The
multidrug resistance (MDR)
phenotype is associated with the expression of
P-glycoprotein (Pgp), coded by the multigenic mdr
family.
Mice present the
isoforms mdr1 and mdr3, which are responsible for
multidrug resistance, and mdr2, that is involved in the transport of
phospholipids. mdr1 expression has more recently been associated also with the
secretion of
steroid hormones. This
work presents an RT-PCR
analysis of the expression of mdr
isoforms, in several organs of
mice during different phases of the
estrous cycle. Additionally,
females were ovariectomized, submitted to different
hormone treatments, and their
uterus was analyzed for the expression of mdr
isoforms. The results show that in the
adrenal gland and
ovaries mdr1 is the main
isoform during
proestrus, and that
progesterone or a combination of
progesterone and
estrogen induce the expression of all mdr
isoforms in the
uterus of ovariectomized
females. We suggest that the functions of mdr1 and mdr3 are overlapping, that mdr3 may be the more efficient
isoform in the detoxification function, and that mdr1 may be more closely related to the
secretion of
steroid hormones.