EFFECTS OF CHRONIC NICOTINE INGESTION ON PRESSOR RESPONSE TON-NE2RO-L-ARGININE METHYL ESTER ANDEX VIVOCONTRACTION AND RELAXATION RESPONSE OF AORTA TOL-ARGININE

Effects of nitric oxide synthase inhibition on blood vessels were studied in nicotine-treated rats. Male Sprague–Dawley rats drank a nicotine solution with a concentration of 25 or 50 μg/ml for 15 days. The blood pressure and heart rate of chloralose-anaesthetized rats and isolated aortic strip contractions were measured.N^ωNitro-L-arginine methyl ester (L-NAME)-induced hypertension was significantly reduced after chronic nicotine treatment. TheE_maxof contractions of isolated aortic strips to noradrenaline were dose-dependently enhanced by nicotine and the potentiation was abolished byL-arginine. The relaxation of aortic strips to acetylcholine was significantly decreased in nicotine-treated rats, whereasL-arginine, but notD-arginine, reversed this action. Neither nicotine norL-NAME affected the heart rate. The results show that chronic nicotine treatment reduced the pressor response ofL-NAME.     

Alteration by cadmium of rat submandibular gland secretory function and the role of the -arginine/nitric oxide pathway

The effects of cadmium, -arginine (nitric oxide precursor) and N^ω-nitro- -arginine methyl ester ( -NAME) as a nitric oxide synthesis inhibitor and cotreatment of them on rat submandibular secretory function were studied. Pure submandibular saliva was collected intraorally by micro polyethylene cannula from anaesthetized rats using pilocarpine as secretagogue. Fourteen days treatment with 10 mg l⁻¹cadmium as cadmium chloride in drinking water caused significant alterations on salivary function. Salivary flow rate, total protein concentration and amylase activity of saliva were decreased while secretion of calcium was increased by cadmium. Two weeks treatment of rats with -arginine (2.25%) in drinking water caused an increase in submandibular gland weight. Flow rate was reduced by -NAME. The total protein concentration of saliva was increased by -arginine while decreased by -NAME. Calcium concentration of saliva was reduced by -arginine and increased by -NAME. Cotreatment of cadmium with -arginine prevented cadmium-induced reduction of flow rate while -NAME cotreatment potentiated cadmium-induced reduction of flow rate. -arginine showed a preventive effect on cadmium-induced decrease of protein concentration and reached control levels. -arginine potentiated cadmium-induced increase of saliva calcium concentration. It is confirmed that nitric oxide (NO) has a role in salivary gland function. It is also concluded that cadmium inhibitory effects on salivary gland function are modulated by the NO system as it is observed that the cadmium inhibitory effect on submandibular gland function is diminished by -arginine and extended by -NAME. Considering the properties of cadmium substitution for calcium in many intracellular events, different types of alterations can be discussed.     

Aortic Remodelling in Chronic Nicotine-Administered Rat

Vascular remodelling is an adaptive mechanism, which counteracts pressure changes in blood circulation. Nicotine content in cigarette increases the risk of hypertension. The exact relationship between nicotine and vascular remodelling still remain unknown. Current study was aimed to determine the effect of clinically relevant dosage of nicotine (equivalent to light smoker) on aortic reactivity, oxidative stress markers and histomorphological changes. Twelve age-matched male Sprague-Dawley rats were randomly divided into two groups, i.e.: normal saline as control or 0.6 mg/kg nicotine for 28 days (i.p., n=6 per group). On day-29, the rats were sacrificed and the thoracic aorta was dissected immediately for further studies. Mean arterial pressure (MAP) and pulse pressure (PP) of nicotine-treated vs. control were significantly increased (p<0.05). Nicotine-treated group showed significant (p<0.05) increase tunica media thickness, and decrease in lumen diameter, suggesting vascular remodelling which lead to prior hypertension state. The phenylephrine (PE)-induced contractile response in nicotine group was significantly higher than control group (ED₅₀=1.44×10⁵ M vs. 4.9×10⁶ M) (p<0.05~0.001). However, nicotine-treated rat showed significantly lower endothelium-dependent relaxation response to acetylcholine (ACh) than in control group (ED₅₀=6.17×10⁷ M vs. 2.82×10⁷ M) (p<0.05), indicating loss of primary vascular function. Malondialdehyde (MDA), a lipid peroxidation marker was significantly higher in nicotine group. Superoxide dismutase (SOD) enzymatic activity and glutathione (GSH) were all reduced in nicotine group (p<0.05) vs. control, suggesting nicotine induces oxidative imbalance. In short, chronic nicotine administration impaired aortic reactivity, probably via redox imbalance and vascular remodelling mechanism.     

