Emily Wilson

Adaptation of mesenteric lymphatic vessels to prolonged changes in transmural pressure

In vitro studies have revealed that acute increases in transmural pressure increase lymphatic vessel contractile function. However, adaptive responses to prolonged changes in transmural pressure in vivo have not been reported. Therefore, we developed a novel bovine mesenteric lymphatic partial constriction model to test the hypothesis that lymphatic vessels exposed to higher transmural pressures adapt functionally to become stronger pumps than vessels exposed to lower transmural pressures. Postnodal mesenteric lymphatic vessels were partially constricted for 3 days. On postoperative day 3, constricted vessels were isolated, and divided into upstream (UP) and downstream (DN) segment groups, and instrumented in an isolated bath. Although there were no differences between the passive diameters of the two groups, both diastolic diameter and systolic diameter were significantly larger in the UP group than in the DN group. The pump index of the UP group was also higher than that in the DN group. In conclusion, this is the first work to report how lymphatic vessels adapt to prolonged changes in transmural pressure in vivo. Our results suggest that vessel segments upstream of the constriction adapt to become both better fluid conduits and lymphatic pumps than downstream segments.

NF-κB and matrix-dependent regulation of osteopontin promoter activity in allylamine-activated vascular smooth muscle cells.

Repeated cycles of oxidative injury by allylamine in vivo induce a proliferative rat vascular (aortic) smooth muscle cell (vSMC) phenotype characterized by matrix-dependent enhancement of mitogenic sensitivity, changes in cell surface integrin expression, and osteopontin (opn) overexpression. Here, we show that constitutive and mitogen-stimulated NF-κB DNA binding activity is enhanced in allylamine vSMCs. Matrix-specific changes in cellular Rel protein expression were observed in allylamine vSMCs. The NF-κB DNA binding element located at −1943 in the 5′-UTR strongly inhibited opn promoter activity in allylamine vSMCs, and this response was regulated by the extracellular matrix. Constitutive increases in opn promoter activity were only seen when allylamine cells were seeded on a fibronectin substrate, and this response was independent of the NF-κB DNA binding sequence within the regulatory region. Thus, NF-κB functions as a critical regulator of the allylamine-induced proliferative phenotype in vSMCs.

Modulation of cyclin dependent kinase inhibitor proteins and ERK1/2 activity in allylamine-injured vascular smooth muscle cells

Chronic oxidative injury by allylamine (AAM) induces proliferative vascular smooth muscle cell (vSMC) phenotypes in the rat aorta similar to those seen in rodent and human atherosclerotic lesions. The proliferative advantage of AAM vSMC compared to control cells is maintained with serial passage of the cells and the advantage is nullified when AAM cells are seeded on a collagen substrate. In this study, we evaluate the potential role of cyclin dependent kinase inhibitors, p27 and p21, and mitogen activated protein (MAP) kinases, ERK1/2, in mediating the proliferative advantage of AAM stressed vSMC over control cells on plastic or collagen substrates. p27 levels in randomly cycling cells were comparable in both cell types irrespective of the substrate. In contrast, basal levels of p21 were 1.9u2009±u20090.3 (Pu2009<u20090.05)‐fold higher in randomly cycling AAM cells seeded on plastic compared to controls, a difference that was lost on a collagen substrate. Following G0 synchronization, basal levels of both p27 and p21 were higher in AAM cells seeded on plastic compared to controls (1.7u2009±u20090.2 and 2.0u2009±u20090.3‐fold, respectively, Pu2009<u20090.05), but these differences were lost upon mitogenic stimulation. Pyrrolidine dithiocarbamate (PDTC) decreased p27 and p21 levels in cycling AAM cells relative to controls in a substrate‐dependent manner. AAM cells seeded on plastic exhibited enhanced ERK1/2 activation upon mitogenic stimulation; seeding on collagen nullified this advantage. The duration of ERK1/2 activation was prolonged in AAM cells independently of the seeding substrate. We conclude that substrate‐dependent acquisition of proliferative phenotypes following repeated cycles of AAM injury correlates with modulation of the cyclin dependent kinase inhibitors, p27 and p21.

Short-duration increases in intraluminal pressure improve vasoconstrictor responses in aged skeletal muscle feed arteries

PurposeWe tested the hypothesis that exposure to a short-duration (1xa0h) increase in intraluminal pressure, to mimic pressure associated with a bout of exercise, would attenuate age-induced impairments of vascular smooth muscle (VSM) constrictor responses in soleus muscle feed arteries (SFA) via the Rho pathway.MethodsSFA from young (4xa0months) and old (24xa0months) Fischer 344 rats were cannulated and pressurized to 90 or 130xa0cmH2O for 1xa0h. Following the 1-h treatment, pressure in P130 arteries was lowered to 90xa0cmH2O for examination of vasoconstrictor responses to norepinephrine (NE), angiotensin II (Ang II), and phenylephrine (PE). To assess the role of the Rho pathway, vasoconstrictor responses were assessed in the absence or presence of a RhoA-kinase inhibitor (Y27632) or RhoA-kinase activator (LPA).ResultsVasoconstrictor responses to NE, Ang II, and PE were impaired in old P90 SFA. Pretreatment of old SFA with increased pressure improved vasoconstrictor responses to NE, PE and Ang II. The beneficial effect of the pressure pretreatment in old SFA was eliminated in the presence of Y27632. In the presence of LPA, vasoconstrictor responses to Ang II were improved in old SFA such that responses were not different than young P90 SFA.ConclusionThese results indicate that a short-duration exposure to increased intraluminal pressure, to mimic pressure associated with a bout of exercise, attenuates or reverses the age-related decrement in VSM constrictor responses in SFA and that the beneficial response is mediated through Rho kinase.

Functional adaptation of bovine mesenteric lymphatic vessels to mesenteric venous hypertension

Lymph flow is the primary mechanism for returning interstitial fluid to the blood circulation. Currently, the adaptive response of lymphatic vessels to mesenteric venous hypertension is not known. This study sought to determine the functional responses of postnodal mesenteric lymphatic vessels. We surgically occluded bovine mesenteric veins to create mesenteric venous hypertension to elevate mesenteric lymph flow. Three days after surgery, postnodal mesenteric lymphatic vessels from mesenteric venous hypertension (MVH; n = 7) and sham surgery (Sham; n = 6) group animals were evaluated and compared. Contraction frequency (MVH: 2.98 ± 0.75 min(-1); Sham: 5.42 ± 0.81 min(-1)) and fractional pump flow (MVH: 1.14 ± 0.30 min(-1); Sham: 2.39 ± 0.32 min(-1)) were significantly lower in the venous occlusion group. These results indicate that postnodal mesenteric lymphatic vessels adapt to mesenteric venous hypertension by reducing intrinsic contractile activity.