Studies using KWD 2058, a derivative of terbutaline in isolated atrial and tracheal preparations from the guinea-pig.

KWD 2058 is a derivative of terbutaline in which the ring hydroxy groups are esterified with isobutyric acid. In guinea-pig atrial and tracheal preparations KWD 2058 produced slowly developing beta-receptor mediated actions which were absent in preparations pretreated with physostigmine. Incubation of KWD 2058 with guinea-pig plasma resulted in the production of a compound which was indistinguishable from terbutaline on both a qualitative and quantitative basis. KWD 2058 produced negative inotropic and chronotropic actions and increased the effective refractory period of guinea-pig atria. In addition, KWD 2058 produced a non-competitive antagonism of chronotropic responses to (--)-isoprenaline in atria. It is concluded that KWD 2058 has no affinity for beta-adrenoreceptors and that any beta-agonistic activity displayed is due to its hydrolysis product, terbutaline.