  In-medium effects on transverse-mass distributions of quarks and gluons are
considered assuming a possible local equilibrium for colorless quark objects
(mesons and baryons) created in central A-A collisions. It is shown that the
average transverse momentum squared for these partons grows and then saturates
when the initial energy increases. Within the quark-gluon string model it leads
to the colliding energy dependence of hadron transverse mass spectra which is
similar to that observed in heavy ion collisions. Comparison with other
scenarios is given.
