Loss of endothelial cell BH4 during pregnancy caused
vascular dysfunction uterine arteries from pregnant
Gch1fl/flTie2cre mice.
We next determine how loss of endothelial cell Gch1 impacts on
pregnancy induced vascular adaptations of the uterine artery. Firstly,
the lumen diameter of uterine arteries, as determined by the
length-tension relationship, was significantly increased in pregnancy in
both genotypes with no difference between genotypes observed in either
pregnancy or non-pregnancy mice (Pregnant WT: 258 ± 12.6 μm, PregnantGch1fl/fl Tie2cre: 276 ± 12.7 μm; Nonpregnant WT
155 ± 6.6 μm, nonpregnant Gch1fl/fl Tie2cre: 153
± 3.1; P<0.05 ) (Figure 2A). This was accompanied by a
greater KCl response (~2-fold increased) in uterine
arteries from pregnant wild-type andGch1fl/fl Tie2cre mice (Pregnant WT: 5.8 ± 0.7
mN, Pregnant Gch1fl/fl Tie2cre: 5.1 ± 0.4 mN,
nonpregnant WT: 2.6 ± 0.3 mN, nonpregnantGch1fl/fl Tie2cre: 2.3 ± 0.4;P<0.05 ) (Figure 2A), indicating that a normal pregnancy
is associated with increased lumen size and media thickness of the
uterine artery. However, loss of endothelial cell Gch1 in
pregnancy lead to an increase in uterine artery stiffness, with
increased wall tension in response to increasing stretch observed in
uterine arteries from pregnancyGch1fl/fl Tie2cre mice compared with wild type
controls (Supplementary Figure 1).
In contrast to the aorta, uterine arteries from pregnant wild type mice
had a significantly attenuated contractile response, with a
corresponding increase in the EC50 and decrease in Emax
(% maximum contraction) to the TxA2 receptor against, U46619, (Figure
2B, C, and D). Incubation with the NOS inhibitor L-NAME lead to a
significant augmentation of the contractile response (Figure 3E),
indicating that the pregnancy induced attenuation was due in part to
increased NOS-derived NO.
However, uterine arteries from pregnantGch1fl/fl Tie2cre mice showed incomplete
adaptation to pregnancy with a significantly greater contractile
response observed compared with arteries from pregnant wild type mice,
as demonstrated by an increased maximum constriction and reduced
EC50 (Figure 2B, C, and D). This difference appeared to
be driven in part by a reduced NOS dependent production of vasodilators
in uterine arteries from pregnantGch1fl/fl Tie2cre mice as in contrast to wild
type mice. L-NAME did not alter the vasoconstrictor response in uterine
arteries from pregnant Gch1fl/fl Tie2cre mice
(Figure 2E).
In wild-type uterine arteries, endothelium-dependent vasodilatation to
ACh was significantly enhanced in pregnancy compared to nonpregnant
wild-type controls (Figure 2F; P<0.05 ). This was
accompanied by a significantly enhanced endothelium-independent
vasodilatation in response to nitric oxide donor, sodium nitroprusside
(SNP), indicating increased vascular smooth muscle sensitivity to
downstream NO signalling pathway during pregnancy (Figure 2I).
In contrast, pregnancy induced enhanced endothelium-dependent
vasodilatations was blunted in pregnantGch1fl/fl Tie2cre uterine arteries with no
difference in endothelial cell mediated dilation between pregnancy and
non-pregnant uterine arteries from knock out mice (Figure 2F, G and H).
This blunted pregnancy induced vascular remodelling was observed despite
the presence of pregnancy induced enhanced endothelium-independent
vasodilatation in response to nitric oxide donor, SNP (Figure 2I).