Nitric oxide-compromised hypertension: facts and enigmas

NO concentration in the femoral artery and femoral vein of anesthetized dogs was found to be 154.2+/-5.6 nM and 90.0+/-12 nM, respectively. Inhibition of NO synthase (NOS) slightly decreased the basal NO concentration in femoral artery from 154.2+/-5.6 to 137.2+/-3.3 nM. Acetylcholine-induced increase in NO concentration was slightly but still significantly attenuated, suggesting that very probably L-NAME did not inhibit all sources of nitric oxide (NO). Local NOS inhibition in the posterior hypothalamus dose-dependently increased systemic blood pressure (BP) in rats. Short-term general NOS inhibition in anesthetized dogs increased diastolic BP but not systolic BP. The heart rate after one-hour down-fluctuation returned to initial values. Proteosynthesis in the myocardium and both branches of the left coronary artery increased, but this was not supported by polyamines, since the activity of ornithine decarboxylase declined. Long-term general NOS inhibition elicited a sustained BP increase, a decrease in heart rate, cardiac hypertrophy and an increase in wall thickness of the coronary and carotid artery. The results indicate that NO deficiency itself plays a role in proteosynthesis and cardiac hypertrophy, in spite of relatively small increase in diastolic blood pressure and no change in systolic blood pressure, at least after an acute L-NAME administration. The hypotension response to acetylcholine and bradykinin studied in anesthetized NO-compromised rats, was unexpectedly enhanced. The elucidation of this paradoxical phenomenon will require further experiments.     

Long-term effect of molsidomine and pentaerythrityl tetranitrate on cardiovascular system of spontaneously hypertensive rats

We studied the effects of long-term administration of molsidomine and pentaerythrityl tetranitrate (PETN) on the cardiovascular system of spontaneously hypertensive rats (SHR). One control and three experimental groups of 10-week-old animals were used: 1) control Wistar rats, 2) SHR, 3) SHR treated with molsidomine in tap water (100 mg/kg/day, by gavage), and 4) SHR treated with PETN in tap water (200 mg/kg/day, by gavage). After six weeks, the content of cGMP in platelets and NO synthase (NOS) activity in aortas were evaluated in the experimental groups. For morphological evaluation the rats were perfused at 120 mm Hg with a glutaraldehyde fixative and the arteries were processed for electron microscopy. Blood pressure and heart weight/body weight ratio (HW/BW) were increased in all experimental groups with respect to the controls. HW/BW was lower in the molsidomine group in comparison to both SHR and PETN-treated group. The platelet content of cGMP was increased and the activity of NOS in the aortas was decreased in the molsidomine and PETN-treated groups. Wall thickness and cross-sectional area of thoracic aorta, carotid artery and coronary artery were increased similarly in all experimental groups compared to the controls, but there were no differences among the experimental groups. We summarize that long-term administration of exogenous NO donors did not improve pathological changes of the cardiovascular system in SHR.     

Acetylcholine and bradykinin induce paradoxically amplified hypotensive response in hypertensive NO-deficient rats

The hypotensive response to acetylcholine and bradykinin was studied in rats with NO synthase activity inhibited for a short period of 2 h or a long period of 6 weeks. N(G)-nitro-L-arginine-methyl ester (L-NAME) was used as NO synthase inhibitor (given in a dose of 50 mg/kg either into the jugular vein, or daily in drinking water). Blood pressure was measured in the right carotid artery by a Statham pressure transducer in acute experiments, and on the tail artery by the plethysmographic method weekly in chronic experiments. During both the short- and long-lasting NO synthase inhibition blood pressure rose significantly. The heart rate decreased significantly in rats treated with L-NAME for 6 weeks. Surprisingly, the hypotensive responses to acetylcholine and bradykinin were present in both experimental groups. Paradoxically, the hypotensive responses to all three doses of acetylcholine were remarkably enhanced in rats with NO synthase inhibition lasting 6 weeks, in comparison to both age-matched controls and to rats subjected to short-lasting NO synthase inhibition. The blockade of muscarinic receptors by atropine abolished the hypotensive response to acetylcholine but not to bradykinin. The hypothetical mechanisms underlying this unexpected paradoxical phenomenon of cardiovascular control are discussed.     

