Hemodynamic effects of inducible nitric oxide synthase inhibition combined with sildenafil during acute pulmonary embolism

While endogenous nitric oxide (NO) may be relevant to the beneficial hemodynamic effects produced by sildenafil during acute pulmonary embolism (APE), huge amounts of inducible NO synthase (iNOS)-derived NO may contribute to lung injury. We hypothesized that iNOS inhibition with S-methylisothiourea could attenuate APE-induced increases in oxidative stress and pulmonary hypertension and, therefore, could improve the beneficial hemodynamic and antioxidant effects produced by sildenafil during APE. Hemodynamic evaluations were performed in non-embolized dogs treated with saline (n = 4), S-methylisothiourea (0.01 mg/kg followed by 0.5 mg/kg/h, n = 4), sildenafil (0.3 mg/kg, n = 4), or S-methylisothiourea followed by sildenafil (n = 4), and in dogs that received the same drugs and were embolized with silicon microspheres (n = 8 for each group). Plasma nitrite/nitrate (NOx) and thiobarbituric acid reactive substances (TBARS) concentrations were determined by Griess and a fluorometric assay, respectively. APE increased mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance index (PVRI) by 25 ± 1.7 mm Hg and by 941 ± 34 dyn s cm^?5 m^?2, respectively. S-methylisothiourea neither attenuated APE-induced pulmonary hypertension, nor enhanced the beneficial hemodynamic effects produced by sildenafil after APE (>50% reduction in pulmonary vascular resistance). While sildenafil produced no change in plasma NOx concentrations, S-methylisothiourea alone or combined with sildenafil blunted APE-induced increases in NOx concentrations. Both drugs, either alone or combined, produced antioxidant effects. In conclusion, although iNOS-derived NO may play a key role in APE-induced oxidative stress, our results suggest that the iNOS inhibitor S-methylisothiourea neither attenuates APE-induced pulmonary hypertension, nor enhances the beneficial hemodynamic effects produced by sildenafil.     

Hemodynamic and sympathoadrenal responses to mental stress during nitric oxide synthesis inhibition

Cardiovascular and sympathoadrenal responses to a reproducible mental stress test were investigated in eight healthy young men before and during intravenous infusion of the nitric oxide (NO) synthesis inhibitor N-monomethyl-L-arginine (L-NMMA). Before L-NMMA, stress responses included significant increases in heart rate, mean arterial pressure, and cardiac output (CO) and decreases in systemic and forearm vascular resistance. Arterial plasma norepinephrine (NE) increased. At rest after 30 min of infusion of L-NMMA (0.3 mg.kg(-1).min(-1) iv), mean arterial pressure increased from 98 +/- 4 to 108 +/- 3 mmHg (P <0.001) because of an increase in systemic vascular resistance from 12.9 +/- 0.5 to 18.5 +/- 0.9 units (P <0.001). CO decreased from 7.7 +/- 0.4 to 5.9 +/- 0.3 l/min (P <0.01). Arterial plasma NE decreased from 2.08 +/- 0.16 to 1.47 +/- 0.14 nmol/l. Repeated mental stress during continued infusion of L-NMMA (0.15 mg.kg(-1).min(-1)) induced qualitatively similar cardiovascular responses, but there was a marked attenuation of the increase in mean arterial blood pressure, resulting in similar "steady-state" blood pressures during mental stress without and with NO blockade. Increases in heart rate and CO were attenuated, but stress-induced decreases in systemic and forearm vascular resistance were essentially unchanged. Arterial plasma NE increased less than during the first stress test. Thus the increased arterial tone at rest during L-NMMA infusion is compensated for by attenuated increases in blood pressure during mental stress, mainly through a markedly attenuated CO response and suppressed sympathetic nerve activity.     

