Central cardiovascular action of urotensin II in conscious rats

OBJECTIVE: To examine the central cardiovascular action of urotensin II in conscious rats. METHODS: Intracerebroventricular (ICV) injections of urotensin II (1 and 10 nmol) were carried out in conscious Wistar rats. The effects of intravenous (i.v.) urotensin II (10 nmol) were also determined. RESULTS: The ICV injection of urotensin II at a dose of 1 nmol did not alter the arterial pressure or heart rate significantly, while 10 nmol urotensin II increased the arterial pressure and heart rate. The mean arterial pressure at 5 min of ICV urotensin II was 121 +/- 4 mmHg, which was significantly higher than that obtained by ICV injection of artificial cerebrospinal fluid (107 +/- 3 mmHg, P <0.05). In addition, significant increases in heart rate were observed 5-15 min after ICV urotensin II. Pre-treatment with pentolinium (5 mg/kg, i.v.) significantly attenuated the increases in mean arterial pressure (20 +/- 3 versus 8 +/- 2 mmHg, P <0.01) and heart rate (78 +/- 18 versus 7 +/- 5 beats/min, P <0.05) induced by ICV urotensin II. On the other hand, i.v. injection of urotensin II (10 nmol) elicited a depressor response associated with tachycardia; mean arterial pressure 5 min after injection was significantly lower in the urotensin II-injected rats (89 +/- 5 mmHg) than in the control rats (102 +/- 2 mmHg, P <0.05), and the heart rate was significantly higher in the former (402 +/- 11 versus 360 +/- 9 beats/min, respectively, P <0.05). CONCLUSIONS: Central urotensin II produces pressor and tachycardic responses through sympathetic activation, while peripheral urotensin II exerts a vasodilation-mediated depressor response in conscious rats.     

Urotensin II induces phenotypic differentiation, migration, and collagen synthesis of adventitial fibroblasts from rat aorta

BACKGROUND: Urotensin II is a new potent vasoconstrictor. Nevertheless, little is known about its effects on the activation of adventitial fibroblasts. OBJECTIVE: To explore the effects of urotensin II on phenotypic differentiation, migration, and collagen I synthesis of rat aortic adventitial fibroblasts. METHODS: Growth-arrested adventitial fibroblasts were incubated in serum-free medium with urotensin II and some inhibitors of signal transduction pathways. The alpha-smooth muscle-actin expression, collagen I synthesis and migration of adventitial fibroblasts induced by urotensin II were evaluated by western blot, enzyme-linked immunosorbant assay, and the transwell technique, respectively. RESULTS: Urotensin II induced the [alpha]-smooth muscle-actin expression in a dose-dependent and time-dependent manner, with maximal effect at a concentration of 10(-8) mol/l at 24 h (79.9%); it also caused a dose-dependent increase in collagen I synthesis, with maximal effect at a concentration of 10(-7) mol/l (42.6%). The Ca2+ channel blocker nicardipine (10(-5) mol/l), protein kinase C inhibitor H7 (10(-5) mol/l), Rho protein kinase inhibitor Y-27632 (10(-5) mol/l), calcineurin inhibitor cyclosporine A (10(-5) mol/l), and mitogen-activated protein kinase inhibitor PD98059 (10(-5) mol/l) inhibited urotensin II-induced increases in [alpha]-smooth muscle-actin expression and collagen synthesis. Meanwhile, urotensin II stimulated the migration of adventitial fibroblasts dose dependently, with maximal effect at a concentration of 10(-8) mol/l, which was 5.7-fold greater than that of the control. This effect could also be inhibited by PD98059, H7, cyclosporine A, and Y-27632 but not nicardipine. CONCLUSION: Urotensin II may stimulate adventitial fibroblasts phenotypic conversion, migration, and collagen I synthesis through the protein kinase C, mitogen-activated protein kinase, calcineurin, Rho kinase, and/or Ca2+ signal transduction pathways, contributing to the development of vascular remodeling through adventitial fibroblasts activation.     

Central cardiovascular action of urotensin II in spontaneously hypertensive rats.