The impact of L-NAME and L-arginine chronic toxicity induced lesions on ascites--pulmonary hypertension syndrome development in broiler chickens

The impact of L-arginine (LA), a precursor for synthesis of nitric oxide (NO), and N-omega-nitro-L-arginine methyl ester (L-NAME, LN), a non-selective inhibitor of the enzyme producing nitric oxide (nitric oxide synthase; NOS) chronic toxicity induced lesions on Ascites - Pulmonary hypertension syndrome (PHS) development was investigated in 140 one-day-old male broiler chickens (ROSS) during the first 5 weeks of life. Every second day the animals were treated intraperitoneally (ip) with L-NAME (10 mg/kg of body weight; BW), L-arginine (100 mg/kg BW), L-arginine and L-NAME in combination (100 mg/kg BW and 10 mg/kg BW respectively), and with physiological saline (0.90% w/v of NaCl; 0.5 mL/kg BW). Seven birds from each group were euthanized every week. The histopathological examination of the heart, the liver, the lungs, the blood vessels and the lymphoid organs, was performed. Also the organ index values were determined. At the end of the experiment the pre-ascitic condition or ascites - PHS was confirmed in five dead animals in the L-NAME-treated group. In the same group the edema was the most prominent histopathological change confirmed in the heart and in the lungs of the sacrificed chickens. In L-arginine-treated group the congestion and the haemorrhages were the striking changes in the same organs with the highest degree in the last two weeks of trial. While the focal disruption of myocardiofibriole and hepatocytes were predominant lesions in L-NAME-treated chickens (5th and 4th weeks, respectively), in L-NAME/L-arginine-treated group only the mild focal myocardial degeneration was seen. According to the most of the results of present investigation, it was concluded that the consecutive treatment with L-NAME provoked ascites - PHS, while L-arginine has protective effect in this animal model of disease.     

Modulation of ornithine decarboxylase activity and ornithine decarboxylase-antizyme complex in rat heart by hormone and putrescine treatment

Ornithine decarboxylase was present in a cryptic, complexed form in an amount approximately equivalent to that of free ornithine decarboxylase activity in adult rat heart. Addition of isoproterenol (10 mg/kg) caused a notable rise in ornithine decarboxylase activity and a simultaneous decrease in the amount of the complexed enzyme. During the period of ornithine decarboxylase decay, when cardiac putrescine content had reached high values, the level of the complex increased above that of the control. Administration of putrescine (1.5 mmol/kg, twice) or dexamethasone (4 mg/kg) produced a decrease of heart ornithine decarboxylase activity, while it did not remarkably affect the level of complexed ornithine decarboxylase, therefore raising significantly the ratio of bound to total ornithine decarboxylase. Putrescine also elicited the appearance of free antizyme, concomitantly with the disappearance of free ornithine decarboxylase activity after 3-4 h of treatment. These results indicate that a significant amount of ornithine decarboxylase occurs in an inactive form in the heart under physiological conditions and that its absolute and relative levels may vary following stimuli which affect heart ornithine decarboxylase activity.     

Early changes of protein synthesis in myocardium and coronary arteries induced by NO synthase inhibition.

The question was addressed whether short-term (4 hour) NO deficiency, inducing an increase in blood pressure in anaesthetized dogs, does influence proteosynthesis in the myocardium and coronary arteries. A potentially positive answer was to be followed by the study of the supporting role of ornithine decarboxylase for the polyamines pathway. N(G)-nitro-L-arginine-methyl ester (L-NAME) (50 mg/kg per hour) was administered i.v. to inhibit NO synthase. After the first L-NAME dose diastolic blood pressure increased from 131.8+/-2.0 to 149.4+/-3.9 mm Hg (p<0.001) and was maintained at about this level till the end of the experiment. Systolic blood pressure only increased after the first dose (from 150.8+/-1.1 to 175.0+/-5.8 mm Hg, p<0.01), returning thereafter to the control level. Similarly, the heart rate declined only after the first dose (from 190.4+/-5.3 to 147.6+/-4.5 beats/min, p<0.01). Total RNA concentrations increased in the left cardiac ventricle (LV), the left anterior descending coronary artery (LADCA) and left circumflex coronary artery (LCCA) by 15.9+/-0.7, 29.7+/-1.3 and 17.6+/-1.0%, p<0.05, respectively. The same applied to [14C]leucine incorporation (by 86.5+/-5.0, 33.5+/-2.6, 29.3+/-4.1%, p<0.05, respectively). The above parameters indicated an increase of proteosynthesis in the LV myocardium and both coronary arteries LADCA and LCCA after short-term NO deficiency. Surprisingly, the ornithine decarboxylase activity in the LV myocardium decreased significantly by 40.2+/-1.6% (p<0.01) but the changes were not significant in the coronary arteries. This unexpected finding makes the role of polyamines in increasing proteosynthesis during a pressure overload due to NO deficiency questionable.     

