a potent agonist on pre-junctional alpha 2-adrenoceptors and is competitively antagonized by the selective alpha 2-adrenoceptor antagonist yohimbine. The characteristics of the pharmacological responses obtained with B-HT920 indicate that it interacts with the receptor in an imidazoline-like, rather than a beta-phenethylamine-like, manner.