We have previously reported that urotensin II acts on the central nervous system to increase blood pressure in normotensive rats. In the present study, we have determined the central cardiovascular action of urotensin II in spontaneously hypertensive rats (SHR). Intracerebroventricular (ICV) injection of urotensin II elicited a dose-dependent increase in blood pressure in both SHR and normotensive Wistar-Kyoto rats (WKY). The changes in mean arterial pressure induced by ICV urotensin II at doses of 1 and 10 nmol in the WKY were 8 +/- 2 and 23 +/- 3 mmHg, respectively. ICV administration of urotensin II caused significantly greater increases in blood pressure in SHR (16 +/- 3 mmHg at 1 nmol and 35 +/- 3 mmHg at 10 nmol, respectively) compared with those in WKY. Urotensin II (10 nmol) elicited significant and comparable increases in heart rate in SHR (107 +/- 10 bpm) and WKY (101 +/- 21 bpm). Plasma epinephrine concentrations after ICV administration of 10 nmol urotensin II were 203 +/- 58 pmol/ml in SHR and 227 +/- 47 pmol/ml in WKY, which tended to be higher than those in artificial cerebrospinal fluid-injected rats (73+/- 7 and 87 +/- 28 pmol/ml, respectively, p < 0.1). The immunoreactivity of urotensin II receptor GPR 14 was expressed extensively in the glial cells within the brainstem, hypothalamus, and thalamus. These results suggest that central urotensin II may play a role in the pathogenesis of hypertension in SHR. Since GPR 14 was expressed in the glial cells of the brain, urotensin II may act as a neuromodulator to regulate blood pressure.     

The influence of chronic antihypertensive treatment on the central pressor response in SHR.

We examined the influence of chronic antihypertensive treatment on the central pressor response in SHR. Adult male SHR were divided into 5 groups, i.e., those receiving 1) enalapril (Enal: 25 mg/kg/day in drinking water, n=12); 2) losartan (Los: 40 mg/kg/day, n=11); 3) candesartan (Cand: 4 mg/kg/day, n=12); 4) hydralazine+hydrochlorothiazide (H&H: 50+7.5 mg/kg/day, n=9); 5) vehicle (Control: n=9). At 4 weeks of treatment, hypertonic saline (0.25, 0.5 M) was intracerebroventricularly (i.c.v.) injected into conscious rats. Plasma catecholamines were measured before and after i.c.v. injection. On completion of the experiment, heart weight was measured, and angiotensin-converting enzyme (ACE) activity of the cerebrum was determined. All antihypertensive drugs elicited comparable reductions in systolic blood pressure, while heart rate was significantly higher in the H&H group than in the other groups during treatment. Pressor response to i.c.v. hypertonic saline (0.5 M) was significantly smaller in the Enal (12 +/- 3 mmHg) and Cand (11 +/- 2 mmHg) groups than in the Los (22 +/- 2 mmHg), H&H (16 +/- 2 mmHg), and Control (29 +/- 5 mmHg) groups. Plasma catecholamines did not differ among the groups. Heart weight was lowest in the Enal group, followed by the Los and Cand groups. ACE activity of the cerebrum was significantly decreased in the Enal group. The results suggest that chronic treatment with various antihypertensive drugs differentially alters the central pressor response in SHR, and enalapril and candesartan are effective in attenuating this response.     

Role of the serotonergic nervous system in hemodynamic and vasopressin responses to centrally administrated angiotensin-II in spontaneously hypertensive rats

The purpose of the study is to investigate the role of the serotonergic nervous system in centrally administrated angiotensin II (A-II) mediated hemodynamic as well as vasopressin (AVP) responses. Eight-week-old male SHR and age-matched Wistar Kyoto rats (WKY) were used and the experiment was performed in the conscious state. In protocol 1, after resting observation of 30 minutes 10ng of A-II was given intracerebroventricularly (i.c.v.). This was followed by i.c.v. injection of 1 microgram of 5-HT2 receptor antagonist, xylamidine, 50 minutes later; then 10ng of i.c.v. A-II was repeated after 10 minutes (SHR: n = 7, WKY: n = 10). In protocol 2, plasma vasopressin (AVP) was measured in the following groups. In one group, 1.3ml of blood was sampled from the carotid cannula after resting observation, and the same amount of blood from an age-matched donor rat of the same strain was transfused immediately. Two hours later, 10ng of A-II was given i.c.v., and blood was sampled again after 1 minute (SHR: n = 7, WKY: n = 12). In another group, 1 microgram of xylamidine was given i.c.v. and was followed by 10ng of A-II 10 minutes later; then blood was collected after 1 minute (SHR: n = 8, WKY: n = 13). In protocol 1, resting MAP were 144 +/- 6mmHg in SHR and 99 +/- 2mmHg in WKY. I.c.v. A-II elicited a consistent pressor response in both SHR and WKY, but the response was significantly larger in SHR than that in WKY, +45 +/- 3 and +37 +/- 1mmHg, respectively. Xylamidine had no effect on MAP, and repeated A-II produced significant pressor responses. However, the responses were significantly smaller in both SHR (+36 +/- 3mmHg) and WKY (+25 +/- 1mmHg) as compared with those to initial A-II injection. In protocol 2, resting AVP were similar in SHR (1.5 +/- 0.2pg/ml) and in WKY (1.6 +/- 0.1pg/ml). However, after i.c.v. A-II injection, AVP became higher in SHR (131 +/- 14pg/ml) than in WKY (64 +/- 6pg/ml). AVP after A-II injection with xylamidine pretreatment were similar in SHR (48 +/- 6pg/ml) and in WKY (45 +/- 4pg/ml). Since the responses of both MAP and AVP to i.c.v. A-II were larger in SHR, and the responses were effectively suppressed by S2 receptor antagonists, the central serotonergic nervous system may play an important role in the hemodynamic as well as AVP responses to i.c.v. A-II administration.     

