[en] A study is made in ¹⁶O and infinite nuclear matter of the effects of mesonic and isobar degrees of freedom and the effect of the eikonal form factor in the meson-nucleon vertex of the nucleon-nucleon interaction. Three main effects are seen: First, the mesonic degrees of freedom are found to play a significant role by introducing additional density dependence, which results in a large improvement of the radius with a small change in the energy for ¹⁶O. Second, when the isobar and mesonic degrees of freedom are combined, repulsion is obtained in ¹⁶O with a corresponding increase of the radius. These results are relatively insensitive to the replacement of part of the pionic form factors by the rho meson in the transition potentials to intermediate states with Δ resonances. Third, the use of the eikonal form factor, instead of phenomenological ones of the dipole type, results in additional attraction. This effect persists when the eikonal form factor is used in a potetial that includes mesonic degrees of freedom