Stereology and immunohistochemistry of the myocardium in experimental hypertension: long-term and low-dosage administration of inhibitor of the nitric oxide synthesis

Genistein prevents isoproterenol-induced cardiac hypertrophy in rats

Genistein, an isoflavone and a rich constituent of soy, possesses important regulatory effects on nitric oxide (NO) synthesis and oxidative stress. Transient and low release of NO by endothelial nitric oxide synthase (eNOS) has been shown to be beneficial, while high and sustained release by inducible nitric oxide synthase (iNOS) may be detrimental in pathological cardiac hypertrophy. The present study was designed to evaluate whether genistein could prevent isoproterenol-induced cardiac hypertrophy in male Wistar rats (150–200 g, 10–12 weeks old) rats. Isoproterenol (5 mg·(kg body weight)–1) was injected subcutaneously once daily for 14 days to induced cardiac hypertrophy. Genistein (0.1 and 0.2 mg·kg–1, subcutaneous injection once daily) was administered along with isoproterenol. Heart tissue was studied for myocyte size and fibrosis. Myocardial thiobarbituric acid reactive substances (TBARS), glutathione (GSH), superoxide dismutase (SOD), catalase levels, and 1-OH proline (collagen content) were also estimated. Genistein significantly prevented any isoproterenol-induced increase in heart weight to body weight ratio, left ventricular mass (echocardiographic), myocardial 1-OH proline, fibrosis, myocyte size and myocardial oxidative stress. These beneficial effects of genistein were blocked by a nonselective NOS inhibitor (L-NAME), but not by a selective iNOS inhibitor (aminoguanidine). Thus, the present study suggests that the salutary effects of genistein on isoproterenol-induced cardiac hypertrophy may be mediated through inhibition of iNOS and potentiation of eNOS activities.

Lack of Endothelial Nitric Oxide Synthase–Derived Nitric Oxide Formation Favors Hypertrophy in Adult Ventricular Cardiomyocytes

Reduced activity and expression of endothelial NO synthase (eNOS) is observed in cardiomyocytes from pressure-overloaded hearts with heart failure. The present study was aimed to investigate whether reduced eNOS-derived NO production contributes to the hypertrophic growth and phenotype of these cardiomyocytes. Cultured ventricular cardiomyocytes from adult rats were exposed to Nω-nitro- l -arginine ( l -NNA) to inhibit global NO formation, and cultured cardiomyocytes derived from eNOS-deficient mice were used as a model of genetic knockout of eNOS. Cell growth, formation of oxygen-derived radicals (reactive oxygen species [ROS]), activation of p38 mitogen-activated protein (MAP) kinase phosphorylation, and cytokine expression in cardiomyocytes were investigated. l -NNA caused a concentration-dependent acceleration of the rate of protein synthesis and an increase in cell size. This effect was sensitive to p38 MAP kinase inhibition or antioxidants. l -NNA induced a rapid increase in ROS formation, subsequent activation of p38 MAP kinase, and p38 MAP kinase–dependent increases in the expression of transforming growth factor-β and tumor necrosis factor-α. Similar changes (increased ROS formation, p38 MAP kinase phosphorylation, and cytokine induction) were also observed in cardiomyocytes derived from eNOS+/+ mice when exposed to l -NNA. Cardiomyocytes from eNOS−/− mice displayed higher p38 MAP kinase phosphorylation and cytokine expression under basal conditions, but neither these 2 parameters nor ROS formation were increased in the presence of l -NNA. In conclusion, our data support the hypothesis that reduced eNOS activity in cardiomyocytes contributes to the onset of myocardial hypertrophy and increased cytokine expression, which are involved in the transition to heart failure.

Exercise training attenuates cardiovascular adverse remodeling in adult ovariectomized spontaneously hypertensive rats

OBJECTIVE

To study the combined effects of ovariectomy and regular exercise training on hypertension and on cardiac and aortic remodeling in spontaneously hypertensive rats (SHR).

DESIGN

Three-month-old female spontaneously hypertensive rats (SHR) were ovariectomized (ovx) or were left intact (int) and divided in four groups (n = 7): sedentary (sed-ovx), exercise-trained (ex-ovx), sedentary intact (sed-int), and exercise-trained intact (ex-int). The exercise protocol was performed on a motor treadmill for 13 weeks. Blood pressure (BP), left ventricular myocardium and aortic wall were studied by light microscopy and stereology.

