Responses Of Mesenteric Arteries Research Articles

Fenofibrate increases neuronal vasoconstrictor response in mesenteric arteries from diabetic rats: Role of noradrenaline, neuronal nitric oxide and calcitonin gene-related peptide

We evaluated the possible effects of long-term fenofibrate treatment on adrenergic, nitrergic and CGRP-ergic innervation function in mesenteric arteries from streptotozin-induced diabetic rats. We analysed the vasoconstrictor response to electrical field stimulation (EFS) and the effects of the α antagonist phentolamine, the calcitonin gene related peptide (CGRP) receptor antagonist CGRP (8–37) and the nitric oxide synthase (NOS) inhibitor L-NAME in segments from untreated and fenofibrate-treated (100 mg/kg/day) diabetic rats. The vasomotor responses to noradrenaline (NA), CGRP and the NO donor sodium nitroprusside (SNP) were analysed, and NA, CGRP, and NO releases were measured. Neuronal NOS (nNOS), phosphorylated nNOS (P-nNOS), and RAMP1 protein expression were also analysed. Fenofibrate enhanced EFS-induced contractions. Phentolamine reduced EFS-induced contractions more in segments from fenofibrate-treated than in untreated rats. Fenofibrate increased vasoconstrictor response to NA and did not modify NA release. L-NAME increased EFS-induced contractions to a higher extent in segments from fenofibrate-treated than untreated rats. Fenofibrate did not change the vasodilator response to SNP but increased EFS-induced nitric oxide release. CGRP (8–37) increased EFS-induced contractions less in segments from fenofibrate-treated rats. Fenofibrate increased the vasodilator response to CGRP and reduced CGRP release. P-nNOS and RAMP1 expression were increased in segments from fenofibrate-treated rats, while nNOS expression remained unmodified. Fenofibrate enhances the vasoconstrictor response to EFS in diabetic rats. This effect is the functional result of the modifications of at least: (i) adrenergic function, enhanced by increased sensitivity to noradrenaline; (ii) nitrergic function, enhanced by increased neuronal NO release; and (iii) CGRP function, decreased by a reduction in CGRP release.

Shear Stress–dependent Effects of Lysophosphatidic Acid on Agonist-induced Vasomotor Responses in Rat Mesenteric Artery

We have previously shown that lysophosphatidic acid (LPA), a bioactive plasma lysophospholipid, markedly accelerates shear stress-induced Ca2+ responses in cultured vascular endothelial cells (ECs). This study aimed to demonstrate the impact of LPA and luminal shear stress on vasomotor regulation in the isolated rat mesenteric artery (MA) using a videomicroscopic technique. Although the addition of LPA to the perfusate in a concentration range of 0.03-0.3 μM had no significant effect on the basal MA tone, LPA in a similar concentration range led to increased phenylephrine-induced MA contraction and reduced acetylcholine-induced MA relaxation under physiological shear conditions. These vasomodulatory actions of LPA, which vanished upon removal of ECs, were positively dependent on luminal shear stress levels and were markedly inhibited by the LPA receptor antagonist Ki16425, the cyclooxygenase inhibitor indomethacin, and the thromboxane A2 receptor antagonist SQ29548. These data thus suggest that LPA can modify the agonist-induced vasomotor responses in MAs in a shear stress-dependent manner. This effect of LPA was mediated through ECs, the LPA receptor, and cyclooxygenase/thromboxane A2 signaling.

The effect of 1,1-dimethyl-4-phenyl-piperazinium on the response of mesenteric arteries to sympathetic nerve stimulation

Abstract The effect of 1,1-dimethyl-4-phenylpiperazinium (dmpp) on the response to sympathetic nerve stimulation of rat mesenteric arteries perfused with Tyrode solution at a constant flow has been studied. dmpp (0·3 μg/ml) infused for 3 min enhanced the vasoconstriction caused by stimulation. Infusion of the same concentration for 16–40 min greatly reduced the response to nerve stimulation but did not affect the vasoconstrictor response to injected noradrenaline. The blockade of the response to nerve stimulation produced by dmpp was overcome either by adding (+)-amphetamine to the perfusion fluid or by raising the calcium concentration. Neither effect of dmpp was altered by the infusion of atropine. These effects of dmpp were similar to those seen when acetylcholine was added to the perfusion fluid except that the effects of acetylcholine were diminished or abolished by a concentration of atropine much higher than that of acetylcholine. It is concluded that the receptors at the adrenergic nerve terminals are partly muscarinic and partly nicotinic.

