 Abstract | Hypertension, is a common clinical complication of pregnancy, often leading to preeclampsia
and fetal intrauterine growth retardation. Many studies have shown that
vascular endothelial growth factor A (VEGF-A) is a potent angiogenic factor, that is, it
is responsible for the formation of new blood vessels from existing vessels. VEGF-A
has been shown to be expressed in uteroplacental tissues, particularly during
implantation. Levels of VEGF-A mRNA have also been shown to be significantly
lower in placental tissue from pre-eclamptic women compared with control women
(Cooper et al, 1996). The first aim of this project, was to establish the use of RT-PCR
(reverse transcriptase-polymerase chain reaction), Northern blot analysis,
immunohistochemistry and in situ hybridization, to measure the expression and
localization of VEGF-A, vascular endothelial growth factor receptor 1 (VEGFR-1)
and vascular endothelial growth factor receptor 2 (VEGFR-2) in normal rat
uteroplacental tissues at early, mid and late gestation. The second aim of this project
was to measure expression of VEGF-A, VEGFR-1 and VEGFR-2 in uteroplacental
tissues of the normotensive (WKY) and the spontaneously hypertensive rat (SHR) at
7, 11 and 19 days of gestation. Spontaneously hypertensive rats have been previously
established as an animal model for pre-eclampsia.
The uterus containing the placenta and fetus was removed from normal Sprague
Dawley, WKY and SHR rats over a range of gestational ages. After 11 days of
gestation, the uterus and placenta were separated. Tissues were frozen immediately in
liquid nitrogen and stored at -80oC, or fixed in 10% formaldehyde for
immunohistochemistry. Total RNA was extracted using TRIZOL reagent and mRNA
levels of VEGF-A and its receptors were examined using RT-PCR and Northern blot
analysis. mRNA levels of VEGF-A and its receptors were compared with those of the
housekeeping gene glyceraldehyde 3-phosphate dehydrogenase (G3PDH).
We have successfully used RT-PCR to measure mRNA expression of VEGF-A,
VEGFR-1 and VEGFR-2; Northern blot analysis to measure expression of VEGF-A,
and immunohistochemistry to localize VEGF-A protein in rat uteroplacental tissues.
We have shown that VEGF-A and its receptors were expressed in uteroplacental
tissues of the normal rat. We found no major differences in the expression levels of
VEGF-A and VEGFR-1 in uteroplacental tissues at early, mid and late gestation. We
showed that VEGF-A164 was the predominant isoform found in uteroplacental tissues.
Finally, we found no major differences in the expression levels of VEGF-A, VEGFR-1
and VEGFR-2 in uteroplacental tissues in normotensive rats (WKY) compared with
hypertensive rats (SHR).
We conclude that VEGF-A and its receptors, VEGFR-1 and VEGFR-2, were
expressed in uteroplacental tissues of pregnant rats. Furthermore, mRNA levels of
VEGF-A and its receptors were comparable in normotensive and hypertensive rats.
These results suggest that VEGF-A and its receptors may have an important role in the
development of the fetal and maternal portions of the placenta, but that they are not the
primary factors involved in the aetiology of pre-eclampsia. |