RESULTS

Exercise-trained SHR showed a BP reduction of more than 15% compared with the matched sedentary SHR (sed-int: 210 +/- 5 mm Hg, sed-ovx: 225 +/- 4 mm Hg, ex-int: 178 +/- 2 mm Hg, ex-ovx: 180 +/- 3 mm Hg, P < 0.001). Ovariectomy caused adverse cardiac and aortic wall remodeling, including cardiomyocyte hypertrophy, myocardial interstitial reparative fibrosis and vascularization impairment with loss of cardiomyocytes, and aortic tunica media hypertrophy. Exercise training showed beneficial effects, mainly reduced BP, decreased cardiac hypertrophy due to hypertension, and increased myocardial vascularization. Ovariectomy accelerated cardiomyocyte loss in SHR while exercise training offset this process. Exercise training was the main factor influencing the improvement of intramyocardial arteries length density and significantly reduced the aortic wall thickness and increased the density of smooth muscle cell nuclei per tunica media unit area.

CONCLUSIONS

In ovariectomized SHR, exercise training exerts beneficial effects diminishing adverse cardiac and aortic wall remodeling, mainly by reducing interstitial myocardial fibrosis, improving myocardial vascularization, and sustaining the number of cardiomyocytes.

Dose-dependent autonomic dysfunction in chronic L-NAME-hypertensive diabetic rats

This study investigated the effects of varying doses of L-NAME on arterial pressure (AP), baroreflex control, and heart rate (HR)/AP variability in the STZ-diabetic rat. Fifty-two male Wistar rats were injected with 50 mg/kg IV STZ (diabetes, D, n = 24) or citrate (controls, C, n = 28) 30 days before recordings. After 16 days, they received 14 days of oral L-NAME, 10 (H10) or 30 (H30) mg/kg, or water. Catheters were implanted into the femoral artery and vein (PE-10) for measurements in conscious rats; recorded data were analyzed on a beat-to-beat basis. Mean AP was higher in CH30 versus C and in DH10 and DH30 versus D rats. Reflex tachycardia was blunted in CH30 and DH30 rats (b = -1.81, -1.41, -0.48 in C, CH10, and CH30, respectively, P < 0.05 and b = -1.45, -1.19, -0.28 in D, DH10, and DH30, respectively, P < 0.05). Although HR and AP variability were reduced in CH30 and DH30 rats versus C and D rats, the DH30 rat had more accentuated dysfunction. All doses of L-NAME produced similar AP responses in experimental versus control groups, independent of the disease state (diabetes). Thus, autonomic dysfunction is more related to the L-NAME dose used and to the association of diabetes and hypertension than to AP values.

Cardiopulmonary effects of chronic administration of the NO synthase inhibitor L-NAME in the chick embryo

BACKGROUND

Experimental observations in mammalian models suggest that endothelial nitric oxide (NO) synthase (NOS) content and activity are decreased in persistent pulmonary hypertension of the newborn.

OBJECTIVES

To test the hypothesis that disruption of NO signaling in the developing chick embryo lung may contribute to pulmonary hypertension.

METHODS

We analyzed pulmonary arterial reactivity and structure and heart morphology of 19-day chick embryos (incubation time 21 days) that received a daily injection of the NOS inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME, 20 mug per gram egg) or vehicle from day 12 until day 18.

RESULTS

Exposure to L-NAME did not affect embryonic survival or body mass of the embryos. The contractile responses to KCl, endothelin-1, the thromboxane A2 mimetic U46619, noradrenaline, and electrical-field stimulation were not affected by exposure to L-NAME. In contrast, in ovo L-NAME exposure reduced the sensitivity of pulmonary arteries to acetylcholine (pD2: 6.53 +/- 0.14 vs. 6.96 +/- 0.13; p < 0.05) and this effect was reversed by the NOS substrate L-arginine. Relaxations induced by sodium nitroprusside or forskolin were not altered by chronic L-NAME. Pulmonary vessel density was not different, but the percentage medial wall area of small pulmonary arteries (external diameter 10-50 microm) was slightly but significantly increased in the embryos exposed to L-NAME. In addition, hearts of L-NAME-exposed embryos showed an increase in right and left ventricular wall area.