Protective effect of oral -arginine administration on gentamicin-induced renal failure in rats

We investigated the effects of orally supplemented -arginine, the substrate of nitric oxide (NO) and N^ω-nitro- -arginine methyl ester ( -NAME), a nitric oxide-synthase inhibitor in gentamicin-induced renal failure. Rats were given gentamicin (100 mg/kg/day s.c.), gentamicin and -arginine (2 g/l, drinking water), gentamicin and -NAME (100 mg/l, drinking water) or gentamicin plus -arginine and -NAME. After 8 days, the gentamicin group developed marked renal failure, characterized by a significantly decreased creatinine clearance and increased blood creatinine, fractional excretion of sodium, fractional excretion of lithium, urine gamma glutamyl transferase, systolic blood pressure and daily urine volume when compared to controls. Renal histological analysis confirmed tubular necrosis. -arginine administration caused normalization of these parameters, whereas -NAME led to aggravation of the failure. Concomittant administration of -NAME and -arginine to gentamicin-treated rats caused no significant changes when compared to the rats receiving gentamicin alone. We conclude that -arginine supplementation has beneficial effects in gentamicin-induced renal failure in rats and that these effects are reversed by the NO-synthase inhibitor, -NAME.     

Bombesin-induced contractions of guinea pig lung strips are modulated by endogenous nitric oxide

We have investigated the effects of a nitric oxide (NO) biosynthesis inhibitor N^\sw-nitro-L-arginine methyl ester (l-NAME) on the bombesin-evoked contraction of guinea pig parenchymal lung strips. The bombesin-induced contractions of lung strips were significantly increased after l-NAME (300 M) pre-treatment. The maximal response was increased (P < 0.01) by 37% after l-NAME treatment when compared with the control group. The pD₂ value was not influenced by l-NAME pre-treatment. The enhancement of the bombesin-induced contraction caused by l-NAME was reversed by addition of an excess of the NO precursor-l-arginine (600 M) but not by the addition of its inactive enantiomer d-arginine (600 M). Like l-NAME, methylene blue (1 M), an agent that inhibits the soluble guanylyl cyclase activated by NO, significantly increased (P < 0.01) the maximal contraction induced by bombesin (183 ± 16 mg) when compared with the control group (141 ± 15 mg). When tested against other agonist-induced contractions, l-NAME did not change the responsiveness of parenchymal lung strips to bradykinin or carbachol but significantly increased the lung contraction induced by histamine. NO synthesis inhibition resulted in a pronounced increase in the bombesin-induced contraction of guinea-pig lung strips. Our results suggest that bombesin contributes to NO synthesis and release which then acts to reduce the contraction of the lungstrip in response to bombesin.     

Reduced nitric oxide formation causes coronary vasoconstriction and impaired dilator responses to endogenous agonists and hypoxia in dogs

We investigated the relative contribution of basal and agonist stimulated EDRF/NO release to the adjustment of coronary tone and myocardial perfusion in conscious dogs by inhibiting coronary endothelial NO formation with N^G-nitro-l-arginine methyl ester (l-NAME). Chronically instrumented conscious dogs (n = 9) were prepared for measurement of mean arterial blood pressure (MAP), heart rate (HR), coronary blood flow (CF) and diameter of the left circumflex (CD_LC) and left anterior descending (CD_LAD) coronary artery, respectively. Intracoronary infusions of l-NAME (30.3 mM; 0.25 ml × min^–1) caused significant increases in MAP and decreases in HR. CD_LC decreased by 3.8% from 3.01 ± 0.04 to 2.90±0.04 mm and CF decreases by 30% from 12.9 ± 0.2 to 9.1 ± 0.2 (aU). Peak reactive hyperemia (CF_max) evoked by 20-s-lasting occlusions of the left circumflex coronary artery decreased from 29.9 ± 0.8 to 25.8 ± 1.0 aU and maximal flow-dependent coronary dilation were reduced from 2.04 ± 0.08 to 0.91±0.12% after inhibition of NO-synthesis. Intracoronary infusions of acetylcholine (ACh), Adenosinc (Ado), bradykinin (Bk), and papaverine (Pap) caused dose-dependent increases in CD_LC and CE Infusion of l-NAME nearly abolished the dilator effect of Ado on CD_LC and reduced those to ACh, Bk and Pap. Increases in CF to ACh, Ado and Bk but not to Pap were reduced by l-NAME. Subsequent intracoronary infusions of l-arginine (303 mM; 0.25 ml × min^–1) reduced l-NAME-induced CF-changes partly, but did not reverse coronary constriction. These results suggest that inhibition of the continuous release of nitric oxide markedly reduces myocardial perfusion in vivo. Endogenous dilator mechanisms are likewise impaired. Thus, in the heart, nitric oxide deficiency probably cannot be fully compensated for by counter-regulating mechanisms. Correspondence to: E. Bassenge at the above address     

