## 4 Discussion
### VDR Protein Level in Placentas  
Second interesting observation was the lower VDR protein level (\(p\) < 0.001) in placentas of preeclampsia women. Numerous studies have assessed the protein level of VDR and hydrolases involved in the VD pathway in placenta from preeclampsia women. Our obtained results are consistent with several previous analyses performed in women with preeclampsia and fetal growth restriction (FGR). In the study by [PERSON] et al., the VDRprotein level in placenta was reduced in FGR pregnancies compared to the healthy control group [46].  
Moreover, in our research was to find in the whole studied group a positive correlation between placental VDR protein level and gestational age (\(p<0.001\)) as well as infant birth weight (\(p=0.014\)). This issue has been discussed in several aspects in recent analysis.  
It is also noteworthy that in our whole study group the VDR protein level in placentas was inversely correlated with systolic and diastolic blood pressures (all \(p<0.001\)). In animal studies it was proposed that vitamin D serum level is involved in the pathogenesis of cardiovascular diseases as well as arterial hypertension. In correlation with the blood pressure level, vitamin D shows antihypertensive properties through reducing renin-angiotensin-aldosterone system activity and improves vasodilation [49; 50]. Following this information it is believed that the best antihypertensive vitamin D effect is noted in patients with elevated blood pressure and, additionally, VD deficiency [51; 52].  
[PERSON] et al. in an animal model noted reduced blood pressure after VD supplementation during pregnancy. In addition, the authors observed improvement of placental angiogenesis by normalizing the VEGF and Flt-1 placental levels, without influencing the levels of PfGF and Hifl\(\alpha\)[53].  
Despite these observations, the human clinical research reveals inconsistent results in this field. [PERSON] et al. observed a significantly lower VD level in the PE group compared to healthy normotensive women (\(p<0.001\)), as well as a negative correlation of VD level with systolic (\(p<0.001\)) and diastolic blood pressure (\(p<0.001\)) [54]. [PERSON] et al. reported that low VD level could be a risk factor for early- and late-onset PE occurrence [55]. Interestingly, [PERSON] et al. did not detect any effect of VD intake on maternal blood pressure in healthy pregnant women [56].  
[PERSON] et al. reported that VD deficiency disturbed homeostasis of the inflammatory response in the placenta, activating the cytokine network and followed by spontaneous premature preterm delivery [57]. At the same time, [PERSON] et al. observed a correlation between maternal VD levels and VDR gene polymorphisms, as well as the risk of premature birth [58]. No less interesting was the observation that maternal VD serum level was associated with infant birthweight among both white and black women [59; 60].  
Because the VD metabolism is closely linked with VDR protein activity, it is clear that placental VDR gene and protein expression could play a significant role in regulation of blood pressure in healthy pregnant as well as preeclampsia women [61; 62] and have a significant impact on preterm birth occurrence and newborn birthweight.