Nitric oxide synthase (NOS) in the human umbilical cord vessels. An immunohistochemical study

The placental-umbilical unit in sickle cell disease pregnancy: A model for studying in vivo functional adjustments to hypoxia in humans

The placental-umbilical unit in sickle cell disease (SCD) pregnancy was used to explore hypoxia in vivo, an important factor in the pathophysiology of this disease. Gross examination and microscopic analysis of the placentas, taken immediately after delivery, indicate good concordance between maturity and term as controls, but higher frequency of vascular injuries such as excess syncytial knots, excess fibrin deposits, congestion and villous necroses. Unexpectedly, neither leukocyte recruitment nor alteration in extraplacental membrane was observed, suggesting the absence of inflammation. Additionally, interleukin (IL)-6 and IL-8 concentrations, measured by enzyme-linked immunosorbent assay (ELISA), were similar in the placental maternal blood from controls and SCD. There were also no significant differences found in IL-6 vein blood concentrations between controls and SCD, IL-8 being not detected. Immunostaining of umbilical vein endothelium in SCD pregnancies showed redistribution of PECAM-1 (CD31), von Willebrand factor (vWF), and P-selectin to the cell surface, controls exhibiting the classical pattern. Staining quantification indicated increases in vWF (+36.2%; P=.006) and vascular endothelial growth factor (VEGF) expression (+96.0%; P=.006) over control, but a reduction in endothelial nitric oxide synthase (eNOS) (-45.5%; P=.029). These results document, for the first time, direct functional adjustments in response to hypoxia in human in vivo. The mechanism for these changes has not been clearly established, but it may reflect increased tolerance to SCD hypoxic conditions and hypoxia in general.

Preeclampsia is associated with loss of neuronal nitric oxide synthase expression in vascular smooth muscle cells of the human umbilical cord

AIMS

Umbilical blood vessels are not innervated and regulation of blood flow to the placenta must depend on structural changes and the effect of vasoactive factors. Failure to achieve these adaptations may result in reduced fetoplacental perfusion. The purpose of this study was to determine whether neuronal nitric oxide synthase (nNOS) is expressed in human vascular smooth muscle cells (VSMCs) of the fetoplacental circulation. nNOS has been described as a non-endothelial NOS counterregulating vasoconstriction only in the VSMCs of animal models. Therefore, we investigated nNOS expression in the fetoplacental unit from preeclamptic and healthy pregnancies.

METHODS AND RESULTS

We investigated nNOS regulation by immunohistochemistry, Western blotting and reverse transcriptase-polymerase chain reaction analysis. nNOS activity was determined by measuring the conversion of L-3H-arginine to L-3H-citrulline. nNOS expression was revealed only in VSMCs of the human umbilical veins, but not in umbilical arteries. A more direct assessment of nNOS activity showed that a small, but consistent amount of nNOS is present in the denuded media of the umbilical vein. In VSMCs of the umbilical veins during preeclampsia a total loss of nNOS protein expression and a significant decrease in mRNA expression were seen.

CONCLUSIONS

Loss of nNOS expression is associated with preeclampsia. It may alter the regulation of blood flow in the fetal and maternal placental vasculature in preeclampsia. However, the impact of NO produced by nNOS on the vascular tone of umbilical veins remains to be elucidated.

Umbilical cord morphologic characteristics and umbilical artery Doppler parameters in intrauterine growth-restricted fetuses

OBJECTIVE

To compare prenatal morphometric changes of umbilical cord components in intrauterine growth-restricted fetuses with and without abnormal umbilical artery Doppler parameters.

METHODS

Consecutive singleton intrauterine growth-restricted fetuses at a gestational age of older than 20 weeks were compared with matched appropriate-for-gestational-age fetuses. Intrauterine growth restriction was defined in the presence of a sonographic abdominal circumference below the 5th percentile for gestational age at the time of sonography and a birth weight below the 10th percentile. The sonographic examination included pulsed Doppler measurements of the umbilical artery resistance index and measurements of the umbilical cord cross-sectional area and the umbilical cord vessel area.

RESULTS

A total of 84 intrauterine growth-restricted fetuses and 168 appropriate-for-gestational-age fetuses were included in the study. All umbilical cord components (umbilical cord cross-sectional area, vein area, artery area, and Wharton jelly area) were smaller in the intrauterine growth-restricted fetuses. The prevalence of lean umbilical cords (cross-sectional area < 10th percentile for gestational age) was significantly higher in intrauterine growth-restricted fetuses compared with appropriate-for-gestational-age fetuses (73.8% versus 11.3%; P < .0001). A significant and progressive reduction of the umbilical vein area corresponding to the degree of umbilical artery Doppler parameter abnormality was found. The umbilical artery area was not related to the hemodynamic changes of the blood flow in the umbilical arteries.

