  Different representations of an effective, covariant theory of the hadronic
interaction are examined. For this purpose we have introduced nucleon-meson
vertices parametrized in terms of scalar combinations of hadronic fields,
extending the conceptual frame of the Density Dependent Hadronic Field Theory.
Nuclear matter properties at zero temperature are examined in the Mean Field
Approximation, including the equation of state, the Landau parameters, and
collective modes. The treatment of isospin channels in terms of QCD sum rules
inputs is outlined.
