Agonist concentration gradients as a generalizable regulatory implementation strategy

This article proposes a general mechanism by which biphasic dose-response r elationships occur in pharmacological and toxicological experimental system s. Such biphasic responses are mediated via a strategy of differential bind ing to stimulatory and inhibitory receptor subtypes based on agonist concen trations. Such a strategy is widely seen in pharmacological systems and has been demonstrated in toxicological-related biphasic dose responses in whic h the treatment altered levels of endogenous agonists.