Effect of hypoxia in mice mesenteric arteries surrounded by adipose tissue

To investigate the influence of hypoxia on the vasoactive effect of peri-vascular white adipose tissue. Isometric tension recordings were performed on mesenteric arteries from Swiss male mice with or without adherent adipose tissue. Hypoxia (bubbling with 95% N(2), 5% CO(2)) induced a biphasic response, i.e. vasoconstriction followed by vasorelaxation, in pre-contracted (noradrenaline, 10 μm) mesenteric arteries with adipose tissue in the presence of indomethacin (10 μm) and N(ω) -nitro-l-arginine (0.1 mm). Only a small vasorelaxation was observed in arteries without adipose tissue. Pre-contraction with 60 or 120 mm K(+) , incubation with tetraethylammoniumchloride (1 and 3 mm), apamin (1 μm) combined with charybdotoxin (0.1 μm) or 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) (10 μm) significantly impaired the hypoxic vasorelaxation. Removal of the endothelium only reduced the hypoxic vasorelaxation. Apamin (1 μm) and charybdotoxin (0.1 μm) did not influence the vasorelaxation of sodium hydrosulfide hydrate. Zinc protoporphyrin IX (10 μm), miconazole (10 μm), 8-(p-sulfophenyl)theophylline (0.1 mm), 1 H-[1, 2, 4]oxadiazolo[4,3- A]quinoxalin-1-one (10 μm), apocynin (0.3 mm), diphenyliodonium (1 μm), catalase (2500 U mL(-1)) and tempol (0.1 mm) did not influence the hypoxic vasorelaxation. In contrast to losartan (0.1 mm), indomethacin (10 μm) and SQ-29548 (10 μm) significantly reduced the hypoxic vasoconstriction. Moderate hypoxia induces a biphasic vasomotor response in mice mesenteric arteries surrounded by adipose tissue. The hypoxic vasoconstriction is endothelium independent, whereas the vasodilation is endothelium dependent, soluble guanylyl cyclase independent and in part mediated by opening K(Ca) channels. Cyclooxygenase metabolites mediate the hypoxic vasoconstriction, while endothelium-derived hyperpolarizing factor plays a small role in the hypoxic vasorelaxation.

Testosterone Increases Myogenic Reactivity of Second-Order Mesenteric Arteries in both Defective and Normal Androgen Receptor Adult Male Rats

Testosterone (T) and the androgen receptor (AR) are involved in mechanisms associated with hypertension and vessel reactivity. To investigate T and the AR on blood vessel reactivity, testicular feminized male (TFM; AR deficient males) and normal androgen receptor (NAR) male rats were used. Therefore, if the functional AR is necessary for plasma T to regulate vessel responsiveness, TFM males will exhibit altered vessel function compared to NAR males. Adult (16 weeks of age) TFM or NAR males were assigned to the following treatment groups: gonadal intact controls (CONT), castrate (CAST), or castrate with T replacement (CAST+T) with (n=8-10/group). Plasma T followed a consistent pattern with CAST+T elevated compared to CONT and CAST TFM and NAR males. In addition, CAST plasma T was significantly decreased compared to CONT and CAST+T in TFM and NAR males. In a similar manner for systolic blood pressure (SBP), CAST lowered SBP compared to CONT in both NAR and TFM. Following 8 weeks of treatment, second-order mesenteric artery responses to changes in intraluminal pressure (myogenic reactivity) were analyzed using a pressure arteriograph system. Both TFM (P < 0.05) and NAR (P < 0.05) CAST groups revealed a decrease in myogenic reactivity compared to CONT. Following T treatment the TFM CAST+T myogenic reactivity returned to CONT levels, whereas the NAR CAST+T myogenic reactivity increased a further 10%. The results of this study indicate that T differentially regulates mesenteric artery reactivity in TFM and NAR males. Our data also demonstrate that both AR and/or non-AR mediated mechanisms may partially contribute to SBP regulation.

