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.