Role of nitric oxide in post-ischemic gingival hyperemia in anesthetized dogs

The possible involvement of nitric oxide (*NO) in the preservation of blood flow to the canine gingiva after compression of gingival tissue was studied. Gingival blood flow, gingival tissue oxygen partial pressure (PO2), external carotid arterial blood pressure and external carotid arterial blood flow were monitored before, during, and after compression of gingival tissue in the presence and absence of the nitric oxide synthase inhibitor, Nomega-nitro-L-arginine-methyl-ester (L-NAME). Compression of gingival tissue resulted in an immediate decrease in gingival blood flow and tissue PO2. After the compression of gingival tissue, hyperemia was observed in the gingiva, which depended on the duration of ischemia. Gingival tissue PO2 slowly recovered during hyperemia. Pretreatment with L-NAME (60 mg/kg, i.a.) significantly suppressed reactive hyperemia in gingival tissue. The L-NAME-suppressed reactive hyperemia was partially reversed by treatment with L-arginine (60 mg/kg, i.a.). In addition, *NO was detected using an *NO selective electrode during interruption of blood flow and during reactive hyperemia in the gingiva. These results suggest that *NO contributes to the vasodilation during reactive hyperemia in gingival tissue, and aids in the maintenance of homeostasis in gingival circulation.     

Hemodynamic actions of endothelin in conscious and anesthetized dogs

The newly described endogenous peptide, endothelin, was administered to five chronically instrumented conditioned dogs. Endothelin produced significant and simultaneous increases in both heart rate (HR) and mean arterial pressure (MAP) in conscious dogs. Endothelin also produced significant increases in MAP in anesthetized animals. Ganglionic suppression induced by hexamethonium (10 mg/kg) and atropine (0.1 mg/kg) blocked HR responses and markedly inhibited the pressor responses to endothelin in conscious animals. These results suggest that endothelin in part acts to elevate blood pressure and heart rate through modification of autonomic nervous system tone. When endothelin and angiotensin II were administered in mole equivalent doses, angiotensin II produced a pressor response of greater magnitude than did endothelin in conscious animals.     

Influence of renal denervation on renal effects of acute nitric oxide and ETA/ETB receptor inhibition in conscious normotensive rats.

The role of renal nerves in the effects of concomitant NO synthase and non-selective ET(A/)ET(B) receptor inhibition on renal function was investigated in conscious normotensive Wistar rats. NO synthase inhibition alone (10 mg/kg b. w. i.v. L-NAME) in sham-operated rats with intact renal nerves induced an increase in systolic, diastolic and mean arterial pressure, urine flow rate, sodium, chloride and calcium excretion (p<0.05). The effect of L-NAME was markedly reduced by bosentan (10 mg/kg b.w. i.v.) and the values of urine flow rate, sodium, chloride and calcium excretions returned to control level (p<0.05). L-NAME administration one week after a bilateral renal denervation increased blood pressure to a similar extent as in sham-operated rats but decreased urine flow rate (p<0.05) and did not change electrolyte excretion. ET(A/)ET(B) receptor inhibition with bosentan during NO synthase inhibition in the renal denervated rats did not produce changes in urine flow rate or electrolyte excretion. NO synthase inhibition as well as concurrent NO synthase and ET(A/)ET(B) receptor inhibition did not change clearance of inulin or paraaminohippuric acid in sham-operated or renal denervated rats. These results indicate that renal sympathetic nerves play an important modulatory role in NO and endothelin induced effects on renal excretory function.     

Hemodynamic effects of long-term converting-enzyme inhibition in renal hypertensive rats

The hemodynamic effects of a converting-enzyme inhibitor (CEI) given during 12 consecutive hours were studied in severe chronic renal hypertensive and normotensive Wistar rats. Hemodynamic parameters were obtained by thermodilution method in conscious unrestrained animals twenty-four hours after surgery. A bolus of CEI induced a significant decrease of mean arterial pressure (MAP) (from 192.2 +/- 8.2 to 163.3 +/- 5.9 mmHg, p less than 0.001) and total peripheral resistance (TPR) (from 7.69 +/- 0.53 to 5.83 +/- 0.33 mmHg.min/ml 100 g) in hypertensive animals. Cardiac index (CI) and heart rate increased significantly (p less than 0.05). Infusion of CEI to hypertensive animals during 12 consecutive hours produced a further progressive decrease in MAP and TPR (p less than 0.05) and an increase in CI (p less than 0.05). Heart rate did not change. Acute and prolonged infusions of CEI to normotensive group induced less but similar effect to those observed in hypertensive group. These results suggest that an increase of the renin-angiotensin system activity is the principal mechanism involved in the maintenance of high blood pressure during chronic phase of renal hypertension on the rats.     

