Autoradiographic localization of vasoactive intestinal peptide (VIP) binding sites in the human term placenta. Relationship with activation of adenylate cyclase

Placental expression of substance P and vasoactive intestinal peptide: evidence for a local effect on hormone release

The present study evaluated vasoactive intestinal peptide (VIP) and substance P (SP) mRNA expressions and the localization of both peptides in first- and third-trimester human placentas. VIP and SP mRNAs were detected by slot blot analysis in first- and third-trimester placental tissues. By immunohistochemistry both neuropeptides were localized in the trophoblast (syncytium and cytotrophoblastic cells) of the chorionic villi. Because little information is available on the role of VIP and/or SP on the secretion of placental hormones, we investigated the effect of these neuropeptides on human chorionic gonadotropin (hCG) and progesterone release from primary cultured human trophoblastic and JEG-3 cells. The addition of increasing doses of VIP resulted in a dose-dependent stimulation of hCG release from cultured human trophoblast and JEG-3 cells. Increasing doses of VIP also dose-dependently stimulated progesterone secretion from primary cultured trophoblastic cells at all time points evaluated and from JEG-3 cells only after 3 h. SP did not affect hCG and progesterone secretion either in cultured human trophoblast or in JEG-3 cells. In conclusion, the present study demonstrates that VIP and SP are mainly expressed in human trophoblasts, and that VIP modulates the in vitro secretion of hCG and progesterone, suggesting a different role in trophoblastic function of the two peptides.

Vascular effects and cyclic AMP production produced by VIP, PHM, PHV, PACAP-27, PACAP-38, and NPY on rabbit ovarian artery

The relationship between vessel tone and cAMP production induced by vasoactive intestinal polypeptide (VIP), peptide histidine methionine (PHM), peptide histidine valine (PHV), pituitary adenylate cyclase activating polypeptide (PACAP-27 and PACAP-38), and neuropeptide Y (NPY) was investigated in rabbit ovarian arteries in vitro. VIP, PHM, PHV, PACAP-27, and PACAP-38 added in single-dose experiments (10(-9), 10(-8), 10(-7), and 10(-6) M) induced all a significant dose-related relaxation of noradrenaline (NA)-precontracted vessels and displayed similar potencies. VIP, PHM, PHV, PACAP-27, and PACAP-38 all increased cyclic adenosine monophosphate (cAMP) accumulation. The cAMP accumulation induced by PACAP-27 and PACAP-38 was five times higher than the cAMP content induced by the other three peptides. The peptide-induced smooth muscle relaxation did not correlate to the cAMP accumulation. NPY (10(-7) M) markedly reversed the relaxations induced by VIP, PHM, PHV, PACAP-27, and PACAP-38, but did not influence the cAMP production induced by these peptides. In conclusion, the relaxation induced by VIP, PHM, PHV, PACAP-27, and PACAP-38 and the contraction induced by NPY are not solely related to the changes of cAMP contents. These findings indicate that in addition to cAMP, another intracellular signal transduction pathway may be involved in the relaxation and contraction induced by these peptides in rabbit ovarian artery.

Vasoactive intestinal polypeptide and other preprovasoactive intestinal polypeptide-derived peptides in the female and male genital tract: localization, biosynthesis, and functional and clinical significance

Vasoactive intestinal polypeptide, a neuropeptide with wide distribution in the central and peripheral nervous system, has a broad spectrum of biologic actions. The demonstration of vasoactive intestinal polypeptide containing nerve fibers within the female and male genital tract 17 years ago indicated a putative role for this peptide in the local nervous control of reproductive functions. The genes encoding the preprovasoactive intestinal polypeptide precursor molecule and the vasoactive intestinal polypeptide receptor have been identified. The gene expression has been studied by the use of specific antibodies against the functional domains of the vasoactive intestinal polypeptide precursor and the biologic action elucidated by both in vivo and in vitro methods. Evidence has been provided to support vasoactive intestinal polypeptide as a neurotransmitter in several physiologic events in the genital tracts (i.e., blood flow and nonvascular smooth muscle relaxation). In the ovary vasoactive intestinal polypeptide seems to play an important role as regulator and/or modulator of folliculogenesis and steroidogenesis. In the male genital tract vasoactive intestinal polypeptide seems to participate in the control of erection. Vasoactive intestinal polypeptide has been suggested as a causative factor in some diseases of the genital organs (e.g., it may play a pathophysiologic role in male impotence and the peptide is currently used in the treatment of this condition). Vasoactive intestinal polypeptide may be important for control of the low resistance in the fetomaternal vascular bed and is therefore a putative factor involved in the development of preeclampsia. The therapeutic potential of vasoactive intestinal polypeptide and future agonists and antagonists will be revealed by ongoing and forthcoming studies.