Gender difference and change of α1-adrenoceptors in the distal mesenteric arteries of streptozotocin-induced diabetic rats

BackgroundThe purpose of this study was to evaluate the gender-related changes in the function and distribution of α1-adrenoceptors in the distal mesenteric artery of streptozotocin (STZ)-induced diabetic rats at the level of α1-adrenoceptor subtypes.MethodsDiabetes was induced by intravenous injection of STZ in a dose of 60 mg/kg through the tail vein in 8 week-old male or female Sprague-Dawley rats (n = 13/group). Age-matched normal rats (n = 15) were used as a control group. Four weeks after STZ injection, the change in mean arterial pressure caused by a 45° tilting was recorded. The α1-adrenoceptor subtypes mediating contractions of the distal mesenteric artery were investigated using the agonist, phenylephrine as well as subtype-selective antagonists including prazocin, 5-methylurapidil, and BMY 7378. The expression of α1-adrenoceptor subtypes of each artery was examined by immunofluorescence staining and western blotting using subtype selective antibodies.ResultsCompared with normal male rats, the contractile response to phenylephrine was decreased in the distal mesenteric artery in normal female rats. Moreover, a decrease in contractile force was observed in STZ-induced diabetic rats compared with age-matched controls. Western blotting revealed that there was the difference between normal male and female rats in manifestation of the α1D-adrenoceptor. In STZ-induced male and female diabetic rats, all α1-adrenoceptor subtypes were decreased in distal mesenteric arteries, compared with normal rats.ConclusionsThere was the gender-related functional difference of α1-adrenoceptors in normal rats. In both male and female rats, diabetes decreased the contractile response in mesenteric arteries, which might be caused by the overall change in α1-adrenoceptor.

Vasoconstrictor Potential of Coronary Aspirate From Patients Undergoing Stenting of Saphenous Vein Aortocoronary Bypass Grafts and Its Pharmacological Attenuation

Stent implantation into atherosclerotic plaques releases, apart from particulate debris, soluble substances that contribute to impaired microvascular perfusion. To quantify the release of vasoconstrictors and to determine the efficacy of coronary dilators to attenuate their action. Using a distal protection/aspiration device, coronary arterial blood was retrieved before and during stenting in 22 patients with severe saphenous vein aorto-coronary bypass stenoses. The release of catecholamines, endothelin, serotonin, thromboxane B(2), and tumor necrosis factor (TNF)α was measured. The response of rat mesenteric arteries with intact (+E) and denuded (-E) endothelium to aspirate plasma was normalized to that by KCl. Responses to selective receptor blockade, adenosine, nitroprusside, and verapamil against the aspirate-induced constriction were determined. The coronary arterial plasma withdrawn before stenting induced 21±5% and the aspirate plasma after stenting induced 95±8% of maximum KCl-induced vasoconstriction. Serotonin, thromboxane B(2), and TNFα release into aspirate plasma increased by 1.9±0.2 μmol/L, 25.6±3.1 pg/mL, and 19.7±6.1 pg/mL, respectively, during stenting. The aspirate-induced vasoconstriction was largely antagonized by selective serotonin receptor blockade, with little further antagonism by additional thromboxane receptor blockade. TNFα did not induce constriction per se but potentiated the constriction with serotonin and the thromboxane-analog U-46619 in arteries +E. The concentrations to induce half-maximal vasodilation were comparable for nitroprusside (+E, 3.3×10(-8); -E, 1.9×10(-8) mol/L) and verapamil (+E, 8.3×10(-8); -E, 7.8×10(-8) mol/L), and the vasoconstriction was eventually eliminated. The vasodilator response to adenosine was dependent on functional endothelium and weaker. Serotonin is the main coronary vasoconstrictor after stenting, and thromboxane and TNFα somewhat potentiate the serotonin response. Nitroprusside and verapamil are more potent than adenosine to attenuate the aspirate plasma-induced vasoconstriction, and they are not dependent on functional endothelium.

Dehydroepiandrosterone fatty acyl esters in high density lipoprotein: Interaction with human vascular endothelial cells and vascular responses ex vivo

Dehydroepiandrosterone (DHEA) fatty acyl esters once incorporated in high density lipoprotein (HDL) induce a stronger vasodilatory response in rat mesenteric arteries ex vivo compared to native HDL. We studied the role of HDL receptor, scavenger receptor class B, type 1 (SR-B1), as well as estrogen and androgen receptors in the vasodilatory response of HDL-associated DHEA fatty acyl esters. Using cultured human vascular endothelial cells (HUVEC), we investigated the possible internalization and cellular response of HDL-associated DHEA esters. We prepared DHEA ester-enriched HDL by incubating human plasma in the presence of DHEA. After isolation and purification, HDL was added in cumulative doses to arterial rings precontracted with noradrenaline. Inhibition of the function of SR-B1 almost completely abolished maximal vasorelaxation by DHEA-enriched HDL while estrogen or androgen receptor blockage had no significant effect. When HUVECs were incubated in the presence of [ 3H]DHEA ester-enriched HDL, the amount of intracellular [ 3H]-radioactivity increased steadily during 24 h. Blocking of SR-B1 reduced this uptake by a mean of 30%. The proportion of unesterified [ 3H]DHEA, as analyzed by thin-layer chromatography, increased intracellularly and in the cell culture media after several hours of incubation of the cells in the presence of [ 3H]DHEA ester-enriched HDL. This indicated slow hydrolysis of DHEA fatty acyl esters and subsequent excretion of unesterified DHEA by the cells. In conclusion, DHEA-enriched HDL induced vasorelaxation via the SR-B1-facilitated pathway. However, this vasodilation is not likely to be attributed to rapid hydrolysis of HDL-associated DHEA esters by the vascular endothelium.