CONCLUSIONS

Chronic inhibition of NOS produced, in the chick embryo, impairment of endothelium-dependent relaxation, structural remodeling of the pulmonary vascular bed and biventricular cardiac enlargement.

L-arginine fails to protect against myocardial remodelling in L-NAME-induced hypertension

BACKGROUND

We investigated whether the substrate for nitric oxide synthesis L-arginine is able to modify hypertension and left ventricular hypertrophy development induced by chronic blockade of nitric oxide synthase activity by NG-nitro-L-arginine-methyl ester (L-NAME).

MATERIAL AND METHODS

Four groups of rats were investigated: control, L-arginine 1.5 g kg-1, L-NAME 40 mg kg-1, and L-NAME +L-arginine in corresponding doses. Systolic blood pressure was measured by non-invasive tail-cuff plethysmography each week. After 4 weeks, the animals were sacrificed and hydroxyproline and coenzyme Q9 and Q10 concentrations in the left ventricle, and nitric oxide synthase activity in the left ventricle, kidney and brain were investigated.

RESULTS

In the L-NAME group, nitric oxide synthase activity was decreased in the left ventricle, kidney and brain, and hypertension, left ventricular hypertrophy and fibrosis developed. Heart remodelling was associated with the decrease of coenzyme Q9 and Q10 concentrations in the left ventricle. Simultaneous treatment with L-NAME and L-arginine prevented nitric oxide synthase activity diminution in the left ventricle but not in the kidney and brain, and completely failed to prevent hypertension, left ventricular hypertrophy and fibrosis. Nevertheless, l-arginine prevented the diminution of coenzyme Q9 and Q10 concentrations in the left ventricle.

CONCLUSIONS

We conclude that L-arginine failed to prevent hypertension, left ventricular hypertrophy and fibrosis development despite restoration of nitric oxide synthase activity in the left ventricle. However, L-arginine prevented the diminution of coenzyme Q levels in the left ventricle.

Offspring myocardium alteration from dams submitted to nitric oxide synthesis inhibition during pregnancy

BACKGROUND

Nitric oxide synthesis (NOS) inhibition during pregnancy alters offspring cardiac structure.

METHODS

Thirty female Wistar rats were assigned to two groups: control (15 rats) and LN (15 rats). LN rats received N(omega)-nitro-L-arginine methyl ester (L-NAME) during 5 weeks (2 weeks before matching and the weeks of pregnancy). Offspring were separated and sacrificed in three age groups (n=5): 2, 15 and 30 postnatal days. Left ventricular myocardium was analyzed with light microscopy and stereology.

RESULTS

BP increased significantly in LN matrices. No significant difference in neonate C-R length, body mass (BM) nor heart mass (HM) occurred in control and LN groups with 2 days of life. HM was greater in LN group than in control group from 15 days of life; BM was greater in LN group than in control group only with 30 days of life. HM/BM ratio was greater in LN neonates than in control neonates in all age groups. Vasculature total length (L[VE]) increased from days 2 to 15 and from days 15 to 30 and total number of cardiomyocyte nuclei profiles (N[CM]) also increased from days 2 to 30 in both LN and control neonates.

CONCLUSION

The offspring main cardiac structural alteration due to prenatal NOS inhibition is compatible with neonatal cardiac hypertrophy with intramyocardial vasculature enhancement. Furthermore, the prenatal NOS inhibition apparently stimulates the cardiomyocyte proliferation that can be observed until the end of lactation, which is when the number of cardiomyocytes nuclei profiles seems to become stable.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Beneficial effect of enalapril in spontaneously hypertensive rats cardiac remodeling with nitric oxide synthesis blockade

AIMS

To study the efficiency of an angiotensin converting enzyme inhibitor on the blood pressure (BP) and the myocardium remodeling when spontaneously hypertensive rats (SHRs) are submitted to nitric oxide synthesis (NOs) blockade (with L-NAME) and simultaneously treated.

