Localization of neuropeptide Y and atrial natriuretic peptide in the endothelial cells of human umbilical blood vessels

NPY in rat retina is present in neurons, in endothelial cells and also in microglial and Müller cells

NPY is present in the retina of different species but its role is not elucidated yet. In this work, using different rat retina in vitro models (whole retina, retinal cells in culture, microglial cell cultures, rat Müller cell line and retina endothelial cell line), we demonstrated that NPY staining is present in the retina in different cell types: neurons, macroglial, microglial and endothelial cells. Retinal cells in culture express NPY Y(1), Y(2), Y(4) and Y(5) receptors. Retina endothelial cells express all NPY receptors except NPY Y(5) receptor. Moreover, NPY is released from retinal cells in culture upon depolarization. In this study we showed for the first time that NPY is present in rat retina microglial cells and also in rat Müller cells. These in vitro models may open new perspectives to study the physiology and the potential pathophysiological role of NPY in the retina.

Umbilical vein constriction at the umbilical ring: a longitudinal study

OBJECTIVE

It has been suggested that constriction of the umbilical vein (UV) at the umbilical ring has hemodynamic effects. We aimed to determine the occurrence and extent of such constriction in serial observations.

METHODS

This was a prospective longitudinal study of UV velocities at the umbilicus measured at approximately 4-week intervals between 19 and 42 weeks' gestation in 129 low-risk singleton pregnancies. Each participant was examined three to five times. Multilevel modeling was used to construct the reference ranges and to test associations between variables.

RESULTS

Gestational age-specific reference percentiles of UV velocities at the umbilicus were established based on 469 observations. Fetuses were able to alter the UV velocities considerably during the second half of pregnancy, signifying a varying degree of UV constriction. Of a total of 129 fetuses, 56 (43.4%) never had high UV blood velocity (i.e. > 46 cm/s, the highest quartile), 42 (32.6%) fetuses had high UV blood velocity on one occasion and 31 (24.0%) fetuses on two or more occasions. In 36 (27.9%) fetuses the UV velocity at the umbilical ring was > 300% of the mean gestational age-specific reference value at the intra-abdominal section on at least one occasion. Constriction of the UV at the umbilical ring did not affect the pulsatility of the umbilical artery, and was not associated with adverse perinatal outcome in this study.

CONCLUSIONS

Low-risk fetuses may well constrict the UV at the abdominal wall with velocities extending over wide ranges on one or more occasions during the second half of pregnancy. Rather than being a risk for complications, the constriction seems to be part of physiological development and possibly a regulatory mechanism.

Neuropeptide Y expression, localization and cellular transducing effects in HUVEC

BACKGROUND INFORMATION

NPY (neuropeptide Y) may have an effect on the properties of vascular endothelial cells such as pro-angiogenic effects and potentiation of noradrenaline-induced vasoconstriction. In HUVEC (human umbilical-vein endothelial cells), immunoreactive neuropeptide Y has been detected, but NPY synthesis, storage and secretion have not been studied. The aim of the present study was to establish NPY expression, storage and cellular transducing effects in HUVEC.

RESULTS

HUVEC contain 0.19 fmol of NPY/microg of protein and 0.46 fmol of pro-NPY/microg of protein, as measured by ELISA. RT (reverse transcriptase)-PCR confirmed the expression of NPY in HUVEC. Immunofluorescence revealed the presence of NPY in small punctate structures, with a fluorescence pattern different from that observed for von Willebrand factor, indicating distinct storage compartments. Double labelling for NPY and Rab3A demonstrated similar granular patterns, with at least partial co-localization. Electron microscopy showed NPY immunoreactivity in vesicle-like cytoplasmic structures, of a fine fibrillar texture, as well as in mitochondria and in the nucleus. A similar general distribution pattern was also obtained for Rab3A. Y1 and Y2 receptors were expressed in HUVEC as assessed by RT-PCR, and they were functional since NPY induced a 42 nM intracellular calcium increase within 100 s, representing 22% of the histamine-induced response. In contrast with histamine, NPY did not induce acute von Willebrand factor secretion.

CONCLUSIONS

HUVEC produce, store and respond to NPY, suggesting an autocrine regulatory role for NPY in the endothelium.

Pituitary adenylate cyclase activating polypeptide (PACAP): occurrence and vasodilatory effect in the human uteroplacental unit

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide which was originally isolated from ovine hypothalamus. PACAP exists in at least two biologically active forms, PACAP-38 and PACAP-27. The aim of this study was to establish the distribution, localization and smooth muscle effects of PACAP-38 and PACAP-27 in the human uteroplacental unit. For this purpose we used radioimmunoassay, immunocytochemistry and in vitro studies of the effect of the peptides on smooth muscle activity.