Hypertension Induced by Episodic Reductions in Uteroplacental Blood Flow in Gravid Rat

Background. The etiology of preeclampsia remains unclear. Animal modeling of preeclampsia has been useful; however, no model to date represents episodic changes in uteroplacental blood flow that may occur in preeclampsia. Objective. To develop a gravid rat model characterized by episodic reductions in uteroplacental blood flow. Method. Pregnant Sprague Dawley rats were used and subjected to SHAM, reduced uterine perfusion pressure (RUPP), or aortic occlusion on gestational Day 14. Aortic occlusion surgery consisted of implantation of a silastic vascular occluder around the abdominal aorta and silver clips around the uterine–ovarian arteries. Aortic occlusion animals were subjected to five consecutive days of occlusion (40% reduction) each session lasting 1 h. On Day 21, maternal mean arterial pressure (MAP) and fetal morphology were assessed. For isolated blood vessels, resistance-sized mesenteric arteries were harvested and mounted on a pressure arteriograph. Result. Occluder animals experienced a 10 mmHg rise in MAP as compared to SHAM (p < 0.05), and RUPP MAP was significantly increased as compared to control subjects (p < 0.05). Pups from Occluder animals exhibited a decrease in fetal weight as compared to SHAM (p < 0.05), but an increase in fetal weight as compared to RUPP (p < 0.05). Myogenic reactivity of second-order mesenteric arteries increased in Occluder animals as compared to SHAM (p < 0.05), but were similar to that of RUPP. Conclusion. Episodic reductions in uteroplacental blood flow play a crucial role in the altered vascular reactivity seen in Occluder animals and may represent a new model to investigate the mechanisms associated with episodic reductions in uteroplacental blood flow in pathological pregnancies.

Increased Myogenic Responses of Resistance-Sized Mesenteric Arteries After Reduced Uterine Perfusion Pressure in Pregnant Rats

Objective. A central component of preeclampsia is a reduction in utero-placental perfusion. We tested the hypothesis that vascular reactivity of second – order mesenteric arteries would be increased in a pregnant rat with reduced uterine perfusion pressure (RUPP). Methods. Pregnant 10–12 week old Sprague-Dawley rats underwent RUPP surgery on gestational day 14, and experiments were carried out on day 20. SHAM operated animals were used as controls. Resistance caliber mesenteric arteries (200–250 μm) were isolated, myogenic reactivity and responses to vasoconstrictor and vasodilator agonists were assessed utilizing a pressurized arteriograph system. Results. RUPP resulted in maternal hypertension and reductions in fetal number and weight. Resistance caliber mesenteric arteries (200–250 μm) were isolated, myogenic reactivity and responses to vasoconstrictor and vasodilator agonists were assessed utilizing a pressurized arteriograph system. Myogenic reactivity responses were normalized as a percent change in vessel diameter from an initial diameter at 20 mmHg. The mesenteric arteries from RUPP animals exhibited a significant increase in myogenic reactivity compared to SHAM controls (p < 0.05). This increased myogenicity was reversed with prostaglandin inhibition, suggesting a role for a vasoconstrictor prostaglandin. In addition to alterations in myogenic reactivity, resistance-sized arteries from RUPP animals have decreased responses to nitric oxide (NO) as evidenced by decreases in responses to methacholine (ME; P < 0.05) and no change in myogenic reactivity after NO synthase blockade. Conclusion. RUPP alters the behavior of resistance caliber arteries to favor a more contractile phenotype with decreased in NO responses, which is similar to what is seen in preeclampsia.