The effects of the intracerebroventricular administration of cimetidine on hemodynamics in conscious rats: relation to the sympathetic nervous system

Histamine H2-receptor antagonists administered into the central nervous system have been shown to increase arterial pressure (AP) in anaesthetized animals (Paakkari et al., 1982). Few studies have been reported on the effects of centrally administered cimetidine (CIM), one of the histamine H2-receptor antagonists, in conscious animals. However, the mechanism of the pressor action of histamine H2-receptor antagonists remains unclear. The present study was designed to investigate the hemodynamic effects of intracerebroventricular (i.c.v.) CIM and the interaction between the sympathetic nervous system and histamine receptor system in conscious rats. Male Wistar rats weighing 200 gr were prepared for the experiment under a conscious and minimally restricted state. Five micrograms of i.c.v. saline (SAL-ICV group, n = 5) did not produce significant changes in mean arterial pressure (MAP) or heart rate (HR) (MAP from 85.6 +/- 3.4 to 86.0 +/- 4.3 mmHg and HR from 395.0 +/- 13.9 to 395.2 +/- 8.2 bpm, respectively). Twenty micrograms of i.c.v. phenoxybenzamine (POB-ICV group, n = 6) decreased MAP from 95.8 +/- 4.1 to 85.2 +/- 3.1 mmHg, -10.7 +/- 2.2 mmHg as delta MAP, and increased HR from 392.5 +/- 8.5 to 435.3 +/- 13.9 bpm, +42.8 +/- 6.8 bpm as delta HR. Two-hundred micrograms of intravenous (i.v.) POB (POB-IV group, n = 5) also decreased MAP from 96.0 +/- 4.3 to 71.0 +/- 5.1 mmHg, -25.0 +/- 2.7 mmHg as delta MAP, and increased HR from 395.8 +/- 10.5 to 473.0 +/- 12.4 bpm, +77.2 +/- 7.6 bpm as delta HR. The changes in MAP and HR were much greater in the POB-IV group than those in the other two groups. The subsequent i.c.v. administration of 250 micrograms of CIM induced an increase in MAP (+19.4 +/- 1.7 mmHg as delta MAP) and a decrease in HR (-36.4 +/- 3.1 bpm as delta HR) in the SAL-ICV group, which continued for at least 30 minutes producing peak effects 2 minutes after i.c.v. administration of CIM. However, an elevation of MAP caused by i.c.v. CIM was much more inhibited in the POB-ICV group than in the POB-IV group (+2.5 +/- 0.7 mmHg as delta MAP in the POB-ICV group and +5.0 +/- 1.3 mmHg as delta MAP in the POB-IV group, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)     

Pressor response induced by central angiotensin II is mediated by activation of Rho/Rho-kinase pathway via AT1 receptors

OBJECTIVES: The brain renin-angiotensin system plays an important role in cardiovascular regulation and the pathogenesis of hypertension. Angiotensin II activates the Rho/Rho-kinase pathway in vascular smooth muscle cells and cardiomyocytes in vitro. The aim of the present study was to determine whether angiotensin II in the brainstem activates the Rho/Rho-kinase pathway, and, if so, whether this mechanism is involved in the central pressor action of angiotensin II. METHODS AND RESULTS: Angiotensin II infused intracisternally for 7 days in Wistar-Kyoto rats (WKY) increased systolic blood pressure (SBP) and urinary norepinephrine excretion. These responses were abolished by the co-infusion of Y-27632, a specific Rho-kinase inhibitor, or valsartan. The intracisternal infusion of Y-27632 or valsartan also reduced SBP and norepinephrine excretion in spontaneously hypertensive rats (SHR). Western blot analysis was performed to examine the expression levels of membranous RhoA and phosphorylated ezrin, radixin, and moesin (p-ERM), which reflects Rho/Rho-kinase activity. The expression levels of membranous RhoA and p-ERM in the brainstem were significantly greater in both angiotensin II-treated WKY and SHR than in vehicle-treated WKY. Valsartan reduced the expression levels of membranous RhoA and p-ERM in angiotensin II-treated WKY and SHR. Y-27632 reduced the expression levels of p-ERM in angiotensin II-treated WKY and SHR. CONCLUSIONS: These results suggest that the pressor response induced by intracisternally infused angiotensin II is substantially mediated by the activation of the Rho/Rho-kinase pathway via AT1 receptors of the brainstem in WKY, and that this pathway might be involved in the hypertensive mechanisms of SHR.     

