ELECTRON-MICROSCOPIC IMMUNOLABELING OF VASOACTIVE SUBSTANCES IN HUMANUMBILICAL ENDOTHELIAL-CELLS AND THEIR ACTIONS IN EARLY AND LATE PREGNANCY

Human umbilical vessels are devoid of nerves and therefore endothelial cells may play an important role in the control of fete-placental blo od flow. The pharmacological effects of 5-hydroxytryptamine, histamine and endothelin were examined in umbilical arteries and veins from leg al terminations (gestational age 8-17 weeks, n=12) and normal term vag inal deliveries (gestational age 38-41, n=12). Immunocytochemistry of human unbilical vessels indicated that 5-hydroxytryptamine, histamine and endothelin were localised in subpopulations of endothelial cells o f both artery and vein in late, but not early, pregnancy. 5-Hydroxytry ptamine (10 nM-30 mu M) caused sustained concentration-dependent contr actions in all vessels from early and late pregnancy. Histamine (0.1 m u M-30 mM) also caused sustained contractions in all vessels from late pregnancy but only 27% of arteries and 41% of veins from early pregna ncy responded. Endothelin (10 pM-30 nM) caused slow long-lasting contr actions in all vessels from early and late pregnancy. Atrial natriuret ic peptide and neuropeptide Y did not alter vascular tone. The endothe lium may thus play an autocrine/paracrine role, by synthesizing and re leasing the above reactive substances in late pregnancy to influence f ete-placental blood flow.