一氧化氮合酶抑制剂(L-NAME)的药理作用与慢性血管效应

目的：探讨N^ω-硝基L-精氨酸甲酯(L-NAME)对不同动脉的慢性血管效应及其与抑制内皮依赖性一氧化氮(EDNO)合成的关系。方法：采用大鼠离体动脉环的张力测定,一氧化氮合酶活性测定及组织学、生化学等方法。结果：给药8周后大鼠尾动脉压明显升高、体重及胸主动脉的内皮依赖性舒张功能明显下降并释放内皮依赖性收缩因子,肠系膜微动脉的内皮依赖性舒张功能无改变。给药8周后出现了动脉中膜肥厚及其周围纤维化。N^ω-硝基D-精氨酸甲酯(D-NAME)的慢性给药亦可引起与L-NAME同样的动脉周围纤维化。结论：L-NAME对大鼠胸主动脉及肠系膜微动脉的作用不同,其慢性血管效应与抑制EDNO合成以外的其它机制相关。     

URINARY NO3− EXCRETION AS AN INDICATOR OF NITRIC OXIDE FORMATION IN VIVO DURING ORAL ADMINISTRATION OF l-ARGININE OR l-NAME IN RATS

• 1 Endothelium-derived nitric oxide (NO), a major modulator of vascular tone, is synthesized from the terminal guanidino nitrogen of l -arginine. This reaction is inhibited by analogues of l -arginine, such as N-nitro-l -arginine methyl ester (l -NAME). Many of the biological effects of NO are mediated by the second messenger cGMP. NO is rapidly oxidized to NO₃^? which, like cGMP, is eliminated via excretion into the urine. In a placebo controlled study, we investigated whether oral bolus administration of l -arginine and l -NAME affects the urinary excretion rates of NO₃^? and cGMP in Munich Wistar Frömmter (MWF) rats.
• 2 Twenty MWF rats were kept in metabolic cages and received l -arginine (3 g/kg body weight), l -NAME (50mg/kg), or placebo (0.9% saline) in randomized order. Urine samples were sequentially collected for 10 h and analysed for creatinine, NO₃^? and cGMP.
• 3 l -Arginine induced a slight, but prolonged increase in urine flow, whereas l -NAME induced an early, transient increase in urine flow which was followed by a decrease. Creatinine clearance decreased by 65% after l -NAME, but was not affected by l -arginine or placebo.
• 4 Urinary NO₃^? and cGMP excretion rates transiently increased after l -arginine (NO₃^?: + 29%; cGMP: + 16%) for 4–5h, whereas l -NAME induced an immediate, pronounced and lasting inhibition of urinary NO₃^? and cGMP excretion (NO₃^?:-76%; cGMP:-46%). Urinary NO₃^? and cGMP excretions were significantly correlated (r = 0.755; P< 0.001).
• 5 Urinary excretion rates of NO₃^? and cGMP, expressed as μmol/h, were correlated to urine flow (mL/h; r = 0.617 and 0.649, respectively; both P<0.05), whereas after correction by urinary creatinine (μmol/mmol creatinine) no correlation with urine flow was observed, indicating that these excretion rates were independent of renal excretory function. Thus we conclude that changes in the urinary excretion rates of NO₃^? and cGMP represent changes in NO production rates in vivo when expressed in relation to urinary creatinine. Urinary NO₃^? and cGMP excretion is modulated by acute NO synthase inhibition or substrate provision.

