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

Both the Suprachiasmatic Nucleus and the Superior Ovarian Nerve Contribute to the Processes of Ovulation and Steroid Hormone Secretion on Proestrus

The aims of the present study were to analyze if the superior ovarian nerve (SON) plays a role in the neural signals from suprachiasmatic nucleus (SCN) that lead to ovulation and ovarian steroids secretion on proestrus day. Rats on proestrus day were treated at 11.00 to 11.30 or 17.00 to 17.30 hours with 1 of the 3 experimental procedures (1) unilateral or bilateral SON sectioning, (2) unilateral or bilateral injury to the SCN, or (3) unilateral injury to the SCN followed by unilateral sectioning of the SON ipsilateral to the treated SCN. Treatments were evaluated 24 hours after surgical procedures. Compared to laparotomized animals, right or bilateral SON sectioning treatment at 17.00 hours resulted in lower ovulation rates and number of ova shed by the right ovary. The ovaries of nonovulating animals showed early follicular luteinization signs and trapped ova. Bilateral SCN injury treatment at 11.00 hours resulted in anovulation; whereas right SCN injury treatment, with or without right SON sectioning, resulted in a lower number of ova shed. Injecting luteinizing hormone-releasing hormone to animals with bilateral SCN injury restored ovulation. In rats with unilateral or bilateral SON sectioning, or with injury to the SCN with or without unilateral sectioning of the SON, the effects on hormone levels depended of the hormone studied and the time of day treatment was performed. The present results suggest that on proestrus day, the role of the right or both SON in ovulation and steroid hormone secretion regulation takes place through different neuroendocrine mechanisms from SCN.

Vasoactive Intestinal Polypeptide Evokes Only a Minimal Headache in Healthy Volunteers

The role of the parasympathetic nervous system in the pathogenesis of migraine is disputed. The headache-eliciting effect of the parasympathetic neurotransmitter, vasoactive intestinal polypeptide (VIP), and its effect on cerebral arteries and brain haemodynamics has not been systematically studied in man. We hypothesized that infusion of VIP might induce headache in healthy subjects and cause changes in cerebral haemodynamics. VIP (8 pmol/kg per min) or placebo (0.9± saline) was infused for 25 min into 12 healthy young volunteers in a crossover, double-blind design. Headache was scored on a verbal rating scale from 0 to 10, regional cerebral blood flow (rCBF) was measured with single-photon emission computed tomography and 133Xe inhalation and mean flow velocity in the middle cerebral artery (VmeanMCA) was measured with transcranial Doppler ultrasonography. The headache was very mild with a maximum score of 2 and described as a pressing or throbbing sensation. Five participants developed headache during VIP and one during placebo. During the infusion, a significant drop in VmeanMCA was seen for VIP compared with placebo ( P < 0.001), but the effect quickly waned and no difference was found when comparing the time between 30 and 120 min. In addition, no significant difference in the diameter of the MCA could be found during the infusion. No significant differences in rCBF ( P = 0.10) were found between VIP and placebo. A marked dilation of the superficial temporal artery was seen ( P = 0.04) after VIP in the first 30 min but no difference was found when comparing the time between 30 and 120 min. We found no difference in mean arterial blood pressure between VIP and placebo days but the heart rate increased significantly on a VIP day compared with a placebo day (AUC0–30min, P < 0.001). Plasma VIP was significantly higher on a VIP day compared with placebo (AUC0–80min, P < 0.001). These results show that VIP causes a decrease in VmeanMCA without affecting rCBF. In spite of a marked vasodilator effect in the extracranial vessels and increased plasma VIP, healthy subjects developed only a very mild headache.

Effect of hyperoxic and hyperbaric conditions on the adenosinergic pathway and CD26 expression in rat

The nucleoside adenosine acts on the nervous and cardiovascular systems via the A2A receptor (A2AR). In response to oxygen level in tissues, adenosine plasma concentration is regulated in particular via its synthesis by CD73 and via its degradation by adenosine deaminase (ADA). The cell-surface endopeptidase CD26 controls the concentration of vasoactive and antioxidant peptides and hence regulates the oxygen supply to tissues and oxidative stress response. Although overexpression of adenosine, CD73, ADA, A2AR, and CD26 in response to hypoxia is well documented, the effects of hyperoxic and hyperbaric conditions on these elements deserve further consideration. Rats and a murine Chem-3 cell line that expresses A2AR were exposed to 0.21 bar O2, 0.79 bar N2 (terrestrial conditions; normoxia); 1 bar O2 (hyperoxia); 2 bar O2 (hyperbaric hyperoxia); 0.21 bar O2, 1.79 bar N2 (hyperbaria). Adenosine plasma concentration, CD73, ADA, A2AR expression, and CD26 activity were addressed in vivo, and cAMP production was addressed in cellulo. For in vivo conditions, 1) hyperoxia decreased adenosine plasma level and T cell surface CD26 activity, whereas it increased CD73 expression and ADA level; 2) hyperbaric hyperoxia tended to amplify the trend; and 3) hyperbaria alone lacked significant influence on these parameters. In the brain and in cellulo, 1) hyperoxia decreased A2AR expression; 2) hyperbaric hyperoxia amplified the trend; and 3) hyperbaria alone exhibited the strongest effect. We found a similar pattern regarding both A2AR mRNA synthesis in the brain and cAMP production in Chem-3 cells. Thus a high oxygen level tended to downregulate the adenosinergic pathway and CD26 activity. Hyperbaria alone affected only A2AR expression and cAMP production. We discuss how such mechanisms triggered by hyperoxygenation can limit, through vasoconstriction, the oxygen supply to tissues and the production of reactive oxygen species.

