Decreasing resistance in the maternal uterine and peripheral arterial system is apparently unrelated to plasma and urinary levels of nitrite/nitrate and cyclic-guanosinmonophosohate during the course of normal pregnancies

Aims: The aim of the presented study was to clarify the
relationship between the pulsatility index of the uterine arteries
and the maternal cubital artery and peripheral concentrations of
the metabolites of nitric oxide (NO) and its second messenger
cyclic guanosinmonophophate (cGMP) during the normal course of
pregnancy and postpartum. Methods: 49 uncomplicated pregnancies
were investigated every 46 weeks until delivery, 29 of them were
additionally investigated postpartum. Paralleling each Doppler
sonografic investigation maternal blood and urine samples were
taken. The measurements of nitrite/ nitrate and cGMP were performed
with a colorimetric and radio immuno assay. We demonstrate a
significant decrease of the PI of the uterine arteries and of the
cubital artery with inverse correlation to advancing gestational
age. Results: The concentrations of nitrite/nitrate and cGMP remain
stable during gestation and do not correlate to the PI of the
uterine and cubital artery. Postpartum a reincrease in the uterine
and peripheral resistance can be shown. The concentrations of
urinary cGMP and nitrite/ nitrate as well as plasma cGMP remain
unchanged, whereas plasma nitrite/nitrate decreases postpartum.
Conclusions: The status of NO biosyntheses in normal pregnancy
remains controversial. We hypothesize further systemically acting
mediators which contribute to the decreasing vascular resistance.