Colony social stress differentially alters blood pressure and resistance-sized mesenteric artery reactivity in SHR/y and WKY male rats

Increased sympathetic nervous system (SNS) activity, testosterone, and spontaneously hypertensive rat Y chromosome (SHR Yc) play a role in a genetic model of hypertension. Male rats with the SHR Yc and Wistar-Kyoto (WKY) autosomes (denoted SHR/y) exhibit these characteristics when compared to rats with the WKY Yc and WKY autosomes (denoted WKY). We hypothesized that chronic social stress will increase blood pressure and SNS activity more in SHR/y males compared to WKY males, resulting in increased myogenic reactivity along with decreased vasoconstriction of small mesenteric arteries. SHR/y and WKY males were housed in strain- specific colonies (10 males with 10 females) or as controls (10 males). Systolic blood pressure (SBP) and blood samples were collected prior to termination. Second-order mesenteric arteries were studied using a pressure arteriograph in which myogenic reactivity and phenylephrine (PE) responsiveness were measured. SHR/y colony SBP, and circulating norepinephrine and testosterone concentrations were elevated compared to control and WKY colony males (p < 0.05). Mesenteric artery myogenic reactivity was increased in SHR/y colony males (p < 0.001). Mesenteric arteries from SHR/y colony males exhibited a significant decrease in PE-induced constriction. Colony social stress elevated both SNS activity and testosterone level which may be responsible for the increased mesenteric artery myogenic reactivity, and SBP as noted in SHR/y males.

Deleterious combined effects of salt-loading and endothelial cell restricted endothelin-1 overexpression on blood pressure and vascular function in mice

We previously showed that young transgenic mice overexpressing preproendothelin-1 specifically in endothelial cells had hypertrophic remodeling, endothelial dysfunction, increased vascular NADPH oxidase activity, and inflammation in mesenteric small arteries without blood pressure (BP) elevation compared to nontransgenic wild-type littermates. To assess the consequences of salt-loading and the role of endothelin receptors, we investigated the effects of these on vascular structure, function, and oxidative stress in mesenteric arteries in salt-loaded transgenic mice treated with endothelin receptor antagonists. Ten-month-old male transgenic and wild-type littermates were salt-loaded (4% NaCl) and treated with endothelin subtype A receptor antagonist (ET(A)RA, ABT-627, 5 mg/kg per day), endothelin subtype B receptor antagonist (ET(B)RA; A-192621, 30 mg/kg per day), or ET(A)/BRA (bosentan, 100 mg/kg per day) for 4 weeks. BP was measured by radiotelemetry, vascular reactivity of mesenteric small arteries was studied on a pressurized myograph, and vascular NADPH oxidase activity was studied by lucigenin chemiluminescence. Transgenic+salt mice had significantly increased BP compared with wild-type+salt mice, which was prevented by ET(A)RA and dual ET(A/B)RA but further increased by ETB antagonism. Increased small artery media/lumen ratio of transgenic+salt mice was significantly decreased only by dual ET(A/B)RA (P < 0.01), whereas no differences were found in media cross-sectional area. Impaired maximal relaxation of small arteries to acetylcholine was significantly prevented with ET(A)RA and ET(A/B)RA (P < 0.05). N(omega)-nitro-L-arginine methyl ester-induced reduction of acetylcholine maximal relaxation was partially prevented by ET(A)RA, completely prevented by dual, and partially restored by vitamin C preincubation following dual ET(A/B)RA. The blunted endothelin-1 contractile response of small arteries found in transgenic+salt mice was partially restored by ET(A)RA and completely prevented by dual ET(A/B)R antagonism. The vasoconstrictor response to endothelin-1 was not altered in the presence or absence of ET(B)RA. Increased vascular NADPH oxidase activity of transgenic+salt mice was further increased by ET(B)RA but returned to levels seen in wild-type+salt mice under either ET(A)RA and ET(A/B)RA. Transgenic+salt mice with endothelin-1 overexpression have structural alterations of mesenteric resistance vessels, endothelial dysfunction due to reduced nitric oxide bioavailability, a reduced responsiveness to endothelin-1, and enhanced vascular NADPH oxidase activity. ET(B)RA further exacerbated these effects, whereas ET(A)RA significantly improved but did not normalize them in chronically salt-loaded transgenic mice with endothelial cell human endothelin-1 overexpression. Salt and endothelin-1 overexpression have deleterious additive effects on vascular remodeling mediated by ET(A)R and ET(B)R. ET(B)R probably located in the endothelium, however, also exerts beneficial effects on endothelial function in this experimental paradigm. The present study provides the first in-vivo demonstration that endothelin-1 overexpression when associated with high-salt intake results in enhanced endothelial dysfunction and vascular remodeling of resistance vessels, and contributes to elevated BP, via ET(A)R and ET(B)R.

