Axl mediates vascular remodeling induced by deoxycorticosterone acetate-salt hypertension

Axl, a receptor tyrosine kinase, was recently identified as a novel candidate gene in a genetic model of salt-sensitive hypertension (Sabra rat). Our group first reported that Axl plays a significant role in vascular remodeling in response to injury. Here we investigated the role of Axl in the pathogenesis of hypertension in a deoxycorticosterone acetate (DOCA)-salt model. Hypertension was induced in Axl wild-type (Axl(+/+)) mice and Axl-deficient (Axl(-/-)) mice by uninephrectomy and DOCA-salt for 6 weeks. Controls were uninephrectomized and received tap water and regular chow ad libitum. DOCA-salt treatment increased systolic blood pressure by 25 mm Hg in both genotypes after 1 week. Systolic blood pressure remained significantly elevated in Axl(+/+) DOCA, whereas systolic blood pressure levels in Axl(-/-) DOCA mice were the same as controls at 6 weeks. DOCA-salt increased relative kidney weight and glomerular hypertrophy by 40% compared with controls in both genotypes. Consistent with levels of systolic blood pressure, endothelium-dependent vasorelaxation was impaired in Axl(+/+) DOCA mice compared with Axl(+/+) controls, whereas in Axl(-/-) DOCA mice relaxation responses were similar to Axl(-/-) controls. In addition, endothelium-independent vasorelaxation was improved in Axl(-/-) DOCA mice compared with Axl(+/+) DOCA mice. Nitrotyrosine and phospho-Akt immunoreactivity was significantly reduced in arteries from Axl(-/-) DOCA mice compared with Axl(+/+) DOCA mice. The remodeling index of the mesenteric artery (media:lumen ratio) was significantly increased in Axl(+/+) DOCA mice compared with Axl(-/-) DOCA mice. Finally, increased vascular apoptosis in the Axl(-/-) DOCA mice suggests a likely mechanism for Axl-dependent effects on hypertension. These data strengthen the pathogenic role for Axl in salt-sensitive hypertension.     

Altered coronary dilation in deoxycorticosterone acetate-salt hypertension

OBJECTIVE: To compare coronary dilation in uninephrectomized hypertensive deoxycorticosterone acetate (DOCA)-salt rats (HTRs), treated for 2 or 4 weeks, with age-matched uninephrectomized normotensive rats (NTRs). DESIGN AND METHODS Coronary perfusion pressure was recorded in isolated hearts perfused at a constant flow rate to evaluate coronary resistance. RESULT: A decreased vasoconstriction due to NG-nitro-Larginine (NNLA, 30 pmol/I) in hearts from HTRs suggested a reduced basal nitric oxide (NO) release. In contrast, coronary vasodilation due to the NO donor, sodium nitroprusside (3 pmol/I), remained unaffected in 2-week HTRs, and was enhanced in 4-week HTRs. Cumulative dose-response curves to bradykinin induced an important vasodilation in NTRs, with a maximal response that remained unaffected in the presence of either NNLA (30 pmol/I), indomethacin (10 pmol/l) or the two combined. In contrast, hearts from HTRs showed a diminished maximal relaxation to bradykinin, suggesting an altered endothelium-dependent relaxation. The presence of NNLA or indomethacin had no effect on the weak relaxation observed in HTRs. However, NNLA and indomethacin combined unmasked an important relaxation due to bradykinin in HTRs. The addition of clotrimazole (1 pmol/I) to NNLA and indomethacin blunted the relaxation due to bradykinin in both NTRs and HTRs. Perfusion with superoxide dismutase (120 IU/ml) restored most of the coronary relaxation due to bradykinin in hearts from HTRs. Bradykinin-induced prostaglandin 12 (PGI2) and E2 (PGE2) production was unaffected by hypertension. No increase in thromboxane A2 (TXA2) due to bradykinin was detected. Finally, reduced reactivity to papaverine and forskolin was observed in hearts from HTRs. CONCLUSION: DOCA-salt hypertension is associated with alterations in coronary reactivity. Basal NO formation appears to be reduced in HTRs, but the intact relaxation to exogenous NO suggests a preserved guanylate cyclase pathway. In addition, alteration in adenylate cyclase activity, and not in prostaglandin production, may explain the blunted cAMP-mediated responses in HTRs. The combined nitric-oxide synthase (NOS) and cyclo-oxygenase (COX) inhibition unmasked an endothelium-derived hyperpolarizing factor (EDHF) involvement in the coronary dilation due to bradykinin in hearts from HTRs, suggesting that endothelial NO and PGI2, although unable to induce coronary smooth-muscle relaxation, can inhibit EDHF production in HTRs. Impairment in the adenylate cyclase pathway and the suppression of NO by free radicals may explain the blunted vasodilation in DOCA-salt hypertension.     

