  The production of prompt photons at high energies provides a direct probe of
the dynamics of the strong interactions. In particular, one expect that it
could be used to constrain the behavior of the nuclear gluon distribution in
$pA$ and $AA$ collisions. In this letter we investigate the influence of
nuclear effects in the production of prompt photons and estimate the transverse
momentum dependence of the nuclear ratios $R_{pA} = {\frac{d\sigma (pA)}{dy d^2
p_T}} / A {\frac{d\sigma (pp)}{dy d^2 p_T}}$ and $R_{AA} = {\frac{d\sigma
(AA)}{dy d^2 p_T}} / A^2 {\frac{d\sigma (pp)}{dy d^2 p_T}}$ at RHIC and LHC
energies. We demonstrate that the study of these observables can be useful to
determine the magnitude of the shadowing and antishadowing effects in the
nuclear gluon distribution.