Vascular hypertrophy-associated hypertension of profilin1 transgenic mouse model leads to functional remodeling of peripheral arteries

Increased mechanical stress/hypertension in the vessel wall triggers the hypertrophic signaling pathway, resulting in structural remodeling of vasculature. Vascular hypertrophy of resistance vessels leads to reduced compliance and elevation of blood pressure. We showed before that increased expression of profilin1 protein in the medial layer of the aorta induces stress fiber formation, triggering the hypertrophic signaling resulting in vascular hypertrophy and, ultimately, hypertension in older mice. Our hypothesis is that profilin1 induced vascular hypertrophy in resistance vessels, which led to elevation of blood pressure, both of which contributed to the modulation of vascular function. Our results showed significant increases in the expression of alpha(1)- and beta(1)-integrins (280 + or - 6.3 and 325 + or - 7.4%, respectively) and the activation of the Rho/Rho-associated kinase (ROCK) II pathway (260 and 350%, respectively, P < 0.05) in profilin1 mesenteric arteries. The activation of Rho/ROCK led to the inhibition of endothelial nitric oxide synthase expression (39 + or - 5.4%; P < 0.05) and phosphorylation (35 + or - 4.5%; P < 0.05) but also an increase in myosin light chain 20 phosphorylation (372%, P < 0.05). There were also increases in hypertrophic signaling pathways in the mesenteric arteries of profilin1 mice such as phospho-extracellular signal-regulated kinase 1/2 and phospho-c-Jun NH(2)-terminal kinase (312.15 and 232.5%, respectively, P < 0.05). Functional analyses of mesenteric arteries toward the vasoactive drugs were assessed using wire-myograph and showed significant increases in the vascular responses of profilin1 mesenteric arteries toward phenylephrine, but significant decreases in response toward ROCK inhibitor Y-27632, ACh, sodium nitrite, and cytochalasin D. The changes in vascular responses in the mesenteric arteries of profilin1 mice are due to vascular hypertrophy and the elevation of blood pressure in the profilin1 transgenic mice.

Uncoupling Protein 2 Ablation Exacerbates High-Salt Intake-Induced Vascular Dysfunction

Salt-induced vascular dysfunction in which underlying mechanisms involve reactive oxygen species (ROS)-mediated reduction of nitric oxide (NO) bioavailability has been well documented. Uncoupling protein 2 (UCP2) has been implicated in the vascular protection, specifically by decreasing ROS production. However, it is unclear how UCP2 affects vascular function in salt-loaded mice. UCP2-deficient (UCP2(-/-)) and wild-type (WT) mice were placed on either a normal-salt (NS, 0.5%) or a high-salt (HS, 8%) diet for 24 weeks. Blood pressure (BP), mesenteric arterial reactivity, superoxide production, and NO bioavailability in the intact vessels were measured in each group. UCP2(-/-) mice on a HS diet had a higher BP than those on a NS diet (P < 0.01). However, BP in WT mice was not different between the NS and HS diet group. Phenylephrine (PE)-induced contraction was enhanced while acetylcholine (ACh)-elicited relaxation was impaired in mesenteric resistance arteries from the HS diet-fed WT mice. Importantly, the enhanced contraction and impaired relaxation were both further exacerbated in UCP2(-/-) mice. Similarly, the HS diet led to a moderate increase in superoxide production and a comparable decrease in NO availability in both aortas and mesenteric resistance vessels, and these effects were also remarkably enhanced in UCP2(-/-) mice. These findings suggest that UCP2 plays an important role in preventing salt-sensitive hypertension, which may be achieved by suppressing superoxide production and reserving NO bioavailability in blood vessels.