Role of nitric oxide in lower esophageal sphincter relaxation to swallowing.

Studies were performed in the opossum to define the role of the L-arginine-nitric oxide (NO) pathway in lower esophageal sphincter (LES) relaxation to swallowing and vagal stimulation in viv and intramural nerve stimulation in vitro. In vivo, L-NAME, a water soluble NO synthase (NOS) inhibitor, caused antagonism of LES relaxation due to reflex-induced swallowing. L-NAME (20 mg/kg i.v.) reduced the amplitude of swallow induced relaxation from 88% to 28%. LES relaxation due to electrical stimulation of peripheral end of decentralized vagus nerve was also antagonized. The effects of L-NAME were reversed by L-arginine, but not by D-arginine. L-NAME treatment did not antagonize LES relaxation to intravenous administration of isoproterenol. In vitro, NO and sodium nitroprusside (SNP) caused a decrease in the sphincter tone. The relaxing effect caused by NO and SNP was not antagonized by tetrodotoxin or omega-conotoxin. Inhibitors of NO synthase, L-NMMA and L-NNA, caused slight increase in the spontaneous resting LES tone and concentration-dependent antagonism of electrical field stimulation (EFS) induced LES relaxation. L-NNA (10(-4)M) abolished EFS induced LES relaxation at low frequencies (less than 5 Hz) and antagonized the relaxation to a value 20% of the control at 20 Hz. The antagonistic action of L-NMMA and L-NNA was unaffected by D-arginine but was reversed by L-arginine. The inhibitory effect of NO, SNP, or two other putative inhibitory neurotransmitters (VIP and CGRP) on the LES was not antagonized by L-NNA. These studies show that inhibitors of NO synthase selectively antagonize LES relaxation to all three modes of intramural inhibitory nerve stimulation including physiological swallowing. These studies suggest that the L-arginine-nitric oxide pathway is involved in physiological relaxation of the LES.     

Red wine polyphenols induce vasorelaxation by increased nitric oxide bioactivity

The aim of the present study was to investigate the mechanism of vasorelaxant responses induced by red wine polyphenolic compounds (Provinol). Rings of rat femoral artery with or without functional endothelium were set up in a myograph for isometric recording and precontracted with phenylephrine (10(-5) M). Provinol in cumulative doses (10(-9) to 10(-3) mg/ml) elicited endothelium- and dose-dependent relaxation of the artery with maximal relaxation of 56 per cent at the concentration of 10(-5) mg/ml. The relaxant responses to Provinol correlated well with the increase of NO synthase activity in the vascular tissue after administration of cumulative doses of Provinol (10(-9) to 10(-3) mg/ml). N(G)-nitro-L-arginine methylester (L-NAME, 3x10(-4) M) significantly attenuated the endothelium-dependent relaxation produced by Provinol. Administration of L-arginine (3x10(-5) M) restored the relaxation inhibited by L-NAME. The relaxant responses of Provinol were abolished in the presence of Ca(2+)-entry blocker, verapamil (10(-6) M). Administration of hydrogen peroxide (H(2)O(2)) abolished acetylcholine (10(-5) M)-induced relaxation of the rat femoral artery, while administration of Provinol (10(2) mg/ml) together with H(2)O(2) helped to maintain the acetylcholine-induced relaxation. Provinol only partially affected the concentration-response curve for the NO donor sodium nitroprusside-induced relaxation in rings without endothelium. In conclusion, Provinol elicited endothelium-dependent relaxation of rat femoral artery by the Ca(2+)-induced increase of NO synthase activity and by protecting NO from degradation.     