Dose-dependent effects of nitric oxide synthase inhibition on systemic and renal hemodynamics in conscious lambs.

The present experiments were carried out to determine the role of nitric oxide in influencing systemic and renal hemodynamics in conscious young sheep. Parameters of cardiovascular function were measured before and for 4 h after intravenous injection of either L-NAME (NG-nitro-L-arginine methyl ester) or D-NAME (N(G)-nitro-D-arginine methyl ester) at doses of 10, 20, or 40 mg/kg in 13 conscious, chronically instrumented young sheep aged 43 +/-5 days. Blood pressure increased and heart rate decreased in a dose-dependent manner following administration of L-NAME. Renal vascular resistance was increased for 10 min following a dose of 10 mg/kg of L-NAME and for 120 min following a dose of 40 mg/kg of L-NAME. The renal vasodilatory response to close arterial injection of 1 microg/kg of acetylcholine was attenuated by L-NAME in a dose-dependent manner. These experiments provide the first information that under normal physiological conditions in conscious young animals, nitric oxide influences systemic and renal hemodynamics.     

Central respiratory effects of glutamine synthesis inhibition in dogs

Glutamic acid is an excitatory neurotransmitter that may have a significant role in the central chemical drive of ventilation. Therefore cardiorespiratory function was measured in pentobarbital sodium-anesthetized dogs before and after central inhibition of glutamate metabolism by means of methionine sulfoximine (MSO), a specific inhibitor of glutamine synthase (GS) catalyzing amidation of glutamate to glutamine. GS was inhibited centrally by perfusing the ventriculocisternal space with artificial cerebrospinal fluid (CSF) containing 92.5 mmol MSO per liter at a fixed pH, perfusion rate, and pressure. After GS inhibition, CSF transfer rate of [13N]glutamine synthesized from 13NH4+ amidation of glutamate was reduced five-fold, and minute ventilation increased from 2.90 +/- 0.41 (SE) l/min (0.164 +/- 0.020 l.min-1.kg body wt-1) to 4.46 +/- 0.52 l/min (0.254 +/- 0.029 l.min-1.kg body wt-1). This increase in ventilation with endogenous glutamate and the increase in ventilation previously observed during ventriculocisternal perfusion of exogenous glutamate are compared quantitatively via a model of central neurotransmitter glutamate chemoreception. The results support the hypothesis that the endogenous brain glutamate is important in the central chemical drive of ventilation.     

Role of glomerular nitric oxide in glycerol-induced acute renal failure

Myoglobinuric acute renal failure remains one of the least understood clinical syndromes and the mediators involved remain obscure. The aim of the present study was to assess the role of nitric oxide in glycerol-induced acute renal failure under normal conditions and after uninephrectomy. Acute renal failure was induced in rats by injection of 50% glycerol (10 mL x kg(-1) body weight). Half of the animals were subjected to uninephrectomy two days before glycerol injection. Two days after the induction of acute renal failure, glomeruli from some animals were isolated and glomerular nitrite production was measured. Another group of animals was used for acute clearance studies. In this case, the effect of infusing either L-NAME or L-arginine was assayed. Glomerular nitrite production was significantly decreased in glycerol-induced acute renal failure. Glomeruli from uninephrectomized animals showed an increase in nitrite production, both in normal conditions and after glycerol injection, as compared with glomeruli from non-nephrectomized animals. L-NAME infusion worsened renal function in all the study groups, but more slowly in animals with glycerol-induced acute renal failure than in control rats. In uninephrectomized animals L-NAME reduced renal function more than in animals with two kidneys. In conclusion, in this model of acute renal failure the decrease in glomerular nitric oxide production plays an important role in the decrease in renal function. After uninephrectomy, an increase in glomerular nitric oxide synthesis plays a protective role against glycerol-induced acute renal failure.     