The effect of vasoactive intestinal peptide (VIP) on the contractile activity of human uterine smooth muscle

1. In the present study we examined the in vitro effect of vasoactive intestinal peptide (VIP) on spontaneous contractions in both inner and outer layers of non-pregnant human myometrium. A dose-dependent relaxation was observed, but with a marked difference in sensitivity to VIP between the two layers, with an IC50 value of 1 x 10(-8) and 1 x 10(-5) mol L in the outer and inner layers, respectively. 2. We also established that VIP did not directly stimulate the adenylate cyclase activity. The only slight stimulations were observed in non-initial rate conditions. The maximal response of this indirect effect was obtained for VIP concentrations between 1 x 10(-9) and 1 x 10(-8) mol/L and this occurred to the same extent (an approximately 1.4-fold increase) in both layers. However this response is specific, since structurally related peptides such as glucagon, gastric inhibitory polypeptide (GIP), secretin, or human growth hormone-releasing factor (hGRF) had no effect in our preparations. 3. Autoradiographic studies revealed that specific VIP binding sites were located on the vascularization of the intermediate vascular layer and on arterioles and venules distributed in the inner and outer myometrial layers. They were also present in the endometrium, but not on smooth muscle cells of either layer. 4. Such observations could provide evidence for another signal transduction pathway to mediate the biological effect of VIP. An additional intermediate step on the vascularization distributed in all of the muscle cannot be excluded.

Regional distribution and pharmacological characterization of [125I]endothelin-1 binding sites in human fetal placental vessels

High-affinity binding sites for [125I]endothelin(ET)-1 have been detected in purified membrane preparations of the fetal arteries and veins of the chorionic plate and the stem villi vessels of the human term placenta. Regardless of the vessel type, the apparent dissociation constant was found to be in the picomolar range (26----45 pM), and the Bmax value close to 600 fmol/mg protein. In stem villi vessels, ET-1, ET-2, sarafotoxin S6b and vasocontractor intestinal peptide (VIC) were approximately equipotent in their competitive displacement of [125I]ET-1 binding. The endothelin precursors, human and porcine big-endothelin, recognized ET-1 sites with low affinity (nM range), a finding which reflects their low potency as recognized vasocontractant agents. Interestingly, [125I]ET-1 binding parameters and pharmacological profiles were identical in fetal veins and arteries of the chorionic plate. Similarly, a study carried out in rat aortic membranes, revealed the presence of high affinity [125I]ET-1 binding sites with pharmacological characteristics close to those of the human stem villi vessels. In all vessels investigated, the binding pattern of ET-3 against [125I]ET-1 was of a non-competitive nature. Thus, these results demonstrate the presence of specific [125I]ET-1 binding sites along the vascular tree of the fetal side of the placenta and would support evidence currently available, favouring the existence of distinct ET-1 and ET-3 receptors. Finally, ET-1 in the human placenta may play an important physiological role as regulator of vascular resistance and/or be implicated as a pathological factor in certain pregnancy-related diseases.

Regulatory peptides in the mammalian urogenital system

By immunocytochemistry a number of the gut/brain peptides have been demonstrated in nerve fibers of the mammalian urogenital tract. These peptides are localized to large vesicles in nerve terminals of afferent fibers or efferent nerves innervating blood vessels, non-vascular smooth muscle, lining epithelium and glands. There is evidence that some neuropeptides (VIP, NPY) participate in the local non-cholinergic, non-adrenergic nervous control of smooth muscle activity and blood flow, while other peptides (substance P, CGRP) seem to be sensory transmitters. It is likely that impaired function of the peptidergic nerves is involved in sexual dysfunction such as male impotence.