Fetal and maternal plasma levels of immunoreactive somatostatin at delivery: evidence for its increase in the umbilical artery and its arterio-venous gradient in the feto-placental circulation.

The concentrations of immunoreactive somatostatin (IR-SRIF) in plasma samples taken from the umbilical artery (UA), umbilical vein (UV), and maternal antecubital vein (MV) were measured in 23 cases of normal delivery at term. High concentrations of IR-SRIF were detected in the plasma from the UA (mean +/- SD, 73.2 +/- 40.6 pg/ml), the value being about 2.5 times that in the UV (29.5 +/- 17.5 pg/ml; P less than 0.001). An arterio-venous gradient was observed in all 23 subjects. The plasma level of IR-SRIF in the MV (10.9 +/- 4.6 pg/ml) was significantly lower than those in the UA (P less than 0.001) and UV (P less than 0.001) and was almost the same as that in nonpregnant women (12.7 +/- 5.4 pg/ml). Chromatographic analysis of an extract of plasma from the UA gave only one peak of immunoreactive material, which was eluted in the same position as synthetic SRIF-14. A similar result was obtained in nonpregnant women. No correlation was found between the plasma level of IR-SRIF and that of GH, insulin, glucagon, or gastrin in the UA. The present findings suggest that the high concentration of IR-SRIF in the feto-placental circulation originates from the fetus and reflects a particular role of this peptide in the process of functional maturation of the neuroendocrine system in early human life.