     

Differential effect of L-NAME and S-methyl-isothiourea on leukocyte emigration in carrageenin-soaked sponge implants in rat

1. The role of nitric oxide (NO) in leukocyte (polymorphonuclear cells, monocytes and lymphocytes) emigration was studied in a model of carrageenin-sponge implants in rats.
2. The subcutaneous implantation of 1% (w/v) of λ-carrageenin-soaked sponges elicited an inflammatory response that was characterized by a time-related increase in leukocyte infiltration in the sponges and increased levels of nitrite in the exudate. Total leukocyte infiltration and nitrite production were maximal at 24 h and decreased after 48 and 96 h. The mononuclear cell influx was maximal at 48 h (21% of the total leukocytes). Therefore, this time point was used in the successive experiments.
3. Polymorphonuclear cell (PMN) and lymphocyte infiltration in the sponges significantly increased when rats were treated with the non-specific NO-synthase (NOS) inhibitor, N^G-nitro-L-arginine methylester (L-NAME) (1 mg ml⁻¹ in drinking water ad libitum). Monocyte emigration was not affected by L-NAME treatment. The nitrite levels in the exudate of L-NAME-treated rats were significantly reduced. The concomitant ingestion of L-arginine (30 mg ml⁻¹) resulted in a reversion of the L-NAME effect, while D-arginine (30 mg ml⁻¹) had no effect, indicating the involvement of the L-arginine: NO pathway.
4. Administration of L-NAME resulted also in an increased release of tumour necrosis factor-α (TNF-α) and prostacyclin (measured as the stable metabolite, 6-keto-PGF_1α). L-NAME had no effect on monocyte chemoattractant protein-1 (MCP-1) release in the exudate.
5. Since L-NAME may have effects on the local blood flow, phenylephrine (0.034 mg ml⁻² in drinking water) was used as it has an effect on the local blood flow similar to L-NAME. Phenylephrine had no effect on either leukocyte emigration, or on nitrite, TNF-α, prostacyclin or MCP-1 accumulation in the exudate.
6. In contrast, the more selective iNOS inhibitor S-methyl-isothiourea (SMT) (10 μg ml⁻¹ in drinking water) significantly reduced PMNs and lymphocyte influx in the sponge, having no effect on monocyte influx. Moreover, SMT decreased nitrite production in the exudate to a comparable extent as L-NAME.
7. Administration of SMT significantly reduced MCP-1 release in the exudate, without an effect on TNF-α or prostacyclin production. Moreover SMT did not produce any changes in local blood flow.
8. Our results show that a different outcome of the inflammatory process can be obtained depending on the types of NOS inhibitor used.

     

EFFECTS OF NITRIC OXIDE SYNTHASE INHIBITION AND ENDOTHELIN ETA RECEPTOR BLOCKADE ON HAEMODYNAMICS IN HYPERTENSIVE RATS

1. The objectives of the present study were to study regional differences in haemodynamics between spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats induced by the nitric oxide synthase (NOS) inhibitor N^G-monomethyl -l -arginine (l -NMMA) and the endothelin ET_A receptor antagonist BQ123 in vivo in tissues known to be important for blood pressure (BP) regulation (heart, kidney and skeletal muscle). Furthermore, the effect of acetylcholine (ACh) infusion (2 μg/kg per min) was examined after l -NMMA or BQ 123. The microsphere method was used for determinations of cardiac index (CI) and regional haemodynamics. 2. N^G-Monomethyl-l -arginine (20mg/kg) increased BP (26–48%; P < 0.01) and reduced CI in both rat strains. BQ 123 (1 mg/kg) reduced BP slightly (-4 to 11 %; P < 0.05). 3. N^G -Monomethyl-l -arginine significantly increased myocardial and skeletal muscle vascular resistance in SHR only; however, in the kidney, l -NMMA reduced blood flow and increased vascular resistance in both rat strains. 4. BQ 123 induced minor changes in regional haemodynamics that were not significantly different between the two strains. 5. Acetylcholine following BQ123 induced an increase in myocardial blood flow in WKY rats, but decreased blood flow in SHR. Acetylcholine following l -NMMA reduced myocardial blood flow in both strains. 6. Acetylcholine following BQ 123 induced renal vasodilation in WKY rats but, following l -NMMA, ACh did not induce renal vasodilation in either rat strain. In contrast, l -NMMA did not abolish the vasodilation of acetylcholine in skeletal muscle in WKY rats. 7. In conclusion, the contribution of nitric oxide to basal vessel tone was not impaired in the heart, skeletal muscle and kidney in SHR. Antagonism of ET_A receptors caused similar haemodynamic responses in both rat strains in these organs. Furthermore, NOS inhibition, but not ET_A blockade, blunted the expected ACh-induced vasodilation in the heart and kidney in WKY rats, but not in skeletal muscle in both strains.     