CONCLUSIONS

The proportion of lean umbilical cords was higher in intrauterine growth-restricted fetuses than in appropriate-for-gestational-age fetuses. Umbilical vein caliber decreases significantly with worsening of umbilical artery Doppler parameters.

Localization of nitric oxide synthase type III in the internal thoracic and radial arteries and the great saphenous vein: a comparative immunohistochemical study

BACKGROUND

Endothelial nitric oxide synthase type III is the key enzyme of the nitric oxide production in the vessel wall. In this study the localization of endothelial nitric oxide synthase type III within the wall of the human internal thoracic and radial arteries and the great saphenous vein was investigated.

METHODS

Specimens were harvested from 23 patients undergoing surgical myocardial revascularization and submitted to light and electron microscope analysis using histochemical stainings and immunohistochemistry with specific antibodies anti-endothelial nitric oxide synthase type III, Factor VIII, and alpha-smooth muscle actin.

RESULTS

Endothelial nitric oxide synthase type III was evident in the intima of all conduits and, unexpectedly, in the muscle cells of the media of muscular internal thoracic arteries and radial arteries. No endothelial nitric oxide synthase type III expression was found in the media of great saphenous veins. Semiquantitative analysis revealed a higher endothelial nitric oxide synthase type III expression in the wall of internal thoracic artery, particularly at the level of the media.

CONCLUSION

Endothelial nitric oxide synthase type III is expressed in the intima of the internal thoracic and radial artery and the great saphenous vein and in the muscle cells of the media of the internal thoracic and radial arteries. However, the internal thoracic artery shows a higher intensity of endothelial nitric oxide synthase type III expression, particularly within the media. The present study provides the first demonstration of the endothelial nitric oxide synthase type III expression at the level of the smooth muscle cells of the tunica media of systemic human arteries and can provide an histologic explanation for the better results of the internal thoracic artery when used for coronary artery bypass grafting.

Haem oxygenase activity in human umbilical cord and rat vascular tissues

Carbon monoxide (CO) has been shown to affect vascular tone in smooth muscle cells and thus, may regulate regional or systemic blood pressure as well as fetoplacental vascular tone and fetal blood delivery. To assess the potential of vascular tissue to produce CO, we determined haem oxygenase (HO) activity through in vitro quantitation of CO production with gas chromatography and its inhibition by 33-66 microm of chromium mesoporphyrin (CrMP) in homogenate preparations of rat aorta and vena cava and human umbilical cord tissues. We compared these results to HO activity in rat heart and liver. We also discuss normalization of HO activity on a per mg protein as well as per g fresh weight (FW) tissue basis. We found that both rat vascular tissue HO activities (per g FW) were equal, but greater than that of heart (x3) and less than that of liver (x0.2). For human cord tissues, HO activities of artery and vein were equal, but greater than that of Wharton's jelly. Also, HO activity in rat vascular tissues was 3x greater than that of the human cord tissues. HO activity was completely inhibited by CrMP in rat heart (90 per cent) and liver (96 per cent), but incompletely (50-66 per cent) in both rat and human vascular tissues. We established that it is unlikely that other non-haem CO-generating processes account for this unique insensitivity of HO to CrMP inhibition. In fact, high concentrations of other potent metalloporphyrin inhibitors affected vascular tissue HO even less. We found that the degree of in vitro HO inhibition appeared to be related to the concentration of haem in the reaction medium. We conclude that the presence of HO activity in cord tissues supports the possibility that CO plays a role in fetoplacental blood flow regulation.

Ultrastructural localization of nitric oxide synthase and endothelin in the renal and mesenteric arteries of the golden hamster: differences during and after arousal from hibernation

This is a study of the electron-immunocytochemical localization of nitric oxide synthase (type III) and endothelin in renal and mesenteric artery endothelial cells of normal (active) and hibernating hamsters, as well as hamsters exposed to the cold but not hibernating, and hamsters aroused for 2h following hibernation. In the renal artery of hibernating hamsters and cold-exposed hamsters, a subpopulation of nitric oxide synthase-positive endothelial cells displayed immunoprecipitate predominantly in the vicinity of the Golgi complex indicating intracellular translocation from the cytoplasm to the Golgi complex. In hibernating animals, the percentages of both nitric oxide synthase-positive and endothelin-positive endothelial cells were notably lower than those observed either in active, cold-exposed or aroused animals. These changes may reflect a reduced endothelial contribution to the maintenance of vascular tone in these vessels during hibernation and an upregulation of expression of nitric oxide synthase and endothelin in the endothelium early on during arousal from hibernation.