METHODS

Young adult male SHRs were separated in four groups (n = 5) and treated for 20 days: Control, L-NAME, L-NAME+Enalapril, and Enalapril. The alterations of the BP, heart mass/body mass ratio and stereological parameters for myocytes, connective tissue and intramyocardial vessels were studied among the groups.

RESULTS

The SHRs with NOs blockade showed a great modification of the myocardium with extensive areas of reparative and interstitial fibrosis and accentuated hypertrophy of the cardiac myocytes (cross sectional area 60% higher in animals taking L-NAME than in Control SHRs). Comparing the SHRs with NO deficiency (L-NAME group), the Control SHRs and the Enalapril treated SHRs significant differences were found in the BP and in all stereological parameters. The NO deficiency caused an important BP increment in SHRs that was partially attenuated by Enalapril. This Enalapril effect was more pronounced in Control SHRs. A significant increment of the intramyocardial vessels was observed in NO deficient SHRs and Control SHRs treated with Enalapril demonstrated by the stereology (greater microvascular densities in treated SHRs).

CONCLUSION

Enalapril administration showed a beneficial effect on vascular remodeling and myocardial hypertrophy in SHRs. In SHRs with NO blockade, however, the beneficial effect of Enalapril occurred only in vascular remodeling.

Wine polyphenols improve cardiovascular remodeling and vascular function in NO-deficient hypertension

The effects of the red wine polyphenolic compounds (Provinol) on hypertension, left ventricular hypertrophy, myocardial fibrosis, and vascular remodeling were investigated after chronic inhibition of nitric oxide (NO) synthase by administration of N(G)-nitro-L-arginine methyl ester (L-NAME) to rats. Rats were divided into four groups: a control group, a group treated for 4 wk with L-NAME (40 mg x kg(-1) x day(-1)), and two groups treated with L-NAME followed by 3 wk of either spontaneous recovery or recovery with Provinol treatment (40 mg x kg(-1) x day(-1)). Administration of Provinol produced a greater readiness of the decrease in blood pressure than that in the spontaneous recovery group. Provinol significantly depressed myocardial fibrosis and expedited the decrease in aortic cross-sectional area, the increase in endothelium-dependent relaxation, and the decrease in contraction of the aorta. These effects of Provinol were associated with a greater increase of NO synthase activity in the left ventricle and the aorta. The present study provides evidence that Provinol accelerates the regression of blood pressure and improves structural and functional cardiovascular changes produced by chronic inhibition of NO synthesis.

Attenuation of hypertension, cardiomyocyte hypertrophy, and myocardial fibrosis by beta-adrenoceptor blockers in rats under long-term blockade of nitric oxide synthesis

The effects of propranolol and atenolol were investigated on arterial hypertension, cardiomyocyte hypertrophy, and ventricular ischaemic lesions induced by an 8-week treatment with the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 20 mg/rat per day) in Wistar rats. Propranolol and atenolol (30 mg/rat per day each) were given in the drinking water concomitantly to L-NAME. Treatment with L-NAME induced marked arterial hypertension and cardiomyocyte hypertrophy, both of which were significantly reduced by propranolol and atenolol. A marked repairing fibrosis was also observed in L-NAME-treated rats and this was significantly attenuated in animals receiving the beta-blockers. In L-NAME group, 33% mortality was observed, whereas all the animals from the other groups survived. Our study demonstrates that propranolol and atenolol reduce arterial hypertension, cardiomyocyte hypertrophy and myocardial fibrosis induced by L-NAME, suggesting that beta-blockers are of beneficial value in treatment of vascular and cardiac alterations caused by chronic nitric oxide deficiency.

The effect of enalapril and verapamil on the left ventricular hypertrophy and the left ventricular cardiomyocyte numerical density in rats submitted to nitric oxide inhibition

Forty male Wistar rats were separated into four groups of ten rats each (control and other three groups that have received nitric oxide (NO) synthesis inhibitor L-NAME) but the last two groups have concomitantly received antihypertensive drugs (Enalapril and Verapamil). After 40 days of experimentation, the heart and the ventricles were measured. The optical disector was used for the calculation of numerical density of the cardiomyocytes (Nv[c]). The left ventricular myocytes number (N[c]) was calculated as the product of Nv[c] and the left ventricular myocardium volume (LVMV) that was determined by using the Scherle's method. In the L-NAME group the blood pressure (BP) had a significant weekly increment. In the enalapril and the verapamil groups, BP increased in the first two weeks, but decreased in the following weeks. The LVMV increased in the L-NAME rats and decreased in the enalapril and verapamil animals. The Nv[c] and N[c] decreased in the L-NAME rats but the verapamil and enalapril treatments maintained the Nv[c] close to the control group. In conclusion, the left ventricular hypertrophy and the significant decrease of the left ventricular cardiomyocyte number caused by the NO synthesis inhibition are efficiently prevented with the use of enalapril and verapamil.