Hemodynamic effects of sildenafil interaction with a nitric oxide donor compound in a dog model of acute pulmonary embolism

Sildenafil attenuates acute pulmonary embolism (APE)-induced pulmonary hypertension. However, the hemodynamic effects of sildenafil in combination with other vasodilators during APE have not been examined yet. In the present study, we examined the hemodynamic effects of combined diethylenetriamine/nonoate (DETA-NO, 1microMol kg(-1), i.v.) and sildenafil (0.25mg/kg, i.v.) in an anesthetized dog model of APE. Plasma nitrite/nitrate (NO(x)) and cyclic GMP concentrations were determined using an ozone-based chemiluminescence assay and a commercial enzyme immunoassay, respectively. We found that this dose of DETA-NO did not attenuate APE-induced pulmonary hypertension. However, significant decreases in mean pulmonary artery pressure were observed 15, 30 and 45min after the administration of sildenafil alone or after the combined administration of DETA-NO and sildenafil (all P<0.05). No significant differences among groups were observed in the respiratory parameters. While DETA-NO significantly increased NO(x) concentrations by approximately 4microM, cyclic GMP concentrations increased only when sildenafil was administered (all P<0.05). These results show that the combined administration of 1microMol kg(-1) of DETA-NO and sildenafil is not advantageous compared with sildenafil alone, thus suggesting that sildenafil alone produced maximum attenuation of APE-induced pulmonary hypertension, as far as the NO-cGMP pathway is concerned.     

Stimulatory effects of endogenous and exogenous nitric oxide on gastric acid secretion in anesthetized rats

We previously reported the stimulatory effect of endogenous nitric oxide (NO) on gastric acid secretion in the isolated mouse whole stomach and histamine release from gastric histamine-containing cells. In the present study, we investigated the effects of endogenous and exogenous NO on gastric acid secretion in urethane-anesthetized rats. Acid secretion was studied in gastric-cannulated rats stimulated with several secretagogues under urethane anesthesia. The acid secretory response to the muscarinic receptor agonist bethanechol (2 mg/kg, s.c.), the cholecystokinin(2) receptor agonist pentagastrin (20 microg/kg, s.c.) or the centrally acting secretagogue 2-deoxy-D-glucose (200 mg/kg, i.v.) was dose-dependently inhibited by the NO synthase inhibitor N(omega)-nitro-L-arginine (L-NNA, 10 or 50 mg/kg, i.v.). This inhibitory effect of L-NNA was reversed by a substrate of NO synthase, L-arginine (200 mg/kg, i.v.), but not by D-arginine. The histamine H(2) receptor antagonist famotidine (1 mg/kg, i.v.) completely inhibited the acid secretory response to bethanechol, pentagastrin or 2-deoxy-D-glucose, showing that all of these secretagogues induced gastric acid secretion mainly through histamine release from gastric enterochromaffin-like cells (ECL cells). On the other hand, histamine (10 mg/kg, s.c.)-induced gastric acid secretion was not inhibited by pretreatment with L-NNA. The NO donor sodium nitroprusside (0.3-3 mg/kg, i.v.) also dose-dependently induced an increase in acid secretion. The sodium nitroprusside-induced gastric acid secretion was significantly inhibited by famotidine or by the soluble guanylate cyclase inhibitor methylene blue (50 mg/kg, i.v.). These results suggest that NO is involved in the gastric acid secretion mediated by histamine release from gastric ECL cells.     

