Nitric oxide synthase activity in umbilical and placental vascular tissue of gestational diabetic pregnancies

Nitric oxide (NO) synthase activity in the fetal-placental vasculature of gestational diabetic pregnancies was compared to non-diabetic controls.

Placentae were collected from non-diabetic deliveries (n = 5) and from patients with gestational diabetes (n = 8). Umbilical cord and chorionic plate arteries and veins and stem villous vessels were quickly dissected out, cleaned of contaminating tissue, snap frozen in liquid nitrogen and stored at -80 degrees C. NO synthase activity was measured in the homogenate of these vessels by the arginine to citrulline conversion assay using 5 microM 3H-L-arginine with 1 mM NADPH, 100 microM free calcium, 50 units/ml calmodulin, 10 microM tetrahydrobiopterin and 2 microM flavin adenine dinucleotide with 45-min incubation at 27 degrees C. Enzyme activity was expressed as picomoles of 3H-L-citrulline formed per milligram of protein per minute.

No significant differences in NO synthase activity were found between non-diabetic and gestational diabetics for umbilical cord artery (0.58 +/- 0.22 vs. 0.19 +/- 0.06), cord vein (0.39 +/- 0.21 vs. 0.07 +/- 0.03), chorionic plate artery (0.32 +/- 0.14 vs. 0.26 +/- 0.19) or vein (0.41 +/- 0.15 vs. 0.22 +/- 0.06), respectively (mean +/- SEM). Significantly greater activity was found in stem villous vessels of non-diabetic placentae (5.64 +/- 2.0) compared to those of gestational diabetic placentae (0.48 +/- 0.19; p < 0.01).

The reduced blood flow and increased vascular resistance observed in diabetic pregnancies may be due to decreased NO synthesis and activity in the stem villous vessels which are the major determinants of resistance in the fetal-placental vasculature.