The role of chloride on deoxycorticosterone acetate-salt hypertension

Selective sodium loading attenuated the development of hypertension in the deoxycorticosterone acetate (DOCA) treated rat. The DOCA treated rat fed a diet equimolar in sodium to a 7% sodium chloride diet and in chloride to a standard diet, differed in various parameters from the DOCA treated rat fed a 7% sodium chloride diet: it had higher sodium concentration in both erythrocytes and muscles, a higher erythrocyte ouabain sensitive 22Na efflux rate constant (Kos), and a lower norepinephrine turnover rate in the heart and the spleen. These results suggest that the suppressed sympathetic nervous system activity and the activated cell membrane sodium pump contribute in part to the mechanism for the suppression of the development of hypertension in the DOCA-selective sodium loaded rat.     

Regulation of vasopressin receptors in deoxycorticosterone acetate-salt hypertension.

Since arginine vasopressin may play a role in mineralocorticoid hypertension, we examined the effects of deoxycorticosterone acetate (DOCA)-salt on vasopressin V1 and V2 receptor binding and their second messengers, inositol phosphate and adenylate cyclase, respectively, in liver and kidney to determine whether altered vasopressin receptor binding is pathogenetic in mineralocorticoid hypertension. The mean arterial blood pressure of mineralocorticoid (DOCA-salt)-treated rats (163 +/- 1 mm Hg) was increased compared with control salt-treated rats (salt) (122 +/- 1 mm Hg) and water-treated rats (120 +/- 1 mm Hg; p less than 0.001). Mineralocorticoid treatment also increased plasma sodium, osmolality, and vasopressin concentration (p less than 0.001). In the hypertensive animals, there was a reduction in hepatic V1 (DOCA-salt, 91 +/- 12; salt, 132 +/- 13; and water, 145 +/- 13 fmol/mg protein; p less than 0.05) and renal V2 receptor binding density (DOCA-salt, 53 +/- 5; salt, 93 +/- 9; and water, 95 +/- 9 fmol/mg protein; p less than 0.01), although receptor affinities remained unaltered. In contrast, the density of renal V1 receptors was increased by mineralocorticoid treatment (DOCA-salt, 24 +/- 2; salt, 16 +/- 2; water, 18 +/- 1 fmol/mg protein; p less than 0.05), although the affinity was unchanged. Downregulation of V2 receptors was associated with a decrease in maximum cyclic adenosine monophosphate levels (DOCA-salt, 19 +/- 4; salt, 49 +/- 6; water, 53 +/- 9 pmol.mg protein-1.10 min-1; p less than 0.05), whereas changes in V1 receptor levels were not associated with changes in maximum inositol phosphate levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gene transfer of endothelial NO synthase and manganese superoxide dismutase on arterial vascular cell adhesion molecule-1 expression and superoxide production in deoxycorticosterone acetate-salt hypertension

Enhanced vascular cell adhesion molecule-1 (VCAM-1) expression directly contributes to vascular dysfunction in hypertension. Decreased NO and/or increased superoxide are causative factors for such an event in the vessel wall. The present study was undertaken to determine whether gene transfer of endothelial NO synthase (eNOS) or manganese superoxide dismutase (MnSOD) affects VCAM-1 levels in arteries from hypertensive rats. Isolated carotid and femoral arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats were transduced for 4 hours with adenoviral vectors encoding eNOS, MnSOD, or beta-galactosidase reporter genes. Recombinant eNOS or MnSOD expression was evident morphologically and quantitatively 24 hours after gene transfer. Immunohistochemistry, ELISA, and Western blot techniques were used to determine VCAM-1 expression and levels. In addition, endogenous eNOS and MnSOD and in situ superoxide levels were analyzed by immunoblotting and fluorescence confocal microscopy, respectively. Arterial VCAM-1 expression was significantly higher in DOCA-salt hypertensive rats than in sham-operated rats; this expression was accompanied by decreased MnSOD but unaltered endogenous eNOS levels. VCAM-1 expression was significantly lower in MnSOD- and eNOS-transduced hypertensive arteries, with a concomitant reduction of superoxide level. These results suggest that gene transfer of MnSOD or eNOS suppresses arterial VCAM-1 expression in DOCA-salt hypertension by reducing the superoxide level.     