Involvement of NO/cGMP pathway in toluene-induced locomotor hyperactivity in female rats

Rationale Nitric oxide (NO) is implicated in the acute locomotor activating effects of some addictive drugs such as amphetamine, caffeine, and PCP, but has not been investigated in the case of toluene.Objectives This study determined the contribution of the NO-cyclic GMP (cGMP) pathway to locomotor stimulant effects of toluene.Methods Locomotor activity was measured for 90 min immediately following toluene (500–1,000 mg/kg, IP) or corn oil treatments in Sprague-Dawley female rats. A NO generator, sodium nitroprusside (SNP) (3 and 6 mg/kg), a NO precursor, l-arginine (l-Arg) (250 mg/kg), a NO synthase inhibitor,N^G-nitro-l-arginine methyl ester (l-NAME) (5–20 mg/kg, IP), and a soluble guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 mg/kg) were injected 5 min before toluene (750 mg/kg, IP) treatment. The combination effects of SNP with l-NAME, l-arginine with l-NAME, SNP with ODQ and l-arginine with ODQ on toluene-induced locomotor hyperactivity were also determined.Results The locomotor hyperactivity induced by toluene was significantly inhibited by SNP and l-arginine, but enhanced by l-NAME and ODQ. SNP and l-arginine completely reversed the combined effects of l-NAME and toluene to a basal level and abolished the enhancing effects of ODQ.Conclusions The results suggested that NO/cGMP-dependent mechanism might be involved in toluene-induced locomotor activity in rats.     

EFFECT OF EARLY BLOCKADE OF BRADYKININ B2-RECEPTORS ON THE BLOOD PRESSURE PHENOTYPE OF NORMOTENSIVE AND SPONTANEOUSLY HYPERTENSIVE RATS

We evaluated if chronic blockade of bradykinin B₂-receptors by the long-acting antagonist Icatibant (D-Arg,‘Hyp³,Thi⁵,D-Tic⁷,Oic⁸’-bradykinin) affects blood pressure of rats. Pairs of normotensive Wistar Kyoto rats or spontaneously hypertensive rats were mated and their offspring received Icatibant (25 nmol day⁻¹per kg body wt., s.c.) or vehicle from the 2nd day until the 7th week of life. Then, the administration of Icatibant or vehicle was continued by i.p. infusion using Alzet osmotic pumps. At 9 weeks of age, normotensive rats given Icatibant showed greater systolic blood pressure (135±1vs115±1 mmHg in vehicle-treated rats,P<0.01), while heart rate was similar. The group difference regarding blood pressure levels was confirmed by direct intra-arterial measurement. No difference was detected between vehicle- and Icatibant-treated spontaneously hypertensive rats regarding blood pressure increase with aging. In conclusion, chronic blockade of bradykinin receptors by Icatibant alters the adult cardiovascular phenotype of Wistar Kyoto rats, provided that the antagonist is given at the early phases of life. These results suggest that the B₂-receptor is essential for the maintenance of cardiovascular homeostasis during development, whereas it does not exert a protective role against the progression of hypertension in a rat model of genetic hypertension.     

Antioxidant and vascular protective effects of curcumin and tetrahydrocurcumin in rats with <Emphasis Type="SmallCaps">l</Emphasis>-NAME-induced hypertension

Inhibition of nitric oxide synthesis with N ^ω -nitro-l-arginine methyl ester (l-NAME) induces marked hypertension and oxidative stress. Curcumin (CUR) has been shown strong antioxidant property. Tetrahydrocurcumin (THU), a major metabolite of CUR, possesses several pharmacological effects similar to CUR; however, it is less studied than CUR. We investigated whether CUR and THU could prevent vascular dysfunction and inhibit development of hypertension in l-NAME-treated rats. Male Sprague–Dawley rats were administered with l-NAME (50 mg/kg/day) in drinking water for 3 weeks. CUR or THU (50 and 100 mg/kg/day) was fed to animals simultaneously with l-NAME. l-NAME administration induced increased arterial blood pressure and elevated peripheral vascular resistance accompanied with impaired vascular responses to angiotensin II and acetylcholine. CUR and THU significantly suppressed the blood pressure elevation, decreased vascular resistance, and restored vascular responsiveness. The improvement of vascular dysfunction was associated with reinstating the marked suppression of eNOS protein expression in the aortic tissue and plasma nitrate/nitrite. Moreover, CUR and THU reduced vascular superoxide production, decreased oxidative stress, and increased the previously depressed blood glutathione (GSH) and the redox ratios of GSH in l-NAME hypertensive rats. The antihypertensive and some antioxidant effects of THU are apparently more potent than those of CUR. This study suggests that CUR and THU prevented the development of vascular dysfunction induced by l-NAME and that the effects are associated with alleviation of oxidative stress.     

