  We propose an evolutionary scenario by successive bursts of star formation to
reproduce the chemical properties of massive nearby Starburst Nucleus Galaxies
(SBNGs). The N/O abundance ratios in SBNGs are 0.2 dex higher than in normal
HII regions observed in the disks of late-type spirals. The variation of the
N/O ratio as a function of metallicity follows a "primary + secondary"
relation, but the increase of nitrogen does not appear as a continuous process.
Assuming that nitrogen is produced by intermediate-mass stars, we show that our
observations are consistent with a model where the bulk of nitrogen in SBNGs
was formed during past sequences of bursts of star formation which probably
started 2 or 3 Gyrs in the past.