Beneficial Effects of Activation of PKC on Hemorrhagic Shock in Rats

The reduced vascular reactivity after severe trauma or shock played an important role in the development and outcome of shock. Our previous study showed that protein kinase C (PKC) took part in the regulation of vascular reactivity after hemorrhagic shock. The objective of this study was to investigate the protective effects of activation of PKC on hemorrhagic shock and its related mechanism. Sprague dawley rats were subjected to hemorrhagic shock (40 mm Hg for 2 hours). Effects of the PKC agonist, phorbol-12-myristate-13-acetate (PMA), and its inhibitor, staurosporine, on hemodynamic parameters were observed in vivo or in vitro. The hemodynamic parameters included mean arterial blood pressure, left intraventricular systolic pressure, the maximal change rate of left intraventricular pressure (+/-dp/dtmax), blood gases including pH, Po2, Sao2, and base excess, animal survival time, the vascular reactivity and calcium sensitivity of superior mesenteric artery, and mitochondrial function and blood flow of liver and kidney. Intravenous administration of PKC agonist, PMA, at the concentration of 1 microg/kg significantly increased the mean arterial blood pressure, left intraventricular systolic pressure, +/-dp/dtmax, the pressor effect, and the contractile response of norepinephrine, it also improved the blood gases, and prolonged the survival time of shocked rats. In addition, the intravenous administration of PMA improved mitochondrial function and liver and kidney blood flow. A total of 10(-7) mol/L of PMA administrated in vitro significantly improved the vascular reactivity and calcium sensitivity of superior mesenteric artery to norepinephrine and Ca2+. These effects of PMA were abolished by the PKC specific inhibitor staurosporine (1 microg/kg in vivo or 10(-7) mol/L in vitro). Activation of PKC has protective effects on hemorrhagic shock. The mechanism is related not only to its hemodynamic stabilization effect via improving vascular reactivity and calcium sensitivity but also to its effect on improving the perfusion and mitochondrial function of vital organs.

Effect Of PPADS On Mesenteric Arterial And Portal Venous Flow Responses To Splanchnic Nerve Stimulation

Our previous work suggested that splanchnic nerve stimulation may exert differential effects on mesenteric arterial and portal venous hemodynamics. This study tested the hypothesis that ATP contributes to the differences in mesenteric arterial and portal venous responses to splanchnic nerve stimulation.Spontaneously hypertensive rats (SHR) were anesthetized with urethane/chloralose and fitted with catheters to record arterial pressure. The rats were also instrumented for splanchnic nerve stimulation and for mesenteric arterial and portal venous blood flow recording. Frequency response curves (1–15 Hz) were constructed before and after treatment with pyridoxal‐phosphate‐6‐azophenyl‐2′,4′‐disulfonate (PPADS; 20 mg/kg), an ATP P2X receptor antagonist.Splanchnic nerve stimulation caused frequency dependent decreases in mesenteric arterial and portal venous blood flow. Treatment with PPADS caused a rightward displacement of the frequency response curves for both mesenteric arterial flow and portal venous flow. The magnitude of this displacement was less than that observed following omega conotoxin treatment.Collectively, these data suggest that ATP contributes to both mesenteric arterial and portal venous responses to splanchnic nerve stimulation. Supported by NIH #2RO1HL63053‐ARRA (DM) and USD SSOM bridge funds.

Salt‐Induced Increase in 20‐HETE Production Alters Vascular Function of Mesenteric Resistance Arteries of Dahl Salt‐Sensitive Rats

Cytochrome P450‐4A ω‐hydroxylase (CYP4A) enzymes and their metabolite, 20‐hydroxyeicosatetraenoic acid (20‐HETE) are potential contributors to inflammation and vascular alterations with elevated dietary salt and/or hypertension. This study evaluated the role of the 20‐HETE/CYP4A system in modulating salt‐induced changes in vascular reactivity in mesenteric resistance arteries from Dahl salt‐sensitive (SS) rats. High salt (HS; 4% NaCl) diet increased expression of mRNA for the 4A3 and 4A8 isoforms of CYP4A and increased 20‐HETE production by ~25% in mesenteric arteries of SS rats. In SS rats fed HS diet, CYP4A enzyme inhibition with dibromododecenyl methylsulfimide (DDMS) [30–50 μM]: 1) reduced norepinephrine sensitivity; 2) rescued impaired dilation in response to reduced PO2; 3) switched the mechanism of hypoxic dilation from cyclooxygenase products to NO; and 4) selectively augmented vasodilation to the NO donor DETA NONOate. The 20‐HETE agonist 20‐OH‐5,14 HEDE (WIT003) [1μM] restored norepinephrine sensitivity and attenuated the restoration of hypoxic dilation in DDMS‐treated vessels of salt‐fed rats. These results suggest that the 20‐HETE/CYP4A system modulates both norepinephrine and NO sensitivity, suppresses hypoxic dilation, and could contribute to vascular inflammation and increased vascular resistance during the early stage of salt‐sensitive hypertension. (NIH #HL65289, #HL72920, #HL92026; #DK‐38226).

