Deficiency in endothelial cell Gch1/BH4 during pregnancy
leads to impaired vascular function in aortas from pregnant
Gch1fl/flTie2cre mice.
First, we determined the physiological requirement for endothelial
cell-specific Gch1 /BH4 biosynthesis in vasomotor function in
conduit arteries from both nonpregnant and pregnantGch1fl/fl Tie2cre and wild-type mice using wire
myography. Isometric tension studies in isolated aortas demonstrated no
difference in vasoconstriction responses, expressed as percentage
contraction to KCl, prior to pregnancy between the genotypes (Figure 1B
and C). However, at late stage of pregnancy loss of endothelial cellGch1 lead to a significant increase in vasoconstriction to
phenylephrine (Figure 1B and C). This difference was unlikely due to
structural difference between genotypes in pregnant mice as constrictive
responses to KCl were similar across all groups (nonpregnant WT: 4.68 ±
0.41mN, vs. nonpregnant Gch1fl/fl Tie2cre: 5.13
± 0.32mN, Pregnant WT: 4.35 ± 0.19mN, vs. PregnantGch1fl/fl Tie2cre: 4.74 ± 0.19,P<0.05 ; Figure 1D). The difference between genotypes
was normalized in the presence of L-NAME (Figure 1E), indicating that
the increased constrictor response in pregnantGch1fl/fl Tie2cre aortas is likely mediated by
tonic eNOS-mediated vasodilatation.
There was no difference in endothelium dependent vasodilatation to
acetylcholine between the genotypes prior to pregnancy. However, in late
stage of pregnancy, endothelium-dependent vasodilatation to
acetylcholine was significantly impaired in pregnantGch1fl/fl Tie2cre aortas when compared with
aortas from pregnant wild-type mice and aortas from non-pregnantGch1fl/fl Tie2cre mice (Figure 1F and G). In the
presence of L-NAME, endothelium-dependent vasodilatation to
acetylcholine in pregnant and nonpregnant mice of both genotypes was
totally abolished (Figure 1H), indicating that eNOS is the major source
of vasodilators in mouse aortas in both pregnant and non-pregnant mice.
Interestingly, we found that pregnancy significantly increased the
potency of endothelium-independent vasodilatation to the nitric oxide
donor, sodium nitroprusside (SNP) in aortas from both wild-type andGch1fl/fl Tie2cre mice when compared to aortas
from nonpregnant wild-type mice (Figure 1I), suggesting that a normal
pregnancy is associated with an increased sensitivity to nitric oxide
downstream signalling pathway in conduit arteries.