Urotensin II acts centrally to increase epinephrine and ACTH release and cause potent inotropic and chronotropic actions

Urotensin II is a small peptide whose receptor was recently identified in mammals as the orphan G protein-coupled receptor-14. The reported cardiovascular responses to systemic urotensin II administration are variable, and there is little detailed information on its central cardiovascular actions. We examined the cardiovascular and humoral actions of intracerebroventricular urotensin II (0.02 and 0.2 nmol/kg and vehicle) and intravenous urotensin II (2, 20, and 40 nmol/kg and vehicle) in conscious ewes previously surgically implanted with flow probes and intracerebroventricular guide tubes. Two hours after intracerebroventricular infusion of urotensin II (0.2 nmol/kg over 1 hour; n=5), heart rate (+56+/-13 beats per minute [bpm]), dF/dt (an index of cardiac contractility; +533+/-128 L x min(-1) x s(-1)), and cardiac output (+3.4+/-0.4 L/min) increased significantly compared with vehicle, as did renal, mesenteric, and iliac blood flows and conductances. Plasma epinephrine, adrenocorticotropic hormone, and glucose levels also increased dramatically (+753+/-166 pg/mL, +14.3+/-3.5 pmol/L, and +7.0+/-1.4 mmol/L, respectively). All of these variables remained elevated for up to 4 hours after infusion. In contrast, 1 hour after intravenous urotensin II (40 nmol/kg bolus; n=6), a sustained tachycardia (+25+/-8 bpm) ensued, but cardiac output, cardiac contractility, total peripheral conductance, and plasma glucose levels did not change significantly. In summary, this is the first study to show that urotensin II acts centrally to stimulate sympathoadrenal and pituitary-adrenal pathways, resulting in increased adrenocorticotropic hormone and epinephrine release and potent chronotropic and inotropic actions. In contrast, tachycardia was the only major response to intravenous urotensin II. These findings suggest that urotensin II is a novel stimulator of central pathways that mediate responses to alerting stimuli or stress.     

Central modulation of the baroreflex response to phenylephrine in rats. Lack of interaction between calcium channel modulators and the renin-angiotensin system

We have previously shown that a calcium channel activator (BAY K 8644) can decrease the baroreflex control of heart rate in SHR when intracerebroventricularly (i.c.v.) administered. In pentobarbital anesthetized SHR, the inhibitory effect of BAY (3 micrograms/kg i.c.v.) on baroreflex sensitivity (BRS; ramp method: phenylephrine 2 micrograms i.v.; BAY: 0.14 +/- 0.05 vs control: 0.39 +/- 0.08 msec/mmHg; p less than 0.01) was fully suppressed after pretreatment with the muscarinic antagonist atropine methylnitrate (80 micrograms/kg i.c.v.) suggesting the involvement of cholinergic pathways in the inhibitory effect. Since A II was reported to centrally increase arterial pressure through an enhanced release of acetylcholine and to depress BRS, we tested whether the effect of BAY on BRS could involve central A II systems. The A II antagonist [Sar 1Ile8] A II (30 micrograms/kg/min i.c.v.) suppressed the inhibitory effect of A II on BRS (control: 0.32 +/- 0.09; A II: 0.10 +/- 0.02; Sar1 Ile8 + A II: 0.39 +/- 0.08 msec/mmHg) but not the inhibitory effect of BAY (3 mu g/kg i.c.v.) on BRS. These results suggest that the central inhibition of BRS by BAY unlikely involves central A II systems.     

Investigation of signaling pathways that mediate the inotropic effect of urotensin-II in human heart