Ultrastructural and electrophysiological alterations during the development of catecholamine-induced cardiac hypertrophy and failure

Cardiac hypertrophy and failure were induced in male Wistar rats by daily administration of 5 mg/kg isoproterenol for three weeks. Age-matched animals were used as normal control. To estimate the degree of hypertrophy, the wet heart weight (HW) to body weight (BW) ratio (HW/BW) was used as an index of the myocardial enlargement. By the 7th day of the treatment, the HW/BW ratio was increased to 4.24, as compared with the control value of 3.11. In this early stage of cardiomyopathy, the structure was characterized with small necrotic foci, enlarged myofilaments and swollen mitochondria. The electrical activity showed broadened action potentials with an elevated plateau phase, and increased membrane resistance and time constant. The amplitude of the twitch contractions was elevated. Continuing the treatment of the animals with catecholamine caused a decompensated heart failure by the 21st day. In this late stage, many and large necrotic foci could be observed in the myocardium. The mitochondria were fragmented, and the resistance of the sarcolemma decreased, and the electrical and contractile activity suppressed. The results indicate that an electrically and structurally compensated cardiac hypertrophy model can be produced by a short-term treatment of the animals with isoproterenol, while a long-term treatment causes a decompensated heart failure.     

Long-term administration of D-NAME induces hemodynamic and structural changes in the cardiovascular system

N(G)-nitro-D-arginine-methyl ester (D-NAME) is considered to be an inactive enantiomer of L-NAME and is generally used as the negative control for NO synthase inhibition with L-NAME. With the aim to compare the effects of 4-week L-NAME and D-NAME treatments on hemodynamic and cardiovascular structural parameters, four groups of male Wistar rats were investigated: the controls and groups administered 40 and 20 mg/kg/day of L-NAME and 40 mg/kg/day of D-NAME. At the end of the experiment, myocardial NO synthase activity decreased by 42, 24 and 25%; aortic NO synthase activity decreased by 35, 15 and 13% vs. controls in the L-NAME 40, L-NAME 20 and D-NAME 40 groups, respectively. The DNA concentrations in the myocardium and the aorta increased significantly after L-NAME and D-NAME treatments. The inhibition of NO synthase was accompanied by a significant elevation in systolic blood pressure in all three groups. The LVW/BW ratio increased by 27, 14 and 13% vs. controls in the L-NAME 40, L-NAME 20 and D-NAME 40 groups, respectively. The aortic wall mass, measured as the cross-sectional area, increased by 45, 17 and 25% vs. controls in the L-NAME 40, L-NAME 20 and D-NAME 40 groups, respectively. Myocardial fibrosis represented 0.94% in the controls, but 7.96, 4.70 and 5.25% in L-NAME 40, L-NAME 20 and D-NAME 40 groups, respectively. It is concluded that D-NAME, although less affective than L-NAME, inhibits NO synthase activity resulting in hemodynamic and structural changes in the cardiovascular system similar to the changes induced by half the dose of L-NAME. Thus, the consideration of D-NAME as an inactive enantiomer and its use as the negative control needs to be reevaluated.     

Gender-dependent response in blood pressure changes following the inhibition of nitric oxide synthase

Many studies employed L-NAME (N(G)-nitro-L-arginine methyl ester), an L-arginine antagonist and nitric oxide (NO) synthase (NOS) inhibitor, to produce hypertension experimentally in male animals. It is not known whether females respond similarly. We thus examined the effect of long-term oral administration of L-NAME on body weight (BW), blood pressure (BP), and heart rate (HR) of both female and male rats. We found that L-NAME induced significant increase in mean BP (MAP) in both genders, however, L-NAME-treated females (F*) exhibited a significantly higher elevation than males (M*) did. This difference persisted for 5 wks and then diminished. L-NAME was thus withdrawn and a rapid decrease of MAP was observed. MAP of F* decreased less and thus remained higher than M* for 5 wks. MAP of control rats (F and M) remained unchanged during the period. Systolic BP (SBP) altered in a similar pattern. We also found that HR decreased immediately after L-NAME administration and that HR of F* was significantly less reduced. These findings indicate that L-NAME induced a more pronounced response in females than males, consistent with the view that females are more dependent on NOS activity for their regulation of BP.     