Increased Myogenic Reactivity of Resistance‐sized Mesenteric Arteries from Pregnant Rats with Episodic Reductions in Uteroplacental Perfusion

Pregnancy is associated with increased placental blood flow (BF) to the developing fetus. A central component of preeclampsia is thought to be a reduction in placental BF leading to altered vascular reactivity. It is suggested that short term elevations in blood pressure may lead to periodic reductions in uteroplacental blood flow (UBF) and this may play a role in preeclampsia. The purpose of this study was to develop a gravid rat model characterized by episodic reductions in UBF to elucidate the role of periodic decreases in UBF on vascular reactivity. We used pregnant Sprague Dawley rats and subjected them to Sham or aortic occlusion surgery on Day 14 of gestation. Aortic occlusion surgery consisted of implantation of a silastic vascular occluder around the abdominal aorta along with silver clips (0.106mm ID) around the uterine‐ovarian arteries. Aortic occlusion animals were subjected to 5 days of reduced UBF (40% reduction) for 1 hour each session. On Day 21, second order mesenteric arteries were mounted on a pressurized arteriograph. Myogenic reactivity of small mesenteric arteries was increased in Occluder animals compared to Sham (p&lt;0.05). This data suggest that episodic reductions in UBF may mimic some of the characteristics of preeclampsia including altered vascular reactivity toward a constrictive phenotype. Aortic occlusion may be a new model for investigating mechanisms associated with reduced UBF.

Arterial Function and Flow Related Arterial Remodeling during DOCA‐salt Hypertension

HypothesisThe DOCA‐salt Hypertensive rat (DOCA), a model of enhanced function of endothelin‐1 (ET‐1), displays: 1. Increased importance of endogenous ET‐1 in vasoreactivity 2. Altered flow‐related arterial remodeling.Methods1. 2nd order rat mesenteric artery (MrA) reactivity was assessed using wire‐myography. 2. Flow modifying surgery was performed as described by Pourageaud and De Mey (1997) and arteries were analysed by pressure arteriography and histology.Results1. the endothelin‐receptor antagonist Bosentan endothelium‐dependently reduced contractile responses to K+‐induced depolarization in arteries of DOCA but not SHAM. 2. No outward hypertrophic remodeling occurred in high flow (HF) arteries of DOCA. Arteries exposed to low flow (LF) conditions, showed inward remodeling, hypertrophy, and infiltration of ED‐1 (monocyte/macrophage‐marker) positive cells. DOCA MrA's showed a marked reduction in calculated distensibility. α‐Smooth muscle actin staining of LF vessels showed development of “collaterals” in the adventitia.ConclusionDOCA MrA's show increased contribution of endogenous ET‐1 to K+‐induced vasomotor responses, impaired outward remodeling, arterial stiffening and hypertrophy. LF MrA's show infiltration of inflammatory cells and development of “collaterals” in the adventitia.This study was performed within project T2–108 of the Dutch Top Institute Pharma.

Attenuated endothelin‐1 (ET‐1) vasoconstrictor responses in cardiometabolic syndrome are attributed to increased ET‐B receptors

Vascular dysfunction is an important complication linking cardiometabolic syndrome with cardiovascular diseases. The objective of the present study was to discover the effect of ET‐1 on mesenteric resistance arteries from a cardiometabolic syndrome disease model and assess the relative contribution of ET‐A and ET‐B receptors. Spontaneously hypertensive obese (SHROB) rats displayed increased blood pressure (154±3 vs. 123±2 mmHg) and body weight (417±7 vs. 270±5 g) compared to WKY rats. Mesenteric arteries were isolated and diameter responses to the vasoconstrictor peptide ET‐1 (0.01–10nM) were determined. Baseline mesenteric resistance artery diameters did not differ between WKY, SHR and SHROB. Mesenteric resistance artery responses to 10 nM ET‐1 were greatly attenuated in SHROB (26±9%) compared to SHR (44±13%) and WKY (69±2%). Addition of either ET‐A antagonist BQ123, or ET‐B agonist sarafotoxin 6c resulted in vasodilation in SHROB (105±2% and 104±2%, respectively) suggesting an enhanced ET‐B receptor mediated response in SHROB. Furthermore, ET‐B receptor protein expression was elevated 32 fold in SHROB compared to WKY, respectively. These results indicate that upregulation of the ET‐B receptor contributes to the greatly diminished ET‐1 vasoconstriction in cardiometabolic syndrome.