  The effect of mixing of the vector and axial vector correlation functions in
the nuclear medium arising from the interaction of nuclear pions with
corresponding interpolating currents is considered. It is shown that the mass
difference between $\rho$ and $a_1$ meson gets smaller with the increase of the
nuclear density reflecting the phenomena of partial restoration of chiral
symmetry whereas the absolute values of meson masses may both decrease and
increase in nuclear medium depending on the model used for the phenomenological
spectral density.
