  It has been known since many decades that galaxy interactions can induce star
formation (hereafter SF) enhancements and that one of the driving mechanisms of
this enhancement is related to gas inflows into the central galaxy regions,
induced by asymmetries in the stellar component, like bars. In the last years
many evidences have been accumulating, showing that interacting pairs have
central gas-phase metallicities lower than those of field galaxies, by {\sim}
0.2-0.3 dex on average. These diluted ISM metallicities have been explained as
the result of inflows of metal-poor gas from the outer disk to the galaxy
central regions. A number of questions arises: What's the timing and the
duration of this dilution? How and when does the SF induced by the gas inflow
enrich the circumnuclear gas with re-processed material? Is there any
correlation between the timing and strength of the dilution and the timing and
intensity of the SF? By means of Tree-SPH simulations of galaxy major
interactions, we have studied the effect that gas inflows have on the ISM
dilution, and the effect that the induced SF has, subsequently, in re-enriching
the nuclear gas. In this contribution, we present the main results of this
study.
