LM-2616

The compound LM-2616 (2,7,9-trimethyl-4 [N-methyl-piperazino] pyrido(3',2':4,5)thieno(3,2-d) pyrimidine, I) was found to inhibit isoprenaline-induced pos. chronotropic responses in atropinized and non-atropinized dogs.In guinea pig heart preparation, LM-2616 also inhibited isoprenaline-induced pos. chronotropic responses.Terbutaline, a specific beta₂-adrenoceptor agonist produced dose-dependent inotropic responses which were significantly antagonized by butoxamine.However, LM-2616 potentiated isoprenaline-induced pos. inotropic responses.In guinea pig tracheal chain and rat uterus, LM-2616, as well as terbutaline, produced dose-dependent relaxation.This effect was blocked by butoxamine in both the preparationsOn guinea pig tracheal chain it also potentiated isoprenaline-induced relaxation.LM-2616 was also found to exhibit local anesthetic activity.The LD₅₀ of the compound was found to be 480 mg/kg.Our data indicates that LM-2616 appears to be a specific beta₁-adrenoceptor antagonist with beta₂ adrenoceptor agonistic activity.