Contractile responses of the human umbilical artery from pregnancies complicated by intrauterine growth retardation

Functional and Histological Changes in Umbilical Artery and Myometrium Isolated from IUGR Complicated Pregnancies

Objective: To investigate the relaxation responses mediated by L-type Ca2+ channels and big-conductance Ca2+-activated K+ (BKCa) channels and histological changes in the human umbilical artery (HUA) and myometrium smooth muscle isolated from pregnancies complicated with intrauterine growth restriction (IUGR).Methods: The muscle reactivity and the histology of the smooth muscle of the HUA and myometrium retrieved from 14 women with IUGR and 14 controls were investigated by the isolated tissue bath and immunohistochemical method.Results: In HUA, the maximum relaxation responses and pD2 values of nifedipine and NS11021 (BKCa channel opener) were significantly increased and significant histopathological changes are observed in the IUGR group.Conclusions: The pathogenesis of IUGR might be associated with the impairment in the functional responses of L-type Ca2+ channels and BKCa channels in HUA smooth muscle. The increased staining of myometrium and UC with HIF-1α in IUGR may indicate apoptosis, histological damage, and impaired fetal growth.

Umbilical vein and middle cerebral artery blood flow response to partial occlusion by external compression of the umbilical vein (pressure test)

OBJECTIVES

We studied the responses of flow in the umbilical vein and of the circulation in the proximal segment of the middle cerebral artery (MCA) during partial external compression of the umbilical vein.

METHODS

Partial occlusion of the umbilical vein was achieved by the pressure test, consisting of applying external pressure on the maternal abdominal wall for 1-2 s.

RESULTS

During 60 pressure tests in 45 fetuses with nuchal cords, we observed complete cessation of the umbilical vein flow, while blood flow in the umbilical arteries was preserved, and proximal MCA flow was moderately or markedly decreased. Blood flow in other segments of the MCA was unchanged. This effect, which was more pronounced before the 32nd week of gestation, was also observed in association with spontaneous fetal movements.

CONCLUSION

The pressure test decreases flow in the proximal MCA, and interrupts umbilical vein blood flow. Further analysis of this response suggested the presence of associated vasoconstriction of the proximal MCA.

Computerized microscope morphometry of umbilical vessels from pregnancies with intrauterine growth retardation and abnormal umbilical artery Doppler

Computerized microscope morphometry was used to study cross sections from the vessels of the umbilical cord in placentas of patients with intrauterine growth retardation (IUGR) that displayed either normal or abnormal umbilical arteries (UA) Doppler flow velocity waveforms (FVW). Cords from 63 eutrophic fetuses with normal Doppler (controls), 47 IUGR fetuses with normal Doppler and 32 IUGR fetuses with abnormal Doppler underwent morphometric analysis using a highly optimized microscope environment (HOME) and "CordHOME" software. IUGR with an accompanying normal Doppler versus control showed a reduction of Wharton jelly and both the total and lumen vein areas. IUGR with an accompanying pathological Doppler showed a comparable reduction in wall thickness and areas of every vessel. These findings indicate that the hypoplastic umbilical vessels are associated with an increase in placental vascular resistance that may be the consequence of underdevelopment in response to a chronic reduction in placental blood flow.