Neuroprotective effects of Ginkgo biloba extract in brain ischemia are mediated by inhibition of nitric oxide synthesis

We studied the effects of pre-treatment (15 days) with oral administration of Ginkgo biloba extract (Ph-Gb 37.5-150 mg/kg) on brain malonildialdehyde (MDA), brain edema, brain nitrite and nitrate and delayed neuronal death following transient cerebral ischemia in the Mongolian gerbil. Survival was not modified, however, pre-treatment with Ginkgo biloba significantly and in a dose-dependent way reduced post-ischemic brain MDA levels and post-ischemic brain edema. Delayed neuronal death in the CA1 of the hippocampus was attenuated by the highest dose of the extract. Increase of nitrite and nitrate was observed after cerebral ischemia in the hippocampus and it was dose-dependently reduced in animals pretreated with Ph-Gb, thus suggesting that neuroprotective effects of Ginkgo biloba may be due to an inhibitory action on nitric oxide formation.     

Nonspecific inhibition of nitric oxide synthesis evokes endothelin-dependent increases in myocardial contractility

The role of endogenous nitric oxide (NO) in modulating myocardial contractility is still unclear, in part because of unknown, secondary effects of blocking NO release. We hypothesized that the nonspecific inhibition of nitric oxide synthase (NOS) enhances endothelin-1 (ET-1) effects, which can play a role in ET-A receptor-dependent myocardial contractile responses. The myocardial contractility was estimated from the slope of the left ventricular end-systolic pressure–diameter relationship in closed-chest, pentobarbital-anesthetized dogs. Group 1 (n = 7) was the saline-treated control, while in groups 2 (n = 7) and 3 (n = 7) N-nitro-l-arginine (NNA, 4 mg kg^?1), a nonselective NOS blocker, was administered with or without pretreatment with the ET-A receptor antagonist ETR-P1/fl peptide (100 nmol kg^?1 iv). Plasma ET-1, nitrite/nitrate (NO_x) and blood superoxide levels were measured, and myocardial ET-1 content and xanthine oxidoreductase (XOR) activity were determined from myocardial biopsies. The infusion of NNA over 120 min decreased the plasma NO_x, significantly elevated the plasma ET-1 and blood superoxide levels, and in parallel greatly increased the left ventricular contractility as compared with the untreated controls [47.5 vs 30 mm Hg mm^?1]. The myocardial ET-1 content decreased simultaneously, while the XOR activity and blood superoxide level were significantly elevated. These effects, including NNA-induced positive inotropy, were significantly suppressed by pretreatment with ETR-P1/fl peptide. These results demonstrate that a diminished NO synthesis leads to a preponderant ET-1 effect, which increases myocardial contractility through an ET-A receptor-dependent mechanism.     

Catalase protects cardiomyocytes via its inhibition of nitric oxide synthesis.

Nitric oxide (NO) has been reported to play an important role as an effector molecule in cytokine signal transduction in cardiomyocytes. A treatment of neonatal rat ventricular cardiomyocytes with interleukin-1 beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) induces apoptosis via an NO-dependent pathway. However, cardiomyocytes were more resistant to NO-dependent cell death in the presence of catalase, while producing inducible nitric oxide synthase. This paper reports that catalase stimulates the NF-kappaB-binding affinity. However, the NO synthase activity is abolished by the addition of catalase, suggesting that H(2)O(2) is involved in NO synthesis in a posttranslation state. The catalase-induced inhibition of NO was partially but significantly reversed by H(4)B, an important cofactor of NO synthesis. Treatment of myocytes with IL-1beta, TNF-alpha, and IFN-gamma induced a significant increase in the formation of peroxynitrite, and a pretreatment with catalase was found to quench the production of peroxynitrite. This paper shows that the catalase activity was significantly down-regulated by H(4)B in a concentration-dependent manner. The treatment of H(4)B induced reactive oxygen species (ROS) release in cardiac cell system. These results suggest that catalase interferes with NO and peroxynitrite production as well as with the related apoptosis of cardiomyocytes. This study also shows that the catalase-induced inhibition of NO release may be reversed by H(4)B by the release of ROS.     