OBJECTIVE: This study investigated signaling pathways that may contribute to the potent positive inotropic effect of human urotensin-II (hU-II) in human isolated right atrial trabeculae obtained from patients with coronary artery disease. METHODS: Trabeculae were set up in tissue baths and stimulated to contract at 1 Hz. Tissues were incubated with 20 nM hU-II with or without phorbol 12-myristate 13-acetate (PMA, 10 microM) to desensitize PKC, the PKC inhibitor chelerythrine (10 microM), 10 microM 4alpha-phorbol that does not desensitize PKC, the myosin light chain kinase inhibitor wortmannin (50 nM, 10 microM), or the Rho kinase inhibitor Y-27632 (0.1-10 microM). Activated RhoA was determined by affinity immunoprecipitation, and phosphorylation of signaling proteins was determined by SDS-PAGE. RESULTS: hU-II caused a potent positive inotropic response in atrial trabeculae, and this was concomitant with increased phosphorylation of regulatory myosin light chain (MLC-2, 1.8+/-0.4-fold, P<0.05, n=6) and PKCalpha/betaII (1.4+/-0.2-fold compared to non-stimulated controls, P<0.05, n=7). Pretreatment of tissues with PMA caused a marked reduction in the inotropic effect of hU-II, but did not affect hU-II-mediated phosphorylation of MLC-2. The inotropic response was inhibited by chelerythrine, but not 4alpha-phorbol or wortmannin. Although Y-27632 also reduced the positive inotropic response to hU-II, this was associated with a marked reduction in basal force of contraction. RhoA.GTP was immunoprecipitated in tissues pretreated with or without hU-II, with findings showing no detectable activation of RhoA in the agonist stimulated tissues. CONCLUSIONS: The findings indicated that hU-II increased force of contraction in human heart via a PKC-dependent mechanism and increased phosphorylation of MLC-2, although this was independent of PKC. The positive inotropic effect was independent of myosin light chain kinase and RhoA-Rho kinase signaling pathways.     

The role of the RhoA/Rho-kinase signaling pathway in renal vascular reactivity in endothelial nitric oxide synthase null mice

BACKGROUND: Smooth muscle contraction is regulated by the small GTPase RhoA and its target, Rho-kinase and recent evidence indicates that nitric oxide (NO) causes vasodilation through inhibition of the RhoA/Rho-kinase (ROCK) signaling pathway. AIM: This study tested the hypothesis that the enhanced renal vascular tone and systemic hypertension in endothelial nitric oxide synthase (eNOS) null mice is due to disinhibition of the ROCK signaling pathway. METHODS: Systolic blood pressure (SBP) was measured by tail-cuff plethysmography and the isolated Krebs-perfused kidney preparation was used to evaluate renal vascular responses in C57BL/6 (wild type, WT) and eNOS knockout (KO) mice treated with Y-27632, a ROCK inhibitor. RESULTS: Compared with the WT mice, Rho kinase activity was higher in eNOS KO mice (37 +/- 8%, P < 0.05) as was SBP (33 +/- 4%, P < 0.05), basal renal perfusion pressure (31 +/- 4%, P < 0.05) and renal vascular resistance (35 +/- 4%, P < 0.05). Y-27632 abolished these differences. Vasoconstriction elicited by angiotensin II (Ang II) or phenylephrine (PE), G-protein-coupled receptor (GPCR) agonists, but not that elicited by arachidonic acid or KCl, was greater in eNOS KO mice. Y-27632 eliminated the amplified vasoconstriction elicited by Ang II or phenylephrine but to a greater extent in eNOS KO mice. Similarly, responses elicited by guanosine 5'-gamma-thiotriphosphate (GTPgammaS), a non-hydrolyzable GTP analog, or sodium tetrafluoride (NaF4), an activator of G-proteins, was greater in eNOS KO mice, 53 +/- 14 and 50 +/- 3%, respectively. Y-27632 normalized the difference. Y-27632 also elicited a dose-dependent renal vasodilation that was greater in eNOS KO mice. CONCLUSIONS: These results show that the ROCK signaling pathway is amplified in the eNOS KO mouse kidney and that the enhanced renal vascular tone and selective increase in reactivity to GPCR agonists supports a role for ROCK in the hypertension and vascular dysfunction in the eNOS KO mice.     

Key role of myosin light chain (MLC) kinase-mediated MLC2a phosphorylation in the alpha 1-adrenergic positive inotropic effect in human atrium

OBJECTIVE: Mechanisms of the positive inotropic response to alpha(1)-adrenergic stimulation in the heart remain poorly understood, but recent evidence in rat papillary muscle suggests an important role of regulatory myosin light chain (MLC2) phosphorylation. This study investigated alpha(1)-adrenergic contractile effects and the role of MLC kinase (MLCK)-dependent phosphorylation of MLC2 in human atrial muscle strips. METHODS: Force measurement was performed on electrically stimulated atrial muscle strips (n=140; 20 hearts) in the presence of the beta-blocker nadolol. MLC2a phosphorylation was determined by 2D-polyacrylamide gel electrophoresis and Western blotting of muscle strips that were immediately freeze-clamped following force measurements. RESULTS: The alpha(1)-agonist phenylephrine (PE; 0.3-100 microM) exerted a concentration-dependent, monophasic, sustained positive inotropic effect (86% above basal) that was accompanied by an 80% increase in MLC2a phosphorylation. Desinhibition of MLC phosphatase by the Rho kinase inhibitor Y-27632 (10 microM) reduced the effect of PE by 16%. The MLCK inhibitor wortmannin (10 microM) completely abolished both the PE-induced increase in force and MLC2a phosphorylation. The structurally unrelated MLCK inhibitor ML-7 (10 microM) had similar effects. Neither Y-27632 nor wortmannin or ML-7 affected beta-adrenergic force stimulation. In contrast to our findings in atrial muscle strips, we observed no increase in MLC2v phosphorylation after PE in human ventricular muscle strips and wortmannin failed to inhibit PE-induced force of contraction. CONCLUSION: alpha(1)-Adrenergic receptors mediate a prominent increase in contractile force in human atria that depends on MLCK activity and is accompanied by an increase in MLC2 phosphorylation.     