A STUDY OF ANGIOTENSIN II RECEPTORS AFTER CHRONIC INHIBITION OF NITRIC OXIDE SYNTHASE IN THE SPONTANEOUSLY HYPERTENSIVE RAT

1. Nitric oxide (NO) synthase inhibition, induces a sustained increase in blood pressure and amplifies the pressor response to infused angiotensin II (AngII). This study was designed to investigate the contribution of AngII receptors to the elevated blood pressure and enhanced pressor response to AngII in the spontaneously hypertensive rat (SHR) chronically treated with N^G-nitro-l -arginine-methyl ester (l -NAME). 2. Two groups of 13 week old female SHR were housed four to a box. Group I rats received l -NAME for 7 days (2.5 mg/kg per day) in their drinking water. Group II rats received water only. Blood pressure was monitored daily by tail-cuff plethysmography. Plasma AngII was measured by radioimmunoassay. Aortic and uterine receptor binding was determined by saturation analysis using [¹²⁵I]-Sar⁸, Ile¹)AngII. Data was analysed using the computer program ligand. 3. Mean systolic blood pressure was significantly elevated in rats treated with l -NAME compared with the control group. Plasma AngII concentration was slightly decreased in rats treated with l -NAME compared with control. Densities of both aortic and uterine AngII receptors increased significantly following NO synthase inhibition. Receptor affinity in the aorta decreased in the l -NAME group compared with control. However, uterine AngII receptor affinity was unchanged. 4. We conclude that the increased blood pressure and enhanced pressor responsiveness that occurs with chronic inhibition of NO synthesis may result partly from increased vascular AngII receptor expression.     

Alteration of flow-induced dilatation in mesenteric resistance arteries of L-NAME treated rats and its partial association with induction of cyclo-oxygenase-2

1. We investigated the response to pressure (myogenic tone) and flow of rat mesenteric resistance arteries cannulated in an arteriograph which allowed the measurement of intraluminal diameter for controlled pressures and flows. Rats were treated for 3 weeks with N^G-nitro-L-arginine methyl ester (L-NAME, 50 mg kg⁻¹ day⁻¹) or L-NAME plus the angiotensin I converting enzyme inhibitor (ACEI) quinapril (10 mg kg⁻¹ day⁻¹).
2. Mean blood pressure increased significantly in chronic L-NAME-treated rats (155±4 mmHg, n=8, vs control 121±6 mmHg, n=10; P<0.05). L-NAME-treated rats excreted significantly more dinor-6-keto prostaglandin F_1α (dinor-6-keto PGF_1α), the stable urinary metabolite of prostacyclin, than control rats. The ACEI prevented the rise in blood pressure and the rise in urinary dinor-6-keto PGF_1α due to L-NAME.
3. Isolated mesenteric resistance arteries, developed myogenic tone in response to stepwise increases in pressure (42±6 to 847±10 mN mm⁻¹, from 25 to 150 mmHg, n=9). Myogenic tone was not significantly affected by the chronic treatment with L-NAME or L-NAME+ACEI.
4. Flow (100 μl min⁻¹) significantly attenuated myogenic tone by 50±6% at 150 mmHg (n=10). Flow-induced dilatation was significantly attenuated by chronic L-NAME to 22±6% at 150 mmHg (n=10, P=0.0001) and was not affected in the L-NAME+ACEI group.
5. Acute in vitro N^G-nitro-L-arginine (L-NOARG, 10 μM) significantly decreased flow-induced dilatation in control but not in L-NAME or L-NAME+ACEI rats. Both acute indomethacin (10 μM) and acute NS 398 (cyclo-oxygenase-2 (COX-2) inhibitor, 1 μM) did not change significantly flow-induced dilatation in controls but they both decreased flow-induced dilatation in the L-NAME and L-NAME+ACEI groups. Acute Hoe 140 (bradykinin receptor inhibitor, 1 μM) induced a significant contraction of the isolated mesenteric arteries which was the same in the 3 groups.
6. Immunofluorescence analysis of COX-2 showed that the enzyme was expressed in resistance mesenteric arteries in L-NAME and L-NAME+ACEI groups but not in control. COX-1 expression was identical in all 3 groups.
7. We conclude that chronic inhibition of nitric oxide synthesis is associated with a decreased flow-induced dilatation in resistance mesenteric arteries which was compensated by an overproduction of vasodilator prostaglandins resulting in part from COX-2 expression. The decrease in flow-induced dilatation was prevented by the ACEI, quinapril.