Pituitary adenylate cyclase activating polypeptide: an important vascular regulator in human skin in vivo

Pituitary adenylate cyclase-activating peptide (PACAP) is an important neuropeptide and immunomodulator in various tissues. Although this peptide and its receptors (ie, VPAC1R, VPAC2R, and PAC1R) are expressed in human skin, their biological roles are unknown. Therefore, we tested whether PACAP regulates vascular responses in human skin in vivo. When injected intravenously, PACAP induced a significant, concentration-dependent vascular response (ie, flush, erythema, edema) and mediated a significant and concentration-dependent increase in intrarectal body temperature that peaked at 2.7°C. Topical application of PACAP induced marked concentration-dependent edema. Immunohistochemistry revealed a close association of PACAP-immunoreactive nerve fibers with mast cells and dermal blood vessels. VPAC1R was expressed by dermal endothelial cells, CD4+ and CD8+ T cells, mast cells, and keratinocytes, whereas VPAC2R was expressed only in keratinocytes. VPAC1R protein and mRNA were also detected in human dermal microvascular endothelial cells. The PACAP-induced change in cAMP production in these cells demonstrated VPAC1R to be functional. PACAP treatment of organ-cultured human skin strongly increased the number of CD31+ vessel cross-sections. Taken together, these results suggest that PACAP directly induces vascular responses that may be associated with neurogenic inflammation, indicating for the first time that PACAP may be a crucial vascular regulator in human skin in vivo. Antagonists to PACAP function may be beneficial for the treatment of inflammatory skin diseases with a neurogenic component.

Involvement of endothelial NO in the dilator effect of VIP on rat isolated pulmonary artery

The endothelium and its interaction with smooth muscle play a central role in the local control of the pulmonary vasculature, and endothelial dysfunction is thought to contribute to pulmonary hypertension and chronic obstructive pulmonary disease. Vasoactive intestinal peptide (VIP), a 28-amino acid neuropeptide, relaxes the rat pulmonary artery, but there is controversy as to whether or not this action of VIP depends on the endothelium. The aim of this study, therefore, was to investigate the role of the endothelium and nitric oxide (NO), the major endothelium-derived relaxing factor, in the dilator action of VIP on the rat isolated pulmonary artery. Pulmonary artery preparations pre-contracted by the alpha(1)-adrenoceptor agonist L-phenylephrine were relaxed by VIP (0.003-1 microM) and acetylcholine (0.003-10 microM) in a concentration-dependent manner. Mechanical removal of the endothelium reduced the maximal response to VIP by about 50% and practically abolished the response to acetylcholine. Inhibition of NO synthesis by N(omega)-nitro-L-arginine methyl ester (0.5 mM) had a similar effect, abolishing the vasorelaxation caused by acetylcholine and attenuating the vasorelaxation caused by VIP by about 50%. From these data it is concluded that the relaxant action of VIP on the rat isolated pulmonary artery depends in part on the presence of the endothelium and that this part is mediated by endothelial NO.

Coronary vascular effects of vasoactive intestinal peptide in the isolated perfused rat heart

