Endogenous urea as an autacoid: extrarenal and renal focuses

The present position article complies with selected own and literature data concerning the characterization of endogenous urea at extrarenal level in animal and human organism in functional aspect. With key pharmacological experiments, both under in vivo and in vitro conditions, we apply urea in concentrations corresponding to physiological and pathological ones. We established that endogenous urea (without use as an exogenous applied drug) possesses important properties. It is assumed that urea is an endogenous non-specific beta-adrenergic receptor antagonist (ENBARA), non-selective, non-competitive, reversible and non-toxic. Based on these data we develop a concept for endogenous beta-adrenergic receptor antagonists (EBARA). In agreement with proofs of RJ Lefkowitz' group in the 90-ies that "beta arrestines 1 and 2 antagonize three of four agonist-activated beta-adrenergic receptors" we accept that they act as relatively endogenous specific beta-adrenergic receptor antagonists (RESBARA). As regards for the last four beta-agonist-activated adrenergic receptor we propose that is controlled via ENBARA. That is why a new role of urea is to be in the list of endocoids (autacoids).