     

EFFECTS OF CHRONIC ETHANOL CONSUMPTION ON α-ADRENERGIC-INDUCED CONTRACTIONS AND ENDOTHELIUM-DEPENDENT RELAXATIONS IN RAT THORACIC AORTA

The effects of chronic oral administration of ethanol (7.2% daily during 24 weeks) on the contractions induced by phenylephrine (Phe) and the endothelium-dependent relaxation responses to acetylcholine (ACh) were studied in rat thoracic aorta. Ethanol pretreatment significantly attenuated the contractile responses to Phe, resulting in parallel shift of the concentration–response curve to the right. EC₅₀values of Phe were 64.6±11.2 and 95.5±8.5 nmol l⁻¹in control and ethanol-fed rats, respectively. On the other hand, either calcium-induced contractions or relaxation responses to ACh and sodium nitroprusside were similar in the vessels of the control and ethanol-treated rats. These results suggest that chronic ethanol ingestion significantly attenuates the α₁-adrenergic-induced contractions but does not affect the relaxation responses mediated by nitric oxide in rat aortic rings.     

STUDIES ON THE SPASMOLYTIC AND UTERINE RELAXANT ACTIONS OF N -ETHYL AND N -BENZYL-1,2-DIPHENYL ETHANOLAMINES: ELUCIDATION OF THE MECHANISMS OF ACTION

The influence of N -ethyl- and N -benzyl-1,2-diphenyl ethanolamines (compounds E and B, respectively) was examined on the spontaneously contracting rabbit jejunum and the rat uterus together with their influence on the contractions induced by some spasmogens in the guinea-pig ileum and oxytocics and CaCl₂in the pregnant rat uterus. Both E and B inhibited the spontaneous contractions of the rabbit jejunum with ID₅₀values of 0.13 and 0.03 μmol ml⁻¹. Their inhibitory activities were not antagonized by α- or β-adrenoceptor blockers but significantly reversed by CaCl₂(0.015 μmol ml⁻¹). The compounds also antagonized nicotine, ACh-, histamine-, 5-HT- and CaCl₂-induced contractions by 44–100%. Compound E seemed to be several times more potent than B in inhibiting the spontaneous uterine contractions with an ID₅₀of (7 nmol ml⁻¹). Their inhibitory effects were not antagonized by β₂-adrenoceptor or H₂-receptor blocking drugs. Both compounds (40 nmol ml⁻¹) antagonized in a competitive manner CaCl₂-induced contractions in the K⁺-depolarised uterus and PGE₂and oxytocin-induced uterine contractions. The ID₅₀values were in the range of 1.6–10.7 nmol ml⁻¹. The results suggest that E and B compounds may be considered as putative L-Ca²⁺channel blockers with certain selectivities. The E compound seemed to be more selective against uterine L-Ca²⁺channels and the B compound against intestinal smooth muscles. Thus, the compounds may be of potential value in treatment of some colics, the irritant bowel syndrome, dysmenorrhoea and premature deliveries. 1999 Academic Press@p$hr     

Scavenging of hydroxyl radicals but not of peroxynitrite by inhibitors and substrates of nitric oxide synthases

1. The nitric oxide synthase inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) is widely used to study the role of NO^• in physiological and pathological processes, including its role in the generation of the cytotoxic species peroxynitrite (ONOO⁻) and of reactive oxygen radicals such as hydroxyl (OH^•). Often L-NAME is applied to tissues at mM concentrations. At such high concentrations, it might act as a free radical scavenger. A similar possibility might apply to the use of high levels of arginine to study the role of NO^. in atherogenesis.
2. We therefore examined the rate of scavenging of OH^• by L-NAME and found that L-NAME reacts more quickly with OH^. than the established ‘OH^. scavenger'' mannitol and the widely used `OH^• trap'' salicylate. However, D-NAME can scavenge OH^• at rates equal to L-NAME. Both L- and D-arginine were also good OH^• scavengers, comparable in effectiveness to mannitol.
3. Neither L-NAME, D-NAME, L-arginine nor D-arginine was able to inhibit ONOO⁻-dependent nitration of tyrosine, suggesting that they are unlikely to be scavengers of ONOO⁻-derived nitrating species.
4. Neither L-NAME, D-NAME, L-arginine nor D-arginine was able to inhibit the inactivation of α₁-antiproteinase by ONOO⁻, suggesting that they cannot prevent direct oxidations by peroxynitrite.
5. We conclude that L-NAME has sufficient activity as an OH^• scavenger to confound certain pharmacological experiments. However, this explanation of its biological effects can be ruled out if control experiments show that D-NAME has no effect and that L-arginine (also a free radical scavenger) antagonizes the action of L-NAME.

