Nitric oxide synthase in human placenta and umbilical cord from normal, intrauterine growth-retarded and pre-eclamptic pregnancies

1 It has been suggested that a deficiency of nitric oxide (NO) may explain many of the pathophysiological features of pre-eclampsia (PE) and intra-uterine (foetal) growth retardation (IUGR). To elucidate further the role of NO in the pathophysiology of pregnancy we have determined the relative amount and activity of NO synthase (NOS) in first trimester and normal-term placental tissues, as well as in the placenta and umbilical cord in pregnancies complicated by PE and IUGR, using N-G-nitro-L-[2,3,4,5-H-3]-arginine ([H-3]-L-NOARG) binding, quantitative in vitro autoradiography, [H-3]-arginine to [H-3]-citrulline conversion and Western blotting. 2 Specific, high affinity (K-D=38 nM) [H-3]-L-NOARG binding was demonstrated in the villous trophoblast of normal-term placentae. Binding was calcium-independent, stereoselective and exhibited a rank order of inhibition by NOS inhibitors and substrate (L-NOARG greater than or equal to L-NMMA greater than or equal to 7-NI>L-NAME>L-Arg greater than or equal to L-NIO>ADMA). 3 [H-3]-L-NOARG binding density and NOS activity were both significantly greater in placental tissues from first trimester and PE or IUGR complicated pregnancies compared to normal-term placentae. 4 Western blotting, using an endothelial NOS peptide antiserum, demonstrated a similar to 140 KDa protein band in placental extracts and indicated that the amount of immunoreactive material was significantly greater in first trimester compared to normal-term placentae. 5 Specific [H-3]-L-NOARG binding was also localized to the endothelial lining of umbilical arteries and veins, binding density being greater in the artery than the vein. [H-3]-L-NOARG binding to the umbilical artery endothelium was significantly lower in PE and IUGR complicated pregnancies compared to normal-term controls. 6 The role of trophoblast-derived NO in human placental pathophysiology remains to be established, but differences in the amount of placental [H-3]-L-NOARG binding, NOS activity and immunoreactive material indicate that expression of NOS in the villous trophoblast falls during pregnancy. Conversely, the apparent reduction in NOS in the umbilical artery endothelium in PE and IUGR complicated pregnancies may be indicative of endothelial dysfunction.