[Action of repeated doses of a beta-adrenergic in the response of plasma cyclic AMP in asthmatic patients].

The present work studies the behaviour of plasma cAMP after repeated doses of a beta mimetic currently used as a broncodilator in asthmatics. A group of patients repeatedly treated with Phenoterol showed increased cAMP values, particularly evident when compared with those obtained throughout the day. It is notable that this increase does not continue with treatment, but levels off and even shows some tendency to diminish. After the final dose of beta mimetic there is an abrupt fall of cAMP to initial (pre-treatment) values. It is suggested that the increase in nucleotide values is not maintained after repeated doses of beta-stimulants because asthmatics show a diminished response as a result of exhaustion or "tolerance" to the response. It is probable that, as in the case of some hormones, the receptors in the effector organs are exhausted.