Antihypertensive effects of onion on NO synthase inhibitor-induced hypertensive rats and spontaneously hypertensive rats

This study was designed to show the effects of onion on blood pressure in N(G)-nitro-L-arginine methyl ester (L-NAME) induced-hypertensive rats and stroke prone spontaneously hypertensive rats (SHRSP) using dried onion at 5% in their diets. For the experiment with L-NAME induced-hypertensive rats, male 6-weeks-old Sprague-Dawley rats were given tap water containing L-NAME to deliver 50 mg/kg BW/day. In this experiment, we found distinct antihypertensive effects of onion on the L-NAME induced-hypertensive rats and the SHRSP. Dietary onion decreased the thiobarbituric acid reactive substances (TBARS) in plasma in these hypertensive rats. Also, onion increased the nitrate/nitrite (products of nitric oxide (NO)) excreted in urine and the NO synthase (NOS) activity in the kidneys in SHRSP. These results suggested that the increased NO caused by the greater NOS activity, and additionally by the increased saving of NO by the antioxidative activity of onion, was one of the cause of the antihypertensive effect of onion in SHRSP. In the L-NAME induced hypertensive rats, onion did not significantly block the inhibition of NOS activity by L-NAME, and decreased nitrate/nitrite excretion in urine was not restored. The mechanism of the antihypertensive effect of onion probably involves increased saving of NO by antioxidative activity of onion in L-NAME induced-hypertensive rats.     

Gender-specific genetic determinants of blood pressure and organ weight: pharmacogenetic approach

A total genome scan and pharmacogenetic study were designed to search for genetic determinants of blood pressure (BP) as well as heart and kidney weights. Genome scanning was carried out in 266 F(2) intercrosses from Prague hypertensive hypertriglyceridemic rats for phenotypes of organ weights, baseline BP, BP after blockade of the renin-angiotensin system (RAS) by losartan, of the sympathetic nervous system (SNS) by pentolinium, and of the nitric oxide (NO) synthase by N(G)-nitro-L-arginine methyl ester. Pharmacogenetic analysis showed that, in males, BP was controlled by two loci on chromosomes 1 and 5 (Chr1, Chr5) through the SNS, and these loci showed a positive contribution for relative kidney weight (KW/BW). On the other hand, baseline BP in females was controlled by two loci on Chr3 and Chr7. The effect of these loci was not mediated by the RAS, SNS or NO system. These loci did not show any effect for KW/BW. Negatively-linked loci for KW/BW and relative heart weight (HW/BW) were identified on Chr2 in both genders. Another negatively-linked locus for KW/BW, located on Chr8 in males, affected BP through the SNS. This locus on Chr8 overlapped with a previously-reported modifier locus for polycystic kidney disease (PKD). In conclusion, this pharmacogenetic study determined two loci for BP and relative organ mass implicating sympathetic overactivity. Concordance of the identified locus for KW/BW and BP through the SNS on Chr8 with the PKD locus revealed the importance of this region for renal complications in various diseases.     

Nitric oxide (NO) is involved in modulation of non-insulin mediated glucose transport in chicken skeletal muscles

The biosynthesis and release of nitric oxide (NO) from skeletal muscle plays a crucial role in transport and utilization of glucose. There are, however, no reports concerning the effects of NO on the transport of glucose in skeletal muscles of chickens characterized by hyperglycemia and insulin resistance. The present study was undertaken to investigate whether a NO donor or a nitric oxide synthase (NOS) inhibitor influences basal or insulin-mediated glucose uptake in vivo in skeletal muscles of chickens. Single administration of NOC12, a NO donor at 1125 microg/kg body mass (BW) to 14 days old chicks caused an increase in plasma NO concentration, while it did not affect plasma glucose concentration. In contrast, a single injection of NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) at 300 mg/kg BW reduced plasma NO concentration, while it did not effect plasma glucose concentration. Chicks were also treated with or without NO modifier and/or insulin to estimate glucose transport activity, which was estimated by the 2-deoxy-D-glucose (2DG) uptake method. NOC12 treatment significantly increased basal glucose uptake, with no insulin stimulation, in extensor digitrorum longus (EDL) muscle (P<0.01), while it caused no significant changes in insulin-stimulated glucose uptake in the skeletal muscles assayed. Injection of L-NAME at 300 mg/kg BW resulted in a significant decrease in the basal glucose uptake in gastrocnemius muscles (P<0.01). No significant changes in the insulin-stimulated glucose uptake by L-NAME were observed in any skeletal muscles studied. The results suggest that NO plays a lesser role in the modulation of glucose transport in chicken skeletal muscle compared to mammals and may be involved in non-insulin mediated glucose transport.     

