NITRIC-OXIDE SYNTHASE ACTIVITY IN UMBILICAL AND PLACENTAL VASCULAR TISSUE OF GESTATIONAL DIABETIC PREGNANCIES

Objective: Nitric oxide (NO) synthase activity in the fetal-placental vasculature of gestational diabetic pregnancies was compared to non-di abetic controls. Methods: Placentae were collected from non-diabetic d eliveries (n = 5) and from patients with gestational diabetes (n = 8). Umbilical cord and chorionic plate arteries and veins and stem villou s vessels were quickly dissected out, cleaned of contaminating tissue, snap frozen in liquid nitrogen and stored at -80 degrees C. NO syntha se activity was measured in the homogenate of these vessels by the arg inine to citrulline conversion assay using 5 mu M H-3-L-arginine with 1 mM NADPH, 100 mu M free calcium, 50 units/ml calmodulin, 10 mu M tet rahydrobiopterin and 2 mu M flavin adenine dinucleotide with 45-min in cubation at 27 degrees C. Enzyme activity was expressed as picomoles o f H-3-L-citrulline formed per milligram of protein per minute. Results : No significant differences in NO synthase activity were found betwee n 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 vei n (0.41 +/- 0.15 vs. 0.22 +/- 0.06), respectively (mean +/- SEM). Sign ificantly greater activity was found in stem villous vessels of non-di abetic placentae (5.64 +/- 2.0) compared to those of gestational diabe tic placentae (0.48 +/- 0.19; p < 0.01). Conclusion: The reduced blood flow and increased vascular resistance observed in diabetic pregnanci es may be due to decreased NO synthesis and activity in the stem villo us vessels which are the major determinants of resistance in the fetal -placental vasculature.