Indirectly acting agonists. A model for the functional interaction of released endogenous double agonists

A theoretical model is presented to describe the functional interaction of an endogenous double agonist released by an indirectly acting agonist. The model takes into account the functional interaction of a released double (dualistic) agonist and describes both functional synergism and antagonism. It was shown that receptor density plays an important role in determining the profiles of concentration-effect curves and that it is necessary that the model should incorporate a parameter which describes receptor density. The model predicted that the shape of the concentration-effect curves may be sigmoid or bell-shaped. The theoretical predictions are comparable with experimental results.