Left ventricular structure and performance in middle-aged rats with deoxycorticosterone acetate-salt hypertension

We designed this study to establish the structural and functional characteristics of the hypertrophied left ventricle of middle-aged rats during mineralocorticoid-salt hypertension. Treatment was initiated at 12 months of age, and the rats were studied at either 13 or 15 months of age (after 1 or 3 months of treatment). All rats were unilaterally nephrectomized. One group received deoxycorticosterone acetate (DOCA) injections (30 mg/kg s.c.) biweekly and 1% NaCl drinking water (DOCA salt), and the other group was injected with the vehicle (sesame seed oil) and given tap water to drink (sham). During the first 4 weeks of DOCA-salt treatment, arterial pressure reached its peak and left ventricular enlargement was mainly due to increases of 47% in cardiocyte cross-sectional area in the middle layer of the left ventricular wall. The last 2 months were characterized by an accelerated endomyocardial growth. Because absolute left ventricular mass did not increase during the last 2 months of treatment, we conclude that cellular hypertrophy was accompanied by a focal loss of cardiocytes. Myocardial hydroxyproline concentration was initially elevated by 37% but normalized by the third month of treatment. Intracellularly, myofibril volume percent was not changed, but mitochondria volume percent declined (13% in the midmyocardium and 15% in the endomyocardium) and sarcoplasmic volume density increased by 25% and 39%, respectively, in these regions. Left ventricular hypertrophy was associated with enhanced peak cardiac and stroke indexes, measured during increased preload, after both 1 and 3 months of DOCA-salt treatment. Acceleration of flow, however, was depressed in the rats with left ventricular hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Polyamines, vascular smooth muscle, and deoxycorticosterone acetate-salt hypertension

This study was performed to determine if an alteration in vascular polyamine contents is associated with the development of deoxycorticosterone acetate-salt hypertension. The effects of chronic administration of alpha-difluoromethylornithine, a specific irreversible inhibitor of ornithine decarboxylase and thus polyamine biosynthesis, on vascular polyamine contents, structure, and function as well as the development of hypertension was studied. Control and deoxycorticosterone acetate-salt rats received either tap water or a drinking solution containing alpha-difluoromethylornithine for 6 weeks, during which period systolic blood pressures were recorded. Vascular reactivity studies were performed on rings of aorta and tail artery. Medial thickness, vessel weight, and vascular polyamine contents were also assessed in these arteries. alpha-difluoromethylornithine treatment had no significant effect on either systolic blood pressure or vascular structure, function, and polyamine contents of control animals. The elevation in blood pressure and the increase in medial thickness, ring weight, and vascular polyamine contents as well as altered vascular reactivity observed in deoxycorticosterone acetate-salt rats was significantly attenuated by alpha-difluoromethylornithine treatment. These results are the first to demonstrate that vascular polyamine contents are elevated in the deoxycorticosterone acetate-salt rat and that chronic alpha-difluoromethylornithine treatment prevents the rise in vascular polyamines as well as the elevation in blood pressure and attendant changes in the vasculature. Thus, the increase in vascular polyamines may comprise a critical link between the initiating stimuli and the alterations in vascular structure and function implicated in the pathogenesis of deoxycorticosterone acetate-salt hypertension.     