Glyceryl trinitrate, a nitric oxide donor, suppresses renal oxidant damage caused by potassium bromate

Nitric oxide (NO) is a short-lived, readily diffusible intracellular messenger molecule associated with multiple organ-specific regulatory functions. Endogenous stimulation or exogenous administration of NO have been shown to inhibit production of reactive oxygen species (ROS) and expression of oxidant-mediated molecular or tissue injury. Potassium bromate (KBrO3) is one such potent renal oxidant that acts through generation of ROS-mediated lipid peroxidation, and causes increased ornithine decarboxylase activity, enhanced rate of DNA synthesis and depletion of the antioxidant armoury of the tissue. In this study, we elucidate the effect of exogenous NO administration, using the NO donor glyceryl trinitrate (GTN), on KBrO3-induced nephrotoxicity, oxidative stress and cell proliferation. KBrO3 administration at a dose of 125 mg/kg body weight results in significant (P < 0.001) depletion in renal glutathione (GSH) content, and glutathione reductase (GR) activity with a concomitant increase in microsomal lipid peroxidation, and blood urea nitrogen (BUN) and creatinine levels. Parallel to these changes, we found significant enhancement in ornithine decarboxylase (ODC) activity and rate of renal DNA synthesis. Subsequent administration of GTN resulted in dose-dependent amelioration of GSH content and GR activity with concomitant inhibition of lipid peroxidation, and BUN and creatinine levels. In addition, GTN administration to KBrO3-intoxicated rats resulted in significant dose-dependent down regulation of enhanced ODC activity and rate of [3H]-thymidine incorporation in renal DNA, providing support for the protective role of NO in attenuation of KBrO3-induced oxidative stress and cell proliferation. Enhancement of oxidative tissue injury and cell proliferation on administration of the NO inhibitor, L-NAME, further demonstrates the protective efficacy of endogenous NO. These data suggest that NO inhibits KBrO3-induced tissue injury, oxidative stress and proliferative response in the rat kidney.     

The time-dependent effect of Provinols on brain NO synthase activity in L-NAME-induced hypertension

Red wine polyphenols have been reported to possess beneficial properties for preventing cardiovascular diseases but their neuroprotective effects during chronic L-NAME treatment have not been elucidated. The aim of this study was to analyze a time course of Provinols effects on brain NO synthase activity and oxidative damage in L-NAME-induced hypertension. Male Wistar rats, 12 weeks old, were divided into six groups: control groups, groups treated with N(G)-nitro-L-arginine methyl ester (L-NAME, 40 mg/kg/day) for 4 or 7 weeks and groups receiving Provinols (40 mg/kg/day) plus L-NAME for 4 or 7 weeks. At the end of the treatment, marker of membrane oxidative damage - conjugated dienes (CD) in the brain and NO synthase activity in the cerebral cortex, cerebellum and brainstem were determined. L-NAME treatment for 4 or 7 weeks led to the increase in blood pressure, elevation of CD concentration and decrease of NO synthase activity in the brain parts investigated. Provinols partially prevented blood pressure rise and elevation of CD concentration. Comparing to the L-NAME treated group, Provinols increased NO synthase activity after 4 weeks of treatment. However, the prolonged Provinols treatment for 7 weeks had no effect on NO synthase activity decreased by L-NAME treatment. In conclusion, Provinols partially prevents L-NAME induced hypertension via the different mechanisms depending on the duration of treatment. Prevention of oxidative damage in the brain with modulating effect on NO synthase activity is suggested.     