     

Ramipril prevents the detrimental sequels of chronic NO synthase inhibition in rats: hypertension,cardiac hypertrophy and renal insufficiency

Inhibition of the angiotensin converting enzyme (ACE) with ramipril was studied in male Wistar rats during long-term inhibition of nitric oxide (NO) synthase by N^G-nitro-l-arginine methyl ester (l-NAME). Chronic treatment with l-NAME in a dose of 25 mg/kg per day over 6 weeks caused myocardial hypertrophy and a significant increase in systolic blood pressure (245 ± 16 mmHg) as compared to controls (155+4 mmHg). Animals receiving simultaneously l-NAME and ramipril were protected against blood pressure increase and partially against myocardial hypertrophy. L-NAME caused a significant reduction in glomerular filtration rate (GFR: 2.56+0.73 ml·kg^–1·min^–1) and renal plasma flow (RPF: 6.93±1.70ml·kg^–1·min^–1) as compared to control (GFR: 7.29±0.69, RPF: 21.36±2.33ml·kg^–1·min^–1). Addition of ramipril prevented l-NAME-induced reduction in GFR and renal plasma flow. l-NAME produced an elevation in urinary protein excretion and serum creatinine and a decrease in potassium excretion which was antagonised by ramipril. L-NAME-induced increase in plasma renin activity (PRA) was further elevated with ramipril treatment. Isolated hearts from rats treated with l-NAME showed increased post-ischaemic reperfusion injuries. Compared to controls duration of ventricular fibrillation was increased and coronary flow reduced. During ischaemia the cytosolic enzymes lactate dehydrogenase and creatine kinase, as well as lactate in the venous effluent were increased. Myocardial tissue values of glycogen, ATP, and creatine phosphate were decreased, whereas lactate was increased. Coadministration of ramipril reversed these effects. l-NAME treatment reduced the cyclic GMP content in urine and renal arteries, and was not changed by additional ramipril-treatment. In the kidney hyalinosis of arterioles and of glomerular capillaries, as well as mesangial expansion and tubular atrophies seen after long-term inhibition of NO synthase were reduced by coadministration of ramipril. In conclusion, long-term ACE inhibition by ramipril prevented l-NAME-induced hypertension and cardiac hypertrophy, and attenuated functional and morphological changes in the kidneys. In addition, cardiac-dynamic and -metabolic deterioration induced by L-NAME was normalised by co-treatment with ramipril. Correspondence to: Max Hropot at the above address     

Fetal and offspring arrhythmia following exposure to nicotine during pregnancy

Although recent studies have demonstrated prenatal nicotine can increase cardiovascular risk in the offspring, it is unknown whether exposure to nicotine during pregnancy also may be a risk for development of arrhythmia in the offspring. In addition, in previous studies of fetal arrhythmia affected by smoking, only two patterns, bradycardia and tachycardia, were observed. The present study examined acute effects of maternal nicotine on the fetal arrhythmia in utero, and chronic influence on offspring arrhythmia at adult stage following prenatal exposure to nicotine. Nicotine was administered to pregnant ewes and rats. In the fetal sheep, intravenous nicotine not only induced changes of fetal heart rate, but also caused cardiac cycle irregularity, single and multiple dropped cardiac cycles. Although maternal nicotine had no influence on fetal blood pH, lactic acid, hemocrit, Na⁺, K⁺ levels and plasma osmolality, fetal blood PO₂ levels were significantly decreased following maternal nicotine in ewes. In offspring rats at 4–5 months after birth, prenatal exposure to nicotine significantly increased heart rate and premature ventricular contraction in restraint stress. In addition, arrhythmias induced by injection of nicotine were higher in the offspring prenatal exposure to nicotine in utero. The results provide new evidence that exposure to nicotine in pregnancy can cause fetal arrhythmia in various patterns besides tachycardia and bradycardia, the possible mechanisms for nicotine‐induced fetal arrhythmia included in utero hypoxia. Importantly, following exposure to nicotine significantly increased risk of arrhythmia in the adult offspring. The finding offers new insight for development of cardiac rhythm problems in fetal origins. Copyright © 2009 John Wiley & Sons, Ltd.