胍基丁胺对大鼠血流动力学的影响及其细胞机制

在麻醉大鼠研究静注胍基丁胺（ＡＧＭ）对血流动力学的影响,并初步探讨其机制。结果如下：（１）静注ＡＧＭ（１０ｍｇ／ｋｇ）后,ＨＲ,ＭＡＰ,ＬＶＰ,±ＬＶｄｐ／ｄｔｍａｘ,ＣＩ和ＴＰＲＩ均明显下降;（２）预先静注ＮＯＳ抑制剂ＬＮＮＡ（１５ｍｇ／ｋｇ）或腹腔内注射鸟苷酸环化酶抑制剂亚甲基蓝（５０ｍｇ／ｋｇ）,均不能阻断ＡＧＭ的降压作用;（３）预先静注咪唑啉受体和α２肾上腺素能受体阻断剂ｉｄａｚｏｘａｎ（２ｍｇ／ｋｇ）则可明显阻抑ＡＧＭ的降压效应。以上结果表明,ＡＧＭ对麻醉大鼠的降压机制,在于显著抑制心肌收缩性而使心输出量降低,以及舒张外周血管致使总外周阻力下降;此效应似主要由ＩＲ和／或α２ＡＲ所介导。     

Effects of nitric oxide synthesis inhibition with or without nitric oxide inhalation on responses to systemic cocaine administration in rats

The effects of N^ω-nitro-L-arginine methyl ester (L-NAME) i.v. and nitric oxide (NO) inhalation on integrated systemic responses to cocaine were studied in lightly anesthetized, paralyzed, and mechanically ventilated rats. Cocaine (4 mg/kg/min i.v.) produced seizures then isoelectric electrocephalographic (isoEEG) activity as well as an initial increase in systolic blood pressure and heart rate, then progressive cardiovascular system depression culminating in asystole. Pretreatment with L-NAME (2 mg/kg/min i.v.) for 30 min significantly reduced the incidence of seizure as compared to saline treated animals (saline 7/8; L-NAME 3/8). Doses of cocaine that produced arrhythmias, isoEEG and asystole were significantly lower in the L-NAME treated animals as compared to the saline group. L-NAME did not affect peak systolic blood pressure and heart rate responses to cocaine. NO inhalation (80 ppm) did not affect CNS and cardiovascular responses to cocaine in control animals but enhanced the effects of L-NAME on cocaine toxicity. The results show that pretreatment with L-NAME reduces the central nervous system stimulatory effect of cocaine (reduced seizure incidence) and enhances its depressant effect on both the central nervous system (lower does for isoEEG) and the cardiovascular system (lower dose for arrhythmias and asystole), but does not affect the cardiovascular stimulatory action of cocaine. NO inhalation does not protect against any of the systemic effects of cocaine in animals with normal or suppressed NO production.     

Direct and reflexive effects of nitric oxide synthase inhibition on blood pressure

Direct effects of vasoactive substances on blood pressure can be examined in individuals with tetraplegia due to disruption of descending spinal pathways to sympathetic preganglionic neurons, as cervical lesions interfere with baroreceptor reflex buffering of sympathetic outflow. In this study, we assessed effects of the nitric oxide synthase inhibitor nitro-L-arginine methyl ester (L-NAME) on mean arterial pressure, heart rate, and plasma norepinephrine concentrations in individuals with tetraplegia vs. effects shown in a neurologically intact control group. Seven individuals with tetraplegia and seven age-matched controls received, on separate visits and in the following order, placebo (30 ml normal saline) and 0.5, 1, 2, and 4 mg/kg L-NAME intravenously over 60 min. Supine hemodynamic data were collected, and blood was sampled at the end of each infusion and at 120, 180, and 240 min thereafter. L-NAME increased mean arterial pressure, and the relative increase was greater in the tetraplegia group than in the control group. Heart rate was reduced after L-NAME administration in both groups. L-NAME decreased plasma norepinephrine in the control group but not in the group with tetraplegia. These findings suggest that reflexive sympathoinhibition normally buffers the pressor response to nitric oxide synthase inhibition, an effect that is not evident in individuals with tetraplegia as a result of decentralized sympathetic vasomotor control.