Vascular Endothelial Growth Factor Causes Pulmonary Vasodilation through Activation of the Phosphatidylinositol-3-Kinase-Nitric Oxide Pathway in the Late-Gestation Ovine Fetus

Abstract

Vascular endothelial growth factor (VEGF) causes vasodilation in adult models of peripheral vascular disease and myocardial ischemia through the acute release of nitric oxide (NO). However, the hemodynamic effects of VEGF and its effects on NO production have not been studied in the developing lung circulation. We hypothesized that VEGF causes fetal pulmonary vasodilation, and that its actions are mediated through the release of endogenous NO. We performed surgery in 16 fetal lambs (125-135 d gestation; term ϭ 147 d), and placed catheters in the main pulmonary artery, aorta, and left atrium to measure pressures. An ultrasonic flow transducer was placed on the left pulmonary artery (LPA) to measure blood flow, and a catheter was placed in the LPA for local drug infusion. Pulmonary vascular resistance in the left lung was calculated as pulmonary artery pressure minus left atrial pressure divided by LPA flow. Fetal lambs were treated with brief infusions of recombinant human VEGF (dose, 0.5-2.0 g) into the LPA. Recombinant human VEGF infusions acutely increased LPA flow by up to 3-fold (p Ͻ 0.02) and decreased pulmonary vascular resistance by 65% (p Ͻ 0.05) in a dose-related fashion, without affecting aortic pressure or heart rate. To determine the mechanism of VEGF-induced vasodilation, we studied the effects of nitro-Larginine, an NO synthase inhibitor, and LY294002, a phosphatidylinositol-3-kinase inhibitor, on the response to VEGF. We found that pretreatment with either nitro-L-arginine or LY294002 completely inhibited the vasodilator response to recombinant human VEGF (p Ͻ 0.005). These findings suggest that recombinant human VEGF causes fetal pulmonary vasodilation, and that this response is likely mediated by the release of NO through activation of phosphatidylinositol-3-kinase. Abbreviations VEGF, vascular endothelial growth factor NO, nitric oxide NOS, NO synthase MPA, main pulmonary artery Ao, aorta LA, left atrium LPA, left pulmonary artery PVR, pulmonary vascular resistance MPAP, MPA pressure AoP, Ao pressure LAP, LA pressure L-NA, nitro-L-arginine PI-3-K, phosphatidylinositol-3-kinase eNOS, endothelial NOS Qp, pulmonary blood flow BL, baseline HR, heart rate VEGF is a potent endothelial cell mitogen with angiogenic and vascular permeability properties (1-3). VEGF is critical to early vascular development inasmuch as gene ablation of a single allele of VEGF in the mouse prevents normal vascular development and causes early embryonic lethality (4, 5).VEGF signaling not only stimulates vascular growth, but also modulates endothelial cell survival and function (6, 7). In particular, VEGF treatment up-regulates eNOS in endothelial cells in vitro (8) and improves systemic blood flow in vivo (9). Although VEGF is clearly essential for early lung vascular structure and growth, the effects of VEGF on pulmonary vascular tone and reactivity during late fetal life are unclear.Exogenous VEGF administration causes vasodilation in both local and systemic adult vascular beds (10 -12

rhVEGF treatment preserves pulmonary vascular reactivity and structure in an experimental model of pulmonary hypertension in fetal sheep

“…However, significant side effects included systemic hypotension (14,15) and edema at the treatment site (15,32). Animal studies have shown that much lower doses of VEGF are required to improve endothelial cell function and vasodilation and have fewer side effects (11,13,24). Our study utilized these lower doses of VEGF and demonstrated improved endothelium-dependent vasodilation without systemic hypotension or pulmonary edema.…”

“…We have previously shown that VEGF directly stimulates vasodilation in the perinatal pulmonary circulation through stimulation of phosphatidylinositol 3-kinase and subsequent NO release (11). The increase in lung eNOS protein expression after VEGF treatment in lambs with pulmonary hypertension represents improved endothelial function, as also demonstrated by preservation of endothelium-dependent vasodilation and decreased PAP and subsequently decreased pulmonary vascular remodeling.…”

Cardiovascular Effects of Modulators of Soluble Guanylyl Cyclase Activity

“…VEGF apparently plays a major role in the onset of PPHN as it experimentally causes an NO-mediated vasodilation but appears to be suppressed in PPHN [157][158][159]. Just as with other forms of hypertension, NOS uncoupling also seems to be involved [160] although a recent report indicates that uncoupling postnatally creates reactive oxygen species which act as an endothelium-derived hyperpolarizing factor (EDHF) and thus fulfill a regulatory role in the pulmonary circulation of healthy subjects as well [161].…”

Mesenchymal Stem Cells Attenuate Hypoxic Pulmonary Vasoconstriction by a Paracrine Mechanism

“…Tuder et al found that VEGF expression increased in rat lung exposed to hypoxia and may represent a mediator in vessel remodeling in chronic hypoxia [34]. In addition, Grover et al found that VEGF infusion into the pulmonary arteries causes acute vasodilation through the release of NO [22]. Haug et al found that HGF inhibits the release of endothelin-1, thus contributing to vasodilation in coronary arteries [20].…”

“…Hepatocyte growth factor has been shown to directly decrease expression of endothelin, a potent vasoconstrictor [20]. In addition, vascular endothelial growth factor (VEGF) has been shown to cause pulmonary vasodilation [21][22][23]. In chronic hypoxia, neovascularization, angiogenesis, and vessel remodeling can be partly attributed to growth factors [24,25].…”