Impaired vasomotor function induced by the combination of hypertension and hypercholesterolemia

Although it is well known that endothelial function is compromised in the presence of either hypertension (HTN) or hypercholesterolemia (HCh), less is known about whether and how the combination of these risk factors (HTN+HCh) results in impaired endothelium-dependent dilation (EDD). The aims of this study were to evaluate the influence of HTN+HCh on vasomotor function and to identify the mechanisms that underlie the altered vascular reactivity elicited by HTN+HCh. Endothelium-dependent and -independent vasomotor responses of aortic vessels were studied in mice with diet-induced HCh and/or HTN induced by chronic administration of either angiotensin II (AngII) or deoxycorticosterone acetate-salt. HTN+HCh elicited an impairment of EDD that appeared between each risk factor alone. Incubation with catalase resulted in more severe EDD impairment. Each risk factor enhanced vascular H₂O₂ production, but a larger response was noted with HTN+HCh. An attenuated EDD was not observed in AngII type 1a receptor deficient (AT1r^?/?) mice, but AT1r^?/? bone marrow chimeras exhibited more profound impairment compared with wild-type. HTN+HCh does not exert an additive effect of vasomotor dysfunction compared with either risk factor alone, and both H₂O₂ and blood cell–associated AT1r contribute to the impaired EDD responses in mice with HTN+HCh.     

Serotonin-induced contraction in mesenteric resistance arteries: signaling and changes in deoxycorticosterone acetate-salt hypertension

Large arteries from hypertensive subjects are hyperresponsiveness to 5-hydroxytryptamine (5-HT). We tested the hypothesis that small arteries (225 micro ID) have a profile similar to conduit arteries, including signal transduction mechanisms and the 5-HT receptor subtype(s) mediating arterial contraction in normal and high blood pressure. Aorta and mesenteric arteries from Sprague-Dawley (232+/-6 micro ID), sham (229+/-7 micro ID; systolic blood pressure, 120+/-2 mm Hg), or deoxycorticosterone acetate (DOCA)-salt rats (255+/-11 micro ID, 192+/-8 mm Hg) were mounted in a wire-based myograph. In resistance arteries from Sprague-Dawley rats, the 5-HT2A receptor mediated contraction; agonists of the 5-HT1B, 5-HT1D, 5-HT1F, and 5-HT2B receptor were inactive. The tyrosine kinase inhibitor genistein (5 micromol/L, 4.8-fold rightward shift), PD 098,059 (10 micromol/L, 3.2-fold shift), phospholipase C inhibitor NCDC (100 micromol/L), and nifedipine (50 nmol/L) reduced maximum 5-HT-induced contraction in small arteries (4.5% and 53% control, respectively). As in aorta, 5-HT had a decrease in threshold (100-fold lower), increase in potency (11.6-fold leftward shift), and increase in efficacy (140% sham response) in small arteries from DOCA-salt rats compared with sham. Unlike in aorta, 5-HT-induced contraction in DOCA-salt small arteries was shifted competitively by the 5-HT2A receptor antagonist ketanserin (-log K(B) [mol/L] for both sham and DOCA-salt, 9.25+/-0.1), and contraction to the 5-HT2B agonist BW723C86 was not observed. Thus, the 5-HT2A receptor remains the contractile receptor in hypertension in small arteries. Although similarities were observed for large and small arteries, differences under the condition of DOCA-salt hypertension exist that may determine serotonergic compounds effective in lowering blood pressure.     

Chronic V2 vasopressin receptor stimulation increases basal blood pressure and exacerbates deoxycorticosterone acetate-salt hypertension

The present study was intended to determine whether the long-term V2 receptor-mediated effects of vasopressin on sodium reabsorption in the renal collecting duct is an aggravating factor in salt-sensitive hypertension. Deoxycorticosterone acetate (DOCA)-salt hypertension was induced in uninephrectomized rats that had been chronically pretreated with a V2 agonist (dDAVP; 1-deamino-8D-arginine vasopressin; 0.6 microg/kg.d) or a V2 antagonist (SR121463, 3 mg/kg.d) or were untreated. Plasma osmolality and natremia were not significantly different in the groups. Blood pressure was significantly increased by dDAVP pretreatment (+11 mm Hg; P = 0.006), and this effect was exacerbated after DOCA-salt-induced hypertension (+17 mm Hg; P = 0.042). The dDAVP-treated rats had a lower hematocrit (40 +/- 2% vs. 47 +/- 1% and 45 +/- 2%) and markedly higher albuminuria (91 +/- 9 vs. 17 +/- 8 and 15 +/- 8 mg/d), mortality rate (50% vs. 0% and 0%), and cardiac and renal hypertrophy than the control and SR121463 groups. Histological renal lesions were worsened by V2 agonism and prevented by V2 antagonism. Renal mRNA expression of beta- and gamma-subunits of the epithelial sodium channel was significantly increased by dDAVP treatment (P < 0.05). These findings provide evidence that chronic stimulation of vasopressin V2 receptor raises basal blood pressure in rats and exacerbates the development of DOCA-salt hypertension, organ damage, and mortality. These effects could be due at least in part to the sustained stimulation of sodium reabsorption by epithelial sodium channel in the distal part of the nephron, which promotes sodium retention.     

