  According to recent analyses of the type-Ia supernova rate as a function of
redshift, delayed and prompt type-Ia supernovae (SN Ia) should explode
respectively in the Galactic bulge and in the nuclear bulge, a gas rich
structure with ongoing star formation, located in the central region of the
Milky Way. We estimate the rate of type-Ia supernovae in the Galactic bulge and
nuclear bulge. We show that this rate is insufficient by an order of magnitude
to explain by positron escape from type-Ia supernovae envelopes alone the large
positron injection rate into the Galactic central region, as re-observed
recently by the Spectrometer on INTEGRAL, which amounts to 1.25 10^{43} e+
s^{-1} and would require 0.5 SN Ia explosions per century.