Effects of intracerebroventricular atrial natriuretic factor on angiotensin II- or sodium-induced blood pressure elevation and natriuresis

We examined the effects of intracerebroventricular (i.c.v.) administration of atrial natriuretic factor (ANF) on pressor and natriuretic responses induced by i.c.v. angiotensin II (Ang II) or hypertonic NaCl. Conscious male Wistar rats were given one of the following solutions into the lateral ventricle: artificial cerebrospinal fluid (CSF); rat ANF (99-126) 1.0 microgram/kg per min; Ang II 100 ng/kg per min; 0.6 mol/l NaCl; Ang II plus ANF, and 0.6 mol/l NaCl plus ANF. The i.c.v. infusion of artificial CSF or ANF alone did not cause significant changes in mean blood pressure, urinary volume or sodium excretion (UNaV). The i.c.v. infusion of Ang II or 0.6 mol/l NaCl raised mean blood pressure, decreased urinary volume and increased UNaV. When ANF was administered with Ang II, the Ang II-induced responses were diminished significantly (delta mean blood pressure, +10 +/- 3 versus +20 +/- 4 mmHg; delta urinary volume, -38 +/- 9 versus -78 +/- 5 microliters/min; delta UNaV, +0.49 +/- 0.51 versus +2.28 +/- 0.58 mumol/min). The centrally administered ANF opposed the effects of 0.6 mol/l NaCl, though the effect was significant only in respect of blood pressure. Our results indicate that the brain ANF may have an antinatriuretic role in some conditions.     

Vessel- and vasoconstrictor-dependent role of rho/rho-kinase in renal microvascular tone

We examined the role of Rho/Rho-kinase in renal afferent and efferent arteriolar tone induced by angiotensin (Ang) II, KCl and elevated renal arterial pressure (from 80 to 180 mm Hg), using isolated perfused rat hydronephrotic kidney. In the condition with no vasoconstrictor stimuli, Y-27632, a Rho-kinase inhibitor, dilated only afferent (from 11.6 +/- 0.4 to 14.1 +/- 0.5 microm) but not efferent arterioles (from 11.6 +/- 0.2 to 12.6 +/- 0.7 microm) at 10(-5) mol/l. During renal vasoconstriction by Ang II, Y-27632 restored the afferent arteriolar constriction (141 +/- 10% reversal at 10(-5) mol/l), whereas the ability of Y-27632 to inhibit the Ang II-induced efferent arteriolar constriction was diminished (73 +/- 7% reversal). A similar action was observed with fasudil, another Rho-kinase inhibitor. Furthermore, Y-27632 impaired myogenic afferent arteriolar constriction, with 117 +/- 17% inhibition at 10(-5) mol/l. The inhibition by Y-27632 of the myogenic vasoconstriction was almost the same as that of the Ang II-induced tone of this vessel type. However, Y-27632 had a modest effect on KCl-induced vasoconstriction of afferent arterioles. In conclusion, the present study demonstrates a predominant role of Rho/Rho-kinase in mediating the basal and Ang II-induced tone of afferent, but not efferent, arterioles. Furthermore, the role of Rho/Rho-kinase in afferent arteriolar constriction differs, with a substantial contribution to Ang II-induced and myogenic constriction but a minimal role in depolarization-induced constriction. Since Ang II-induced, KCl-induced and myogenic constriction of afferent arterioles require calcium entry through voltage-dependent calcium channels, the interaction between Rho/Rho-kinase and the calcium entry pathway may determine the afferent arteriolar tone induced by these stimuli.     