Microvascular responses to endothelin in deoxycorticosterone acetate-salt hypertensive rats

The objective of the present study was to determine if endothelin-1 played a role in the elevated peripheral resistance in deoxycorticosterone-acetate (DOCA)-salt hypertension. Radioimmunoassay showed that the concentration of endothelin-1 was higher in thoracic aorta of the DOCA-salt group than that of the control normotensive (CN) group. Responses of arterioles in the rat cremaster to endothelin-1 were also observed using in vivo closed circuit television microscopy. Microvascular sensitivity to endothelin-1 was decreased in the DOCA-salt group. In the presence of an endothelin type A (ET-A) receptor antagonist, low concentrations of endothelin-1 induced a significant vasoconstriction in the DOCA-salt group. In the presence of endothelin type B (ET-B) receptor antagonist, microvascular responses to endothelin-1 were attenuated in the DOCA-salt group. These results indicated that the increased tissue level of endothelin-1 may decrease the ET-A receptor-mediated vascular response to endothelin-1. However, the ET-B receptor-mediated vasoconstriction is potentiated during DOCA-salt hypertension.     

Extracellular calcium and altered vascular responsiveness in the deoxycorticosterone acetate-salt rat

This study investigated the effects of altered extracellular Ca2+ on in vitro femoral arterial smooth muscle responsiveness in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Compared with controls, femoral arteries from DOCA-salt rats showed a significant increase in sensitivity to KCl and norepinephrine in normal Ca2+ (2.5 mM). Although no difference in maximal contractile response to KCl was observed between groups, there was a significant difference in maximal response to norepinephrine. Dose-response curves in low Ca2+ (0.25 mM) resulted in a significant decrease in the sensitivity of femoral arteries from DOCA-salt rats to KCl and NE so that the responses were similar to those of controls. Relaxation of femoral arteries from DOCA-salt rats after washout of the KCl contraction was significantly slower than that of controls in both low and normal Ca2+. Isoproterenol-induced relaxation of femoral arteries from DOCA-salt rats was significantly attenuated in normal Ca2+. Sensitivity of femoral arteries from DOCA-salt rats to isoproterenol increased in low Ca2+, but maximal relaxation was unaltered. Whereas no difference in maximal relaxation to NaNO2 was seen in femoral arteries from either group in normal Ca2+, a significant decrease in sensitivity to NaNO2 was observed in femoral arteries from DOCA-salt rats. In low Ca2+ the response of femoral arteries from DOCA-salt rats to NaNO2 was similar to that of controls. These results suggest that the increased vascular smooth muscle responsiveness to KCl and norepinephrine seen in DOCA-salt hypertension is due to increased sensitivity of the vascular smooth muscle to Ca2+. Extracellular Ca2+, however, plays only a minor role in the decreased vasodilator responsiveness seen in this form of hypertension.     

Cardiac contractile and coronary flow reserves in deoxycorticosterone acetate-salt hypertensive rats

