The effect of nitric oxide inhibition on blood pressure depends on rat strain

Protection by selective mTORC2 inhibition of Zymosan-induced hypotension and systemic inflammation mediated via IKKα/IκB-α/NF-κB activation

Non-septic shock is a serious condition leading to multiple organ dysfunction. Although targeting the mammalian target of the rapamycin complex 1 (mTORC1) signaling pathway exerts potent anti-inflammatory activity, little is known about mTORC2's contribution to non-septic shock. Thus, our research aims to investigate mTORC2's contribution and associated changes of IκB kinase (IKKα)/inhibitor κB (IκB-α)/nuclear factor-ĸB (NF-κB) pathway on Zymosan (ZYM)-induced non-septic rat model using the novel mTORC2 selective inhibitor JR-AB2-011. Rats were given saline (4 ml/kg), dimethylsulfoxide (DMSO) (4 ml/kg), ZYM (500 mg/kg), and (or) JR-AB2-011 (1 mg/kg). Mean arterial pressure (MAP) and heart rate (HR) of rats were recorded. JR-AB2-011 reversed both ZYM-induced reduction in MAP and increase in HR. Protein expression and/or phosphorylation of rictor, protein kinase B (Akt), IκB-α, IKKα, NF-κB p65, inducible nitric oxide synthase (iNOS), nitrotyrosine, cyclooxygenase 2 (COX-2), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, besides prostaglandin (PG) E2 levels were measured. The enhanced expression of the proteins mentioned above has been inhibited by JR-AB2-011. These data suggest mTORC2's promising role in ZYM-induced hypotension and systemic inflammation mediated via IKKα/IκB-α/NF-κB pathway.

Effects of nitric oxide synthase inhibition with or without cyclooxygenase-2 inhibition on resting haemodynamics and responses to exendin-4

BACKGROUND AND PURPOSE

Interactions between the NO system and the cyclooxygenase systems may be important in cardiovascular regulation. Here we measured the effects of acute cyclooxygenase-2 inhibition (with parecoxib), alone and in combination with NOS inhibition (with NG-nitro-L-arginine methyl ester (L-NAME)), on resting cardiovascular variables and on responses to the glucagon-like peptide 1 agonist, exendin-4, which causes regionally-selective vasoconstriction and vasodilatation.

EXPERIMENTAL APPROACH

Rats were instrumented with flow probes and intravascular catheters to measure regional haemodynamics in the conscious, freely moving state. L-NAME was administered as a primed infusion 180 min after administration of parecoxib or vehicle, and exendin-4 was given 60 min after the onset of L-NAME infusion.

KEY RESULTS

Parecoxib had no effect on resting cardiovascular variables or on responses to L-NAME. Exendin-4 caused a pressor response accompanied by tachycardia, mesenteric vasoconstriction and hindquarters vasodilatation. Parecoxib did not affect haemodynamic responses to exendin-4, but L-NAME inhibited its hindquarters vasodilator and tachycardic effects. When combined, L-NAME and parecoxib almost abolished the hindquarters vasodilatation while enhancing the pressor response.

CONCLUSIONS AND IMPLICATIONS

Cyclooxygenase-2-derived products do not affect basal haemodynamic status in conscious normotensive rats, or influence the NO system acutely. The inhibitory effects of L-NAME on the hindquarters vasodilator and tachycardic effects of exendin-4 are consistent with a previous study that showed those events to be beta-adrenoceptor mediated. The additional effect of parecoxib on responses to exendin-4 in the presence of L-NAME, is consistent with other evidence for enhanced involvement of vasodilator prostanoids when NO production is reduced.

L-NAME-induced neutrophil accumulation in rat lung is not entirely because of interactions with L- and P-selectins or CD18

BACKGROUND/PURPOSE

Nitric oxide (NO) is a known selective dilator of the pulmonary vascular tree. There is evidence that it also plays a role in diminishing neutrophil adherence to vascular endothelial cells. Close examination of these effects of NO on the pulmonary microcirculation is essential to our understanding of its mechanisms of action as well as its potential as a therapeutic agent to reduce neutrophil sequestration, and its subsequent damage, in a variety of conditions that cause lung injury and inflammation. This study explores the mechanism by which endogenous NO influences neutrophil-endothelial cell interactions by examining the effects of the adhesion molecule blockers, fucoidin, and anti-CD18 antibody.

METHODS

Lung samples from 10 sets of rats (n = 4 for each study group) were studied. Each rat received an intravenous bolus of normal saline, fucoidin, or anti-CD18 antibody, followed by a 1-hour infusion of normal saline or N omega-nitro-L-arginine methyl ester (L-NAME) at 2 mg kg(-1) min(-1). The accumulation of neutrophils within the lungs was assessed quantitatively by myeloperoxidase assay.