Effects of intracerebroventricular (I.C.V.) administration of 5-hydroxytryptamine (5-HT) on hemodynamics in conscious spontaneously hypertensive rats (SHR): relation to sympathetic nervous system

Recently, the serotonergic nervous system has been receiving attention as part of the blood pressure regulating mechanism of the central nervous system, and it has been postulated that the system may participate in the pathogenesis of hypertension. The purpose of this experiment is to investigate the mechanism of hemodynamic change after i.c.v. administration of 5-HT in SHR and in normotensive Wistar Rats (WR). MATERIALS AND METHODS: Twenty-week-old male SHR (n = 11) and age-matched WR (n = 14) were used. On the day before the experiments, the unilateral carotid artery and jugular vein were cannulated. Also, a cannula was inserted stereotaxically into the anterior horn of the lateral cerebral ventricle. Experiments were performed under the conscious and minimum restrained state. Experiment I: After observation of resting mean arterial pressure (MAP) and heart rate (HR) for 20 minutes, 5-HT (5 micrograms/5 microliter saline) was administrated i.c.v., and MAP and HR were observed for 90 minutes. Then, 200 micrograms of phenoxybenzamine (POB) was given from the jugular cannula. Thirty minutes after the POB administration when MAP was stabilized, 5 micrograms of 5-HT was again given i.c.v., and MAP and HR were recorded for 30 minutes. Experiment II: Plasma norepinephrine (PNE) was measured before and 2 minutes after 5-HT i.c.v. administration. The control sample (1.5 ml) was withdrawn at least 30 minutes before the 5-HT injection, and immediately after the blood sampling, the same amount of blood which was obtained from the age-matched donor rat of the same strain was transfused. RESULTS: Experiment I: Resting MAP was 136.4 +/- 5.1 mmHg in SHR and 99.1 +/- 3.0 mmHg in WR. I.c.v. administration of 5-HT elicited consistent pressor response in SHR and in WR.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduction of the pressor effect of fluoxetine after V1A-vasopressin receptor blockade in the conscious rats]

Pharmacovigilance data have reported some cases of arterial hypertension in patients treated with serotonin reuptake inhibitors. This side effect is now called serotonin syndrome. Moreover, some authors have shown that these drugs could reduce, at least in part, the fall in blood pressure (BP) observed in experimental models or in human forms of orthostatic hypotension, suggesting a modulation of the autonomic nervous system by these drugs. These data led us to study in freely moving Wistar rats the mechanisms involved and the putative involvement of autonomic nervous system. Intracerebroventricular (i.c.v.) administration of fluoxetine (5-50 micrograms) induced an increase in BP similar to which was obtained following central administration of serotonin (5-HT) (0.5-5 micrograms). After 5-HT, the pressor effect was immediate (1 min following injection) and involved the baroreflex pathway (bradycardia). The fluoxetine-induced pressor response reached its maximal 1 hour after injection without any significant change in heart rate (HR). At the dose of 10 micrograms i.c.v., fluoxetine significantly increased mean BP by 16 +/- 4 mmHg. This pressor response was partially but significantly reduced by a pretreatment by the alpha 1-adrenoreceptor antagonist, prazosin (500 micrograms.kg-1 i.v.) (+7 +/- 4 mmHg, p < 0.05) or by a V1A-vasopressin receptor antagonist (20 micrograms.kg-1 i.v.) (+5 +/- 3 mmHg, p < 0.05). However, pretreatment by the beta-adrenoreceptor antagonist, propranolol (1 mg.kg-1 i.v.) and the antagonist 5-HT2, ketanserine (5 mg.kg-1 i.v.) did not modify the fluoxetine-induced pressor response. In freely moving rats receiving fluoxetine (10 micrograms i.c.v.), vasopressin plasma levels were significantly higher (+39 +/- 5 pg.mL-1) than in rats receiving saline (100 microL i.c.v.) (+14 +/- 4 pg.mL-1), thus confirming the involvement of vasopressinergic mechanisms in the fluoxetine-induced pressor response. These data suggest that in freely moving Wistar rats, central acute administration of fluoxetine induces a pressor response mediated by both an increase in sympathetic tone and a vasopressin release. This observation could suggest the putative use of alpha 1-adrenoreceptors antagonists and/or V1A-vasopressin receptor antagonists in the treatment of the serotonin syndrome.     

Cardiovascular responses to glutamate and angiotensin II in ventrolateral medulla of hypertension induced by chronic inhibition of nitric oxide.