Effect of different high-fat diets on the myocardium stereology and blood pressure in rats

The effect of three high-fat diets containing 29% canola oil (CA), lard plus egg yolk (LE) or canola oil, lard and egg yolk (CA+LE) in male Wistar rats was investigated over a period of 6 months. We analyzed the myocardium, composed of cardiomyocytes and interstitium, which is made up of connective tissue and blood vessels. Volume density of cardiomyocyte (Vv[m]), volume density of blood vessels (Vv[v]), and volume density of connective tissue (Vv[ct]) were the stereological parameters determined. The rats of the LE group had a significantly higher heart mass/body mass ratio than those of the CA group. The blood pressure of the LE group was significantly higher than that of the other groups. In the CA group, the Vv[m] was significantly higher and the Vv[ct] was significantly lower than in the other groups. The myocardium of both the LE and CA+LE groups showed a significant reduction of Vv[m] and a compensatory increase of the Vv[ct]. These findings were less pronounced in the CA+LE group, in which the Vv[v] was found to be significantly higher than in the CA group. Comparing three high-fat diets, the data suggest that the diet canola oil had a major beneficial effect, preserving the myocardial structure and the blood pressure in rats.

Heart biometry and allometry in rats submitted to nitric oxide synthesis blockade and treatment with antihypertensive drugs

Fifty mature male rats were separated into groups of ten rats each (control, L-NAME, spironolactone, enalapril and verapamil). On the 41st day of experimentation, animals were anesthetized, weighed and sacrificed. The tail blood pressure (TBP) was 76% higher in L-NAME group than in the control group. Spironolactone, enalapril and verapamil were efficient in reducing TBP in those respective groups of rats (spironolactone was less efficient in reducing TBP). The heart mass/body mass ratio (HBR) increased 24% in L-NAME group and spironolactone group. No differences in HBR were found when control animals and animals treated with enalapril and verapamil were compared. Heart volume (HV) was greater in L-NAME group than other groups, but it was not different comparing the L-NAME and the spironolactone groups. The left ventricle was responsible for the changes in the HV. The relationship between the HV and the body mass (BM) was not significant in the groups L-NAME and spironolactone. However, this relationship was significant and allometric in control, enalapril and verapamil groups. In control group, HV had a positive allometric tendency against the BM, but in the enalapril and verapamil groups this tendency was allometrically negative. Cardiac hypertrophy in rats under inhibition of NO synthesis was prevented by treatment with enalapril and verapamil more efficiently than spironolactone.

Blood pressure, ventricular volume and number of cardiomyocyte nuclei in rats fed for 12 months on diets differing in fat composition

Blood pressure (BP), body mass (BM), ventricular volume (V[vent]) and the number of ventricular cardiomyocyte nuclei (N[vcn]) were analysed in rats fed different dietary fats. A total of 20 Wistar male rats were studied from 21 days old to 12 months of age and divided in the groups: soybean oil (S), canola oil (CA), lard and egg yolk (LE) and canola oil+lard and egg yolk (CA+LE). The diets had the same basal diet that included cornstarch, casein, maize, egg white and mineral and vitamin mixtures. At the moment of the sacrifice, the LE group had the greatest BP and V[vent] which was significantly higher than the other groups, and the S group had the greatest BM. The myocardial structure was apparently normal in the S and CA groups while it showed areas of diffuse interstitial fibrosis and hypertrophied cardiomyocytes in the LE group, and intramyocardial coronaries with thick tunica media and little interstitial fibrosis in CA+LE group. The N[vcn] was significantly higher in the CA group and it was lower in the LE group. These results suggest that the different dietary fats affect the myocardial structure, and the canola oil diet reduces