RESULTS

Fucoidin application decreased some neutrophil activity, but this may have been independent of the effects on L-NAME activity. The anti-CD18 pretreatment did not have a significant effect on any of the groups in the presence or absence of L-NAME.

CONCLUSIONS

These data indicate that L-NAME does not conclusively produce its associated increase in neutrophil activity in the baseline state of the lungs via an interaction with L-selectin, P-selectin, or CD18. Rather, the inhibition of NO may lead to the expression of a different adhesion molecule or factor that is normally not expressed in the presence of NO. Endogenous NO may also possibly influence neutrophil-endothelial interaction by affecting hemodynamics rather than actions of adhesion molecules.

Nitric oxide synthase-inhibition hypertension is associated with altered endothelial cyclooxygenase function

We reported previously that endothelium-intact superior mesenteric arteries (SMA) from Nω-nitro-l-arginine (l-NNA)-treated hypertensive rats (LHR) contract more to norepinephrine (NE) than SMA from control rats. Others have shown that nitric oxide (NO) synthase (NOS) inhibition increases cyclooxygenase (COX) function and expression. We hypothesized that augmented vascular sensitivity to NE in LHR arteries is caused by decreased NOS-induced dilation and increased COX product-induced constriction. We observed that the EC50 for NE is lower in LHR SMA compared with control SMA (control −6.37 ± 0.04, LHR −7.89 ± 0.09 log mol/l; P < 0.05). Endothelium removal lowered the EC50 (control −7.95 ± 0.11, LHR −8.44 ± 0.13 log mol/l; P < 0.05) and increased maximum tension in control (control 1,036 ± 38 vs. 893 ± 21 mg; P < 0.05) but not LHR (928 ± 30 vs. 1,066 ± 31 mg) SMA. Thus augmented NE sensitivity in LHR SMA depends largely on decreased endothelial dilation. NOS inhibition (l-NNA, 10−4 mol/l) increased maximum tension and EC50 in control arteries but not in LHR arteries. In contrast, COX inhibition decreased maximum tension in control arteries, suggesting that COX products augment contraction. Indomethacin did not affect NE-induced contraction in l-NNA-treated or denuded arteries. In control SMA loaded with the fluorescent NO indicator 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate, indomethacin increased and l-NNA decreased NO release. Therefore, COX products appear to inhibit NO production to augment NE-induced contraction. With chronic NOS inhibition, this modulating influence is greatly diminished. Thus, in NOS-inhibition hypertension, decreased activity of both COX and NOS pathways profoundly disrupts endothelial modulation of contraction.

Effects of long-term captopril andl-arginine treatment on ventilation and blood pressure in obese male SHHF rats

We investigated the effects of captopril (Cap) and l-arginine (Arg) on hypertension and cardiopulmonary function. Our hypothesis was that Cap therapy or Arg will improve cardiopulmonary risk factors for hypertension and hypoventilation in the obese spontaneously hypertensive heart failure rat, which is characterized by hypertension, obesity, and disorders of lipid and carbohydrate metabolism. For the first study, one group of rats received Cap in drinking water, and a second group received deionized water (DI). For the second study, rats were further subdivided. Some Cap-treated rats continued on this treatment, and the other half were now given DI to determine whether there would be residual effects of Cap treatment. A subgroup of rats who had received DI was then given Arg, whereas the rest remained on DI. In the first study, Cap-treated rats exhibited decreases in systolic and diastolic blood pressures, frequency of breathing, and minute ventilation, but ventilatory control was maintained. In contrast, blood pressures and relative ventilation to metabolism were higher in the DI-treated group. Removal of Cap increased blood pressure and decreased tidal volume while these rats maintained frequency. Although Arg-treated rats did not exhibit a decrease of blood pressure, ventilation was maintained in this group by preserving tidal volume. Thus Cap and Arg affected ventilation through different mechanisms independent of blood pressure.

Effect of nitric oxide on prolactin secretion and hypothalamic biogenic amine contents

Involvement of nitric oxide (NO) in the episodic secretion of prolactin was studied in conscious freely moving adult rats. Prolactin secretion was pulsatile in all animals of either group during the bleeding period (from 10:30 h to 13:30 h). Administration of N(omega)-nitro-L-arginine methyl ester (L-NAME), a NO synthase inhibitor, increased mean plasma levels of prolactin, and the absolute amplitude of prolactin peaks during the whole bleeding period as compared to values found in the control group. L-NAME increased norepinephrine (170%), dopamine (58.27%) and serotonin contents (30%) in the anterior hypothalamus. In the median eminence, dopamine and serotonin contents decreased (19.79% and 33.9% respectively) after L-NAME as compared to the values found in controls. In addition, norepinephrine content increased in mediobasal hypothalamus (79.6%) of rats treated with L-NAME. The results indicate that changes in NO production may modify the episodic secretion of prolactin. These effects were associated with changes in hypothalamic and median eminence biogenic amines.