Nonuniformity of endothelial constitutive nitric oxide synthase distribution in cardiac endothelium

Endocardial endothelium and endothelium of coronary vessels produce NO. Histochemical methods have suggested that coronary arterial endothelial cells contain more endothelial constitutive NO synthase (ecNOS) than does coronary venous endothelium. We have further investigated the distribution of ecNOS in cardiac endothelium using immunofluorescence and en face confocal microscopy of rat heart. In endocardial endothelium, confocal microscopy revealed distinct ecNOS labeling of peripheral cell borders, cytoplasmic labeling, and labeling of the Golgi complexes. Labeling of the cell borders and of the Golgi complexes was confirmed by double staining for ecNOS and for platelet and endothelial cell adhesion molecule or Golgi 58k protein, respectively. Cytoplasmic labeling was strongest in coronary arterial endothelium. The size of the ecNOS-labeled Golgi complexes decreased from coronary arterial endothelial cells (8.63 +/- 0.39 microm2, mean +/- SE of 5 rats) to endocardial endothelium (7.07 +/- 0.61 microm2) and to coronary venous endothelium (3.65 +/- 0.20 microm2). In addition, pixel intensity of ecNOS labeling was higher in arterial endothelial cells than in venous endothelial cells. Endothelium of myocardial capillaries also contained small ecNOS-labeled Golgi complexes. No correlation was observed between endothelial cell surface area and Golgi complex size. Caveolin-1 labeling was strongest in capillaries and did not coincide completely with ecNOS labeling in endocardial and venous endothelium. These results suggest that endocardial and coronary arterial endothelium in the rat have a higher synthetic activity and might express more ecNOS than is expressed by cardiac venous and capillary endothelium. The observed heterogeneity in ecNOS distribution might be related to the specific mechanochemical environment and function of each endothelial compartment.

Activation and dimerization of type III nitric oxide synthase by submicromolar concentrations of tetrahydrobiopterin in microsomal preparations from human primordial placenta

We have found in a previous study that 5-50 microM tetrahydrobiopterin (BH4) stimulated 1.2-2.5-fold Ca(2+)-dependent nitric-oxide synthase (NOS) activity in homogenates prepared from primordial human placentae. Now we report on the dramatic, about sixfold, activating effect of BH4 on this activity measured in microsomal preparations. Firstly, both in the absence and presence of BH4, arginine bound to kinetically homogeneous sites, with no significant change between the apparent KM values for arginine (3.12 +/- 1.99 microM and 2.06 +/- 1.13 microM in the absence and presence of 50 microM BH4 respectively, mean +/- s.d., n = 3). On the other hand, the Vmax values measured in different pools of placenta tissue varied between 2.5-7.55 (no BH4 added) and 13.3-58.5 (with BH4 added) pmol/min/mg protein. Secondly, the microsomal preparations responded sensitively to BH4 addition. A dose-response study indicated that as low as 79 nM final BH4 concentration stimulated NOS activity half-maximally, and 1 microM BH4 resulted in an almost maximal effect. Thirdly, immunoblot analysis combined with laser densitometric evaluation demonstrated that BH4 efficiently promoted the aggregation of microsomal NOS type III isozyme into a protein having the characteristics (electrophoretic mobility, resistance of SDS) of the dimeric form. Half-maximal dimerizing activity was reached at 148 +/- 33 nM BH4 (mean +/- s.d., n = 3), whereas 1 microM BH4 led to almost, maximal aggregation of monomers. This is the first time that BH4-induced dimerization of a NOS type III isoform has been demonstrated. Considering that human placenta predominantly expresses NOS type III isoform and BH4 concentration in this tissue is 207 +/- 87 nM, the present results strongly suggest that the dimerizing effect of BH4 is a crucial physiological mechanism for the assembly of active Ca(2+)-dependent NOS in the human primordial placenta.

Nitric oxide and human umbilical vessels: pharmacological and immunohistochemical studies

Human umbilical vessels are devoid of nerves and therefore endothelial cells may play an important role in the control of fetoplacental blood flow. In this study we examined the pharmacological effects of various substances, known to produce endothelial-mediated vasodilation in many blood vessels, on the human umbilical artery and vein from legal terminations [mean gestational age, 15 (8-17) weeks; n = 12] and normal term vaginal deliveries [mean gestational age, 39 (38-41) weeks; n = 12]. Acetylcholine, adenosine 5'-triphosphate, the calcium ionophore A23187 and substance P had no effect on raised vascular tone, whereas sodium nitroprusside relaxed 5-hydroxytryptamine (5-HT) preconstricted, umbilical artery and vein from both early and late pregnancy. L-NG-Nitroarginine methyl ester (L-NAME) had no effect on basal tone or on high tone, after it was raised by 5-HT. Localization of nitric oxide synthase [NOS, type I (neuronal)] was examined in the same umbilical vessels using electron immunocytochemistry. No NOS-immunoreactive endothelial cells were observed in the umbilical vessels taken during early pregnancy. However, the percentage of NOS-immunoreactive endothelial cells in umbilical artery and vein from late pregnancy was 3 and 10 per cent, respectively. These results suggest that nitric oxide contributes little, if any, to the local control of umbilical blood flow throughout pregnancy, despite the presence of NOS-immunoreactivity in a subpopulation of endothelial cells in late pregnancy.