Apparent pA2 estimation of benzodiazepine receptor antagonists

The in vivo equivalent pA2 values for benzodiazepine (BZ) antagonists Ro15-1788 and CGS 8216 were estimated using diazepam as agonist. ED50 value of diazepam was established against pentylenetetrazole-induced seizures in rats. This value was raised by pretreatment with BZ antagonists Ro15-1788 and CGS 8216, in a dose-dependent manner. The apparent pA2 values for Ro15-1788-diazepam pair and CGS 8216-diazepam pair were found to be 5.28 and 5.48, respectively, which indicates almost equal antagonistic potency at the BZ receptor in reversing the protective effect of diazepam against pentylenetetrazole seizures in rats.