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 4-6 weeks until delivery, 29 of them were additionally investigated postpartum. Paralleling each Doppler sonographic 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 re-increase 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.