RESULTS

By radioimmunoassay both peptides were detected throughout the uteroplacental unit. The concentrations of PACAP-27 were in general low, ranging from 1/6-1/25 of the corresponding PACAP-38 concentrations. PACAP-immunoreactivity was localized in nerve fibres of the lower segment of the pregnant uterus, but the number of PACAP-immunoreactive nerves was very clearly reduced compared to the corresponding isthmic region of non-pregnant myometrial tissue. PACAP-immunoreactive fibres were not observed in placenta or in the umbilical cord. Both PACAP-38 and PACAP-27 caused a concentration-dependent relaxation on stem villous arteries and on the intramyometrial arteries. Neither of the peptides displayed any effect on non-vascular smooth muscle specimens from the term pregnant myometrium. In conclusion the findings suggest a vasoregulator role of PACAP in the human uteroplacental unit.

Nitric oxide and human umbilical vessels: pharmacological and immunohistochemical studies

Human umbilical vessels are devoid of nerves and therefore endothelial cells may play an important role in the control of fetoplacental blood flow. In this study we examined the pharmacological effects of various substances, known to produce endothelial-mediated vasodilation in many blood vessels, on the human umbilical artery and vein from legal terminations [mean gestational age, 15 (8-17) weeks; n = 12] and normal term vaginal deliveries [mean gestational age, 39 (38-41) weeks; n = 12]. Acetylcholine, adenosine 5'-triphosphate, the calcium ionophore A23187 and substance P had no effect on raised vascular tone, whereas sodium nitroprusside relaxed 5-hydroxytryptamine (5-HT) preconstricted, umbilical artery and vein from both early and late pregnancy. L-NG-Nitroarginine methyl ester (L-NAME) had no effect on basal tone or on high tone, after it was raised by 5-HT. Localization of nitric oxide synthase [NOS, type I (neuronal)] was examined in the same umbilical vessels using electron immunocytochemistry. No NOS-immunoreactive endothelial cells were observed in the umbilical vessels taken during early pregnancy. However, the percentage of NOS-immunoreactive endothelial cells in umbilical artery and vein from late pregnancy was 3 and 10 per cent, respectively. These results suggest that nitric oxide contributes little, if any, to the local control of umbilical blood flow throughout pregnancy, despite the presence of NOS-immunoreactivity in a subpopulation of endothelial cells in late pregnancy.

New insights into the local regulation of blood flow by perivascular nerves and endothelium

Blood flow, particularly in the skin, is essential for the success of plastic surgical operations. This review describes recent studies of the perivascular nerves and vascular endothelial cells which regulate blood flow. Perivascular nerves, once considered simply adrenergic or cholinergic, release many types of neurotransmitters, including peptides, purines and nitric oxide. Cotransmission (synthesis, storage and release of more than one transmitter by a single nerve) commonly takes place. Some afferent nerves have an efferent (motor) function and axon reflex control of vascular tone by these "sensory-motor" nerves is more widespread than once thought. Endothelial cells mediate both vasodilatation and vasoconstriction. The endothelial cells can store and release vasoactive substances such as acetylcholine (vasodilator) and endothelin (vasoconstrictor). The origins and functions of such vasoactive substances are discussed. Endothelial vasoactive substances may be of greater significance in the response of blood vessels to local changes while perivascular nerves may be concerned with integration of blood flow in the whole organism. The dual regulation of vascular tone by perivascular nerves and endothelial cells is altered by aging and conditions such as hypertension, as well as by trauma and surgery. Studies of vascular tone in disease and after denervation or mechanical injury suggest possible trophic interactions between perivascular nerves and endothelial cells. Such trophic interactions may be important for growth and development of the two control systems, particularly in the microvasculature where neural-endothelial separation is small.

Colocalization of vasoactive substances in the endothelial cells of human umbilical vessels

Human umbilical vessels are unique in lacking any innervation; thus endothelial cells may play the major role in local control and regulation of the blood flow. In the present study, we examined ultrathin sections of cultured human umbilical vein endothelial cells and tissue preparations of umbilical vein and artery, immunostained by the post-embedding colloidal gold double-labelling technique. We observed colocalization of atrial natriuretic peptide and neuropeptide Y, as well as colocalization of atrial natriuretic peptide and neuropeptide Y with other vasoactive substances, namely, vasoactive intestinal peptide, substance P, calcitonin gene-related peptide and arginine vasopressin. The functional significance of the colocalization of these vasoactive substances in the human umbilical vessel endothelial cells is discussed.