Cardiac contractility and coronary flow were compared in conscious rats with established deoxycorticosterone acetate-salt hypertension and in those with sham treatment. The hypertensive rats showed a 32% increase in left ventricular/body weight ratio at 9 weeks of treatment and 42% at 18 weeks of treatment. Resting peak rate of change of pressure (dp/dt) was unchanged at 9 weeks and increased at 18 weeks in hypertensive rats, while isoproterenol-stimulated maximal, propranolol-induced minimal, and Ca2+-stimulated maximal peak dp/dt were greater at 18 weeks. These data indicate the preservation of contractile function. At 18 weeks, the beta-adrenergic receptor-mediated contractile reserve, estimated from isoproterenol-stimulated maximal and resting peak dp/dt, was reduced but the propranolol-induced decrease in peak dp/dt was increased in hypertensive rats compared with sham-treated rats. Thus, at this stage, a greater portion of the total contractile capacity appeared to be mobilized with prolongation of hypertension and progression of left ventricular hypertrophy. No differences were observed in left ventricular and right ventricular coronary flow (microspheres) and left ventricular inner/outer flow ratio at rest and with dipyridamole-induced maximal coronary dilatation, at 9 and 18 weeks. There were no alterations in left or right ventricular coronary flow reserves, as estimated from resting and dipyridamole-induced values. The minimal coronary vascular resistance (normalized for gram of tissue) of both the left and right ventricles was increased at either stage, which suggests the occurrence of structural coronary vascular changes. Thus, basal coronary flow and a coronary flow reserve were uncompromised despite evidence of structural coronary vascular alterations in these hypertensive rats.     

Adrenomedullin gene delivery attenuates hypertension, cardiac remodeling, and renal injury in deoxycorticosterone acetate-salt hypertensive rats

Adrenomedullin (AM) is a potent vasodilator and natriuretic peptide that plays an important role in cardiorenal function. In this study, we explored the potential protective role of AM in volume-dependent hypertension by somatic gene delivery. Adenovirus containing the human AM cDNA under the control of the cytomegalovirus promoter/enhancer was administered into deoxycorticosterone acetate (DOCA)-salt hypertensive rats via tail vein injection. A single injection of the human AM gene resulted in a prolonged reduction of blood pressure with a maximal reduction of 41 mm Hg 9 days after gene delivery. Human AM gene delivery enhanced renal function, as indicated by a 3-fold increase in renal blood flow and a 2-fold increase in glomerular filtration rate (n=5, P<0.05). Histological examination of the kidney revealed a significant reduction in glomerular sclerosis, tubular injury, luminol protein cast accumulation, and interstitial fibrosis as well as urinary protein. Human AM gene delivery caused significant decreases in left ventricular weight and cardiomyocyte diameter, which were accompanied by reduced interstitial fibrosis and extracellular matrix formation within the heart. Expression of human AM mRNA was detected in the kidney, adrenal gland, heart, aorta, lung, and liver; immunoreactive human AM levels were measured in urine and plasma. Significant increases in urinary and cardiac cAMP levels were observed in DOCA-salt rats receiving the human AM gene, indicating activation of the AM receptor. These findings showed that AM gene delivery attenuates hypertension, protects against cardiac remodeling and renal damage in volume-overload hypertension, and may have significance in therapeutic applications in cardiovascular and renal diseases.     

Deletion of transient receptor potential vanilloid type 1 receptors exaggerates renal damage in deoxycorticosterone acetate-salt hypertension

To determine whether the transient receptor potential vanilloid type 1 (TRPV1) channel provides protection against hypertension-induced renal damage, hypertension was induced by uninephrectomy and by giving deoxycorticosterone acetate (DOCA)-salt in wild-type (WT) and TRPV1-null mutant (TRPV1-/-) mice. Mean arterial pressure, as determined by radiotelemetry, increased significantly and reached the peak 7 days after DOCA-salt treatment in both WT and TRPV1-/- mice. There was no difference in mean arterial pressure between the 2 strains at the baseline or at the peak that lasted for 4 treatment weeks. DOCA-salt treatment in both WT and TRPV1-/- mice led to increased urinary excretion of albumin and 8-isoprostane, glomerulosclerosis, renal cortical tubulointerstitial injury, tubulointerstitial fibrosis, increased number of tubular proliferating cell nuclear antigen-positive cells, and renal monocyte/macrophage infiltration, all of which were much more severe in DOCA-salt-treated TRPV1-/- compared with DOCA-salt-treated WT mice. Renal TRPV1 protein expression, but not the renal anandamide content, was elevated in DOCA-salt-treated WT compared with vehicle-treated WT mice. Renal anandamide levels were markedly elevated in DOCA-salt-treated TRPV1-/- but not in vehicle-treated TRPV1-/- mice. Thus, our data show that ablation of the TRPV1 gene exacerbates renal damage induced by DOCA-salt hypertension, indicating that TRPV1 may constitute a protective mechanism against end-organ damage induced by hypertension.     