It has been suggested that nitric oxide (NO) influences the actions of L-glutamate and angiotensin II in the brain. In the present study, we examined whether cardiovascular responses to L-glutamate and angiotensin II would be altered in the rostral ventrolateral medulla (RVLM) of rats treated with an NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). Wistar rats were treated with either L-NAME (100 mg/kg/day, n=9) or vehicle (n=8) for 4 weeks. L-glutamate (2 nmol/50 nl) or angiotensin 11 (100 pmol) was then microinjected into unilateral RVLM of anesthetized rats. Upon completion of the experiments, angiotensin-converting enzyme (ACE) activity of the brain stem was measured. The systolic blood pressure after 4 weeks of the treatment was significantly higher in the L-NAME group (203+/-8 mmHg) than in the control group (142+/-3 mmHg, p< 0.01). The pressor response to L-glutamate microinjected into the RVLM was significantly greater in the L-NAME group (31+/-2 mmHg) than in the control group (24+/-1 mmHg, p< 0.01). Similarly, angiotensin II showed a greater pressor response in the L-NAME group. ACE activity of the brain stem did not differ between the groups. In conclusion, NO may have an inhibitory influence on the actions of L-glutamate and angiotensin II in the RVLM.     

Chronic administration of a tyrosine kinase inhibitor restores functional and morphological changes of the basilar artery during chronic hypertension

OBJECTIVE: Activation of tyrosine kinase appears to play an important role in pathogenesis of cardiovascular disease during chronic hypertension. In the present study, we tested the hypothesis that long-term treatment with an inhibitor of tyrosine kinase would have beneficial effects on hypertension-induced morphological and functional changes of the cerebral artery. METHODS: Male spontaneously hypertensive rats (SHR; 4 months old) were fed normal rat chow, or that containing an inhibitor of tyrosine kinase, genistein (1 mg/kg chow). Normotensive Wistar-Kyoto (WKY) rats were also fed either of the chows. After feeding the rats for 2 months, we measured wall thickness, diameter of the basilar artery and its dilator responses to acetylcholine (ACh); Y-26763, an opener of ATP-sensitive potassium channels; and Y-27632, an inhibitor of Rho-associated kinase. RESULTS: Treatment with genistein did not cause significant changes in physiological variables, including mean arterial pressure in either strain. In control SHR, the wall thickness of the basilar artery was greater than that of WKY rats. Genistein treatment reduced the wall thickness significantly in SHR. Vasodilator responses induced by ACh and Y-26763 were markedly attenuated in SHR compared to WKY rats, and treatment of SHR with genistein significantly improved the vasodilatation. Dilatation of the artery in response to Y-27632 was enhanced in SHR compared to WKY rats and treatment of SHR with genistein did not affect the enhanced vasodilator responses to Y-27632. CONCLUSIONS: Chronic treatment with genistein may be a novel approach to prevent cerebrovascular disorders.     

Rho/Rho kinase is a key enzyme system involved in the angiotensin II signaling pathway of liver fibrosis and steatosis

BACKGROUND AND AIM: The molecular mechanisms underlying the involvement of the renin-angiotensin system in hepatic fibrosis are unclear. Recently, it was reported that a Rho kinase inhibitor prevented fibrosis of various tissues and that the Rho/Rho kinase pathway was involved in the renin-angiotensin system of vascular smooth muscle cells. In this study, the involvement of the Rho/Rho kinase pathway on angiotensin II signaling in liver fibrogenesis and generation of steatosis was investigated. METHODS: Rats were fed a choline-deficient/L-amino acid-defined (CDAA) diet continuously and treated with a Rho kinase inhibitor, Y-27632, and an angiotensin II receptor blocker, TCV-116. Liver histology and hepatic stellate cell activation were analyzed. Free radical production was detected by 4-hydroxynonenal and 8-hydroxy-2'-deoxyguanosine immunostaining and the expression of tumor necrosis factor-alpha was examined. Isolated hepatic stellate cells were pretreated with a Rho kinase inhibitor, Y-27632, or an angiotensin II receptor blocker, CV-11974, and stimulated with angiotensin II, and mRNA expression of transforming growth factor-beta and alpha-smooth muscle actin was analyzed. RESULTS: Both the angiotensin II receptor blocker and the Rho kinase inhibitor improved fibrosis and steatosis of the liver in CDAA-fed rats. The increase in the number of hepatocytes positive for 4-hydroxynonenal and 8-hydroxy-2'-deoxyguanosine in CDAA-fed rats was significantly prevented by the angiotensin II receptor blocker and the Rho kinase inhibitor. The levels of tumor necrosis factor-alpha mRNA in the liver of CDAA-fed rats were significantly increased and this increase was significantly inhibited by treatment with the angiotensin II receptor blocker and the Rho kinase inhibitor. mRNA expression of transforming growth factor-beta and alpha-smooth muscle actin stimulated by angiotensin II was also significantly suppressed by these two drugs. CONCLUSION: These results suggest that the Rho/Rho kinase pathway is at least partly involved in the renin-angiotensin system and plays an important role in hepatic fibrosis and steatosis.