The potency and mechanism of action of vasoactive intestinal peptide (VIP) for producing coronary vasodilation was investigated in the isolated perfused heart of the rat. VIP reduced coronary vascular resistance in a dose-dependent manner, starting at 1 x 10(-10) M, and maximally reduced coronary vascular resistance by 49% at 1 x 10(-8) M. The potency of VIP for reducing coronary vascular resistance (EC50=3.02 x 10(-10) M) was considerably greater than that of adenosine (EC50=6.17 x 10(-8) M) and sodium nitroprusside (EC50=2.45 x 10(-6) M). The vasodilatory action of VIP was more easily observed after increasing vascular tone by perfusion of the hearts with a modified physiological solution containing reduced concentrations of potassium (3.2 mM) and calcium (1.2 mM). Under these conditions, VIP maximally reduced coronary resistance by 54% at 7 x 10(-9) M. The potency of VIP for reducing coronary resistance in these hearts, however, decreased 16-fold (EC50=4.90 x 10(-9) M) while that of SNP remained unaltered (EC50=3.39 x 10(-6) M), compared with hearts perfused with higher levels of potassium (5.9 mM) and calcium (2.5 mM). The vasodilatory effect of VIP occurred without a significant change in heart rate, myocardial contractility or oxygen consumption. In additional studies, the dose-dependent effect of VIP on cyclic nucleotide release from the heart was determined by infusing VIP into the coronary circulation in a cumulative fashion to produce final concentrations between 1 x 10(-11) and 1 x 10(-9) M. VIP increased cyclic AMP at 1 x 10(-9) M but did not increase cyclic GMP. Studies using RT-PCR and immunohistochemistry clearly demonstrated the presence of two VIP receptor subtypes, VPAC1 and VPAC2, in the arteries and arterioles of the heart. In conclusion, VIP is a potent vasodilator in the coronary circulation of the rat and the role of VIP in the control of coronary vascular resistance depends on the circulating levels of potassium and calcium. This vasodilatory effect involves binding to specific coronary cell surface receptors, VPAC1 and/or VPAC2, and is dependent on cyclic AMP only during maximal vasodilation.

Neuritogenesis induced by vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, and peptide histidine methionine in SH-SY5y cells is associated with regulated expression of cytoskeleton mRNAs and proteins

Vasoactive intestinal peptide (VIP) and the related peptides pituitary adenylate cyclase-activating polypeptide (PACAP) and peptide histidine methionine (PHM) are known to regulate proliferation and/or differentiation in normal and tumoral cells. In this study, neuritogenesis in human neuroblastoma SH-SY5Y cells cultured in serum-free medium was induced by VIP, PACAP, and PHM. The establishment of this process was followed by the quantification of neurite length and branching and the expression of neurofilament mRNAs, neurofilament proteins, and other cytoskeletal protein markers of neuronal differentiation: neuron-specific MAPs and beta-tubulin III. Neurite length and branching and the expression of most markers tested were increased by VIP and PACAP in a similar, although slightly different, fashion. In contrast, neuritic elongation induced by PHM was correlated with neither an increase in branching or neurofilament mRNAs nor a clear change in the expression of cytoskeleton proteins, with the exception of the stimulation by PHM of doublecortin, a microtubule-associated marker of migrating neuroblasts. These findings are the first evidence from a human neuron-like cell line for 1) a direct regulation of the metabolism of neurofilaments by VIP and PACAP and 2) the induction by PHM of neuritic processes of an apparent immature character.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Vasoactive intestinal polypeptide stimulates the proliferation of HaCaT cell via TGF-alpha

It is well known that psoriasis, an immunogenetic cutaneous disorder whose major pathogenic findings are epidermal hyperplasia and T-cell infiltration, is aggravated by psychological stresses. Although the exact mechanism is not yet clarified, antidromic secretion of neuropeptides by cutaneous nerve fibers is thought to be involved. In this study, we examined the effect and mechanism of vasoactive intestinal polypeptide (VIP), one of the major neuropeptides, on the proliferation of HaCaT cell which is a spontaneous, immortalized, human keratinocyte cell line. Twenty-four and 48 h after its addition, 1 pM to 100 nM of VIP increased the number of cells cultured with/without serum. We indirectly verified VIP(1)R on the surface of HaCaT cell based on the proliferative ability of various VIP families such as VIP, PACAP and secretin, and increased PKA level 30 min after stimulation. However, because H-89, a PKA inhibitor, did not inhibit the proliferative potential of VIP, its mitogenicity is not medicated through VIP(1)R. One nM VIP produced the TGF-alpha protein which is a strong mitogen of keratinocytes and increased in the psoriatic lesion 2.25 times more compared with the control. Genistein, a tyrosine kinase inhibitor, abrogated the mitogenic activity of VIP. Like VIP, VIP fragments, VIP(1-12) and VIP(10-28) also acted as a mitogen for HaCaT cells through the same mechanism. Collectively, our studies clearly show that VIP and its fragments stimulate keratinocyte growth, not through increased cAMP level, but through increased TGF-alpha protein production.

The effect of neuropeptides on vessel tone and cAMP production

The effect of VIP, PHM, PHV, PACAP-27, and PACAP-38 on vessel tone and cAMP production was investigated in rabbit ovarian arteries in vitro. The peptides (10(-7)M) induced a significant relaxation on NA-precontracted vessels and displayed similar potencies. The cAMP accumulation induced by PACAP-27 and PACAP-38 was five times higher than the cAMP content induced by VIP, PHM, and PHV. NPY (10(-7)M) markedly reversed the relaxations induced by VIP, PHM, PHV, PACAP-27, and PACAP-38 but did not at all affect the cAMP production induced by these peptides. We conclude that the relaxation induced by VIP, PHM, PHV, PACAP-27, and PACAP-38 and the contraction evoked by NPY are not solely related to the changes of cAMP contents, and that in addition to cAMP, another intracellular signal transduction pathway may be involved.