Impaired purinergic neurotransmission to mesenteric arteries in deoxycorticosterone acetate-salt hypertensive rats

Sympathetic nerves release norepinephrine and ATP onto mesenteric arteries. In deoxycorticosterone acetate (DOCA)-salt hypertensive rats, there is increased arterial sympathetic neurotransmission attributable, in part, to impaired prejunctional regulation of norepinephrine release. Prejunctional regulation purinergic transmission in hypertension is less well understood. We hypothesized that alpha(2)-adrenergic receptor dysfunction alters purinergic neurotransmission to arteries in DOCA-salt hypertensive rats. Mesenteric artery preparations were maintained in vitro, and intracellular electrophysiological methods were used to record excitatory junction potentials (EJPs) from smooth muscle cells. EJP amplitude was reduced in smooth muscle cells from DOCA-salt (4+/-1 mV) compared with control arteries (9+/-1 mV; P<0.05). When using short trains of stimulation (0.5 Hz; 5 pulses), the alpha(2)adrenergic receptor antagonist yohimbine (1 micromol/L) potentiated EJPs in control more than in DOCA-salt arteries (180+/-35% versus 86+/-7%; P<0.05). Norepinephrine (0.1 to 3.0 micromol/L), the alpha(2)adrenergic receptor agonist UK 14304 (0.001 to 0.100 micromol/L), the A(1) adenosine receptor agonist cyclopentyladensosine (0.3 to 100.0 micromol/L), and the N-type calcium channel blocker omega-conotoxin GVIA (0.0003 to 0.1000 micromol/L) decreased EJP amplitude equally well in control and DOCA-salt arteries. Trains of stimuli (10 Hz) depleted ATP stores more completely, and the latency to EJP recovery was longer in DOCA-salt compared with control arteries. These data indicate that there is reduced purinergic input to mesenteric arteries of DOCA-salt rats because of decreased ATP bioavailability in sympathetic nerves. These data highlight the potential importance of impaired purinergic regulation of arterial tone as a target for drug treatment of hypertension.     

Vascular but not cardiac remodeling is associated with superoxide production in angiotensin II hypertension

OBJECTIVE: Angiotensin (Ang) II increases reactive oxygen species (ROS), decreases nitric oxide (NO) bioavailability and promotes cardiovascular remodeling. ROS have been identified as critical second messengers of the trophic responses by Ang II. In rats with Ang II-induced hypertension, we investigated the role of ROS in cardiac hypertrophy as well as the remodeling of aortas and mesenteric (resistance) arteries. METHODS: Sprague-Dawley rats received Ang II (0.7 mg/kg per day by mini-pump, n = 7) or vehicle (n = 7) for 5 days. Endothelium-dependent relaxation to acetylcholine (EDR) in aortas was determined in organ baths and in mesenteric resistance vessels in a pressurized myograph. Superoxide (O2) production was measured by lucigenin chemiluminescence, laser-confocal fluorescence microscopy (LCM) and NADPH oxidase assay. RESULTS: Ang II-treated rats developed hypertension (183 +/- 3 versus 138 +/- 4 mmHg, P < 0.05), increased aortic O2 (50%), aortic hypertrophy (12%) and impaired EDR. Mesenteric arteries manifested impaired EDR, increased NADPH oxidase activity (356%) and eutrophic inward remodeling (decreased lumen diameter and increased wall/lumen ratio). However, although Ang II-treated rats developed cardiac hypertrophy (13%), this was not accompanied by an increase in cardiac O2, as measured by lucigenin, LCM or NADPH oxidase assay. On the other hand, cardiac calcineurin, a molecule that promotes cardiac hypertrophy linked to Ang II, was increased by 40% (52 +/- 8 versus 33 +/- 5 pmol/min per mg protein, P < 0.05). CONCLUSION: These studies demonstrate that the role of ROS in Ang II-induced vascular remodeling differ across vascular territories. Although in conduit and resistance vessels, vascular hypertrophy and endothelial dysfunction are linked to increased ROS production, cardiac hypertrophy is not. Instead, cardiac hypertrophy is associated, at least in part, with an increase in calcineurin. These studies unveil novel mechanisms that may play an important role in the pathogenesis of cardiac and vascular injury in hypertension.