Thyroxine-induced cardiac hypertrophy: influence of adrenergic nervous system versus renin-angiotensin system on myocyte remodeling

The present study assessed the possible involvement of the renin-angiotensin system (RAS) and the sympathetic nervous system (SNS) in thyroxine (T4)-induced cardiac hypertrophy. Hemodynamic parameters, heart weight (HW), ratio of HW to body weight (HW/BW), and myocyte width were evaluated in absence of thyroid hormone (hypothyroidism) and after T4 administration. Male Wistar rats were used. Some were subjected to thyroidectomies, whereas hyperthyroidism was induced in others via daily intraperitoneal injection of T4 (25 or 100 microg x 100 g BW(-1) x day(-1)) for 7 days. In some cases, T4 administration was combined with the angiotensin I-converting enzyme inhibitor enalapril (Ena), with the angiotensin type 1 (AT1) receptor blocker losartan (Los) or with the beta-adrenergic blocker propanolol (Prop). Hemodynamics and morphology were then evaluated. Systolic blood pressure (SBP) was not altered by administration of either T4 alone or T4 in combination with the specific inhibitors. However, SBP decreased significantly in hypothyroid rats. An increased heart rate was seen after administration of either T4 alone or T4 in combination with either Los or Ena. Although the higher dose of T4 significantly increased HW, HW/BW increased in both T4-treated groups. Ena and Prop inhibited the increase in HW or HW/BW in hyperthyroid rats. Morphologically, both T4 dose levels significantly increased myocyte width, an occurrence prevented by RAS or SNS blockers. There was a good correlation between changes in HW/BW and myocyte width. These results indicate that T4-induced cardiac hypertrophy is associated with both the SNS and the RAS.     

Chronic low-dose L-NAME treatment increases nitric oxide production and vasorelaxation in normotensive rats

N(G)-nitro-L-arginine methyl ester (L-NAME) is a non-specific nitric oxide (NO) synthase inhibitor, commonly used for the induction of NO-deficient hypertension. The aim of this study was to investigate the effect of chronic low-dose administration of L-NAME on NO production, vascular function and structure of the heart and selected arteries of rats. Adult male Wistar rats were treated with L-NAME in the dose of approximately 1.5 mg/kg/day in drinking water for 8 weeks. Basal blood pressure (BP) of rats (determined by tail-cuff) was 112+/-3 mm Hg. The low-dose administration of L-NAME significantly elevated BP measured on the third and sixth week of treatment vs. controls by approximately 9 % and 12 %, respectively. After this period, BP of L-NAME-treated rats returned to the control values. The relative left ventricular mass, heart fibrosis and collagen III/collagen I ratio were not affected by L-NAME. Similarly, there were no alterations in the cross-sectional area and wall thickness/diameter ratio of the aorta and the femoral artery of L-NAME-treated rats. NO synthase activity (determined by conversion of [(3)H]-L-arginine to [(3)H]-L-citrulline) was not altered in the hypothalamus of L-NAME-treated rats. Interestingly, chronic low-dose L-NAME treatment significantly elevated NO synthase activity in the left ventricle and aorta, increased endothelium-dependent acetylcholine-induced vasorelaxation and reduced serotonin-induced vasoconstriction of the femoral artery. The data suggest that chronic low-dose L-NAME treatment can increase NO production and vasorelaxation in normotensive rats without negative structural changes in the cardiovascular system.     

Nonpeptide endothelin receptor antagonists attenuate the pressor effect of diaspirin-crosslinked hemoglobin in rat.

Endothelin 1 (ET-1) is a potent vasoactive and mitogenic peptide that is thought to participate in the hemodynamic effects elicited by drugs that block the biosynthesis and release of endothelium-derived nitric oxide (NO), such as NO synthase inhibitors. Using the nonpeptide endothelin receptor antagonists bosentan and LU-135252, we tested the hypothesis that endothelins contribute to the pressor activity of diaspirin-crosslinked hemoglobin (DCLHb), a hemoglobin-based oxygen carrier, whose pressor activity in mammals is attributed primarily to a scavenging action towards NO. The NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME), ET-1, and noradrenaline (NA) were used as reference drugs. Bosentan markedly reduced the pressor effects elicited by DCLHb, L-NAME, and ET-1, but not those evoked by NA. LU-135252 attenuated the pressor effect elicited by DCLHb and ET-1, but not that produced by L-NAME or NA. The decreases in heart rate associated with the pressor effect of DCLHb and L-NAME were reduced by LU-135252, whereas only those elicited by DCLHb were attenuated by bosentan. In contrast with bosentan, LU-135252 caused a decrease in the baseline blood pressure and heart rate. These results suggest that endothelins may participate in the pressor activity of DCLHb. They suggest also that nonpeptide endothelin receptor antagonists such as bosentan or LU-135252 may be useful to counteract endothelin-mediated undesirable hemodynamic effects of drugs that inhibit the activity of the NO system.