Revistă de Medicină şi Farmacie - Clujul Medical - Iuliu Haţieganu

336
Patologie ginecologică
produced within the neighboring endothelial cells. Among
these mediators, prostaglandins have been shown to be
produced within the umbilical vascular endothelium [11].
Some authors observed similar defective prostacyclin
production of umbilical arterial response in cords delivered
to cigarette smoking mothers.
Another vasodilator that has attracted much attention
is nitric-oxide identical with the endothelium-derived
relaxing factor, which is produced from the conversion
of L-arginine to citrulline by nitric oxide synthase (NOS).
This enzyme has been detected immunohistochemically not
only in villous syncytiotrophoblast, but also in fetal villous
and umbilical endothelium. A reduction in this enzyme’s
activity has been correlated with abnormal umbilical artery
waveforms [12].
Atrial natriuretic peptide (ANP) is another potent
vasodilator that additionally seems to be involved in fetal
fluid hemostasis. Its binding sites have been detected in
umbilical smooth muscle cells. Immunoreactivity for the
peptide itself and its messenger RNA have been found in
the umbilical endothelium.
Vasoconstrictor substances found in umbilical
endothelium comprise angiotensin II, 5-hydroxytryptamine
(5-HT) and thromboxane, neuropeptide Y (NPY), as well
as endothelin-1. Bindings sites for endothelin-1 have been
described in the media of umbilical vessels, the activity of
the arteries exceeding that of the vein. The functions of
these vasoconstrictors are still under discussion [13].
Immature vessels were more sensitive to angiotensin
II, arachidonic acid, and oxytocin; term vessels reacted
more to vasopressin, norepinephrine, PGD 2
, and PGE 2
.
These findings shed new light on the highly
complex mechanisms of autoregulation, not only of the
umbilical circulation, but also of the villous circulation, as
most of these mediators have been described also in the
walls of the larger chorionic and villous vessels. Further
studies will have to elucidate the complicated interactions
of these substances, as they are very likely to be involved
in abnormal conditions, such as intrauterine growth restriction
(IUGR) and a high Doppler resistance index.
In the media, smooth muscle cells are normally
structured, fusiform, with dens cytoplasm and the nucleus
positioned in the central area. The muscular coat of the
arteries consists of a system of crossing spiraled fibres.
Desmin – positive smooth muscle cells are largely
concetrated on the outer layer of the media. In contrast the
inner media smooth mescle cells are poorly differentiated
with few myofilaments. They can contribute actively to
postpartal closure of the cord arteries [14].
At the umbilical arteries hyaluronic acid was
increased, whereas heparan sulfate and chondroitin 4 and
6 sulfate were reduced in normal umbilical arteries as
compared to normal adult systemic arteries.
The adventitia, which is a heterogeneous layer, is also
predominantly formed by connective tissue with fibrocytes
Clujul Medical 2009 Vol. LXXXII - nr. 3
intercalated with smooth muscle cells, nerves and collagen
fibers. There are not vasa vasorum, or nerves.
Ultrastructural aspects in pregnancy complicated
by severe preeclampsia
In severe preeclampsia, all the layers of the umbilical
arterial wall are affected.
The endothelium undergoes alterations that can
result in the loss of its cells, with serious consequences on
the entire arterial wall. All endothelial cells are columnar,
with reduced cytoplasm and many vacuolizations, and
the nuclei are elongated along the cell axis (Fig. 9). The
number of endothelial cells gradually decreases, both by
the loss of nuclei and the complete detachment of cells and
their fall into the lumen, which results in the presence of
areas without endothelial cells [15,16].
Fig. 9. All endothelial cells are columnar, with reduced cytoplasm
and many vacuolizations, and the nuclei are elongated along the
cell axis.
In parallel to these endothelial alterations, profound
structural disorganization changes occur in the media and
adventitia of the umbilical artery. Smooth muscle cells
undergo shape and structure changes, they are distorted or
segmented. Their cytoplasm is altered, reduced, and nuclei
become pyknotic. Concomitantly with these alterations,
generalized edema occurs, with the formation of large
spaces filled with fluid or vesicular formations containing
material that is probably of lipoprotein nature [17] (Fig 10,
11).
Fig. 10. Interfibrillar spaces are large and contain numerous
vacuolar formations.