Blocking of endogenous nitric oxide increases white blood cell accumulation in rat lung

BACKGROUND/PURPOSE

Nitric oxide (NO) is a known selective dilator of the pulmonary vascular tree. There also is evidence that it plays a role in diminishing neutrophil adherence to vascular endothelial cells. An understanding of these effects of NO on the pulmonary microcirculation is essential to our understanding of its mechanisms of action as well as its potential as a therapeutic agent to reduce neutrophil sequestration and subsequent lung injury and inflammation from a variety of conditions. This study examines the direct effects of inhibition of endogenous NO synthesis with the L-arginine analog, Nomega-nitro-L-arginine methyl ester (L-NAME) on neutrophil accumulation within the lung.

METHODS

Lung samples from 2 groups of rats (n = 14 for each study group) were studied. One group was given an intravenous infusion of L-NAME, and the other received normal saline (NS), at 2 mg/kg/min for 1 hour. The accumulation of neutrophils within the lungs was assessed quantitatively by myeloperoxidase (MPO) assay as well as by microscopic examination by a pathologist blinded to the 2 groups.

RESULTS

The L-NAME group showed increased MPO activity in the lung compared with the NS group (mean MPO/mean bicinchoninic acid [BCA]: 43.46 +/- 3.10 U/microg v 23.58 +/- 2.48 U/microg; mean MPO/g wet lung [gwl]: 57.60 +/- 5.98 U/gwl v 27.10 +/- 3.84 U/gwl, mean +/- SEM; P <.05). Histologic examination (n = 6 each group) showed 26 +/- 2 neutrophils/5 hpf for the L-NAME group versus 18 +/- 1 neutrophils/5 hpf for the NS group (P < 0.05).

CONCLUSIONS

These data indicate that the inhibition of endogenous NO has a direct effect of increasing neutrophil sequestration in the pulmonary vasculature and alveoli. This suggests that endogenous NO plays a critical role in the control of neutrophil-endothelial cell interactions in the lung.

Effects of hydrazine derivatives on vascular smooth muscle contractility, blood pressure and cGMP production in rats: comparison with hydralazine

Hydralazine is a hydrazine derivative used clinically as a vasodilator and antihypertensive agent. Despite numerous studies with the drug, its mechanism of action has remained unknown; guanylate cyclase activation and release of endothelial relaxing factors are thought to be involved in its vasodilator effect. Other hydrazine derivatives are known to stimulate guanylate cyclase and could therefore share the vasodilator activity of hydralazine, although such possibility has not been assessed systematically. In the present study, hydralazine, hydrazine, phenylhydrazine, and isoniazid were evaluated for vascular smooth muscle relaxation in rat aortic rings with and without endothelium, as well as after incubation with the guanylate cyclase inhibitor methylene blue. They were also tested for enhancement of cyclic guanosine monophosphate (cGMP) production by cultured rat aortic smooth muscle cells and for hypotension in the anesthetized rat. All hydrazines relaxed aortic rings, an action unaffected by endothelium removal and, in all cases except hydralazine, antagonized by methylene blue. Only phenylhydrazine increased cGMP production and only hydralazine markedly lowered blood pressure. It was concluded that hydralazine vascular relaxation is independent of endothelium and is not related to guanylate cyclase activation. The other hydrazines studied also elicit endothelium-independent relaxation, but the effect is related to guanylate cyclase. The marked hypotensive effect of hydralazine contrasts with its modest relaxant activity and is not shared by the other hydrazines. The fact that hydrazine and isoniazid produce methylene blue-sensitive relaxation, yet do not enhance cGMP production suggests the need for activating factors present in aortic rings but not in isolated cells.

Nitric oxide synthase and hypertension

Nitric oxide, the metabolic product of L-arginine by the enzyme nitric oxide synthase, plays a pivotal role in the regulation of vascular homeostasis. Its complex interaction with the autocrine and paracrine systems, particularly angiotensin II, modulates vasoconstriction and vasodilatation as well as the architectural remodeling of the vascular bed. The major vascular hormones known to be involved are angiotensin II and endothelin-1. Upregulation of endothelin-1, a potent molecule, appears to be a consequence of the nitric oxide-angiotensin II imbalance that contributes to end-organ injury. Increased oxidative stress, common to different diseases including diabetes mellitus and hypertension, is also a determinant player in the interaction between angiotensin II and nitric oxide. The influence of a relative malfunction of the nitric oxide system on the vascular tone and vascular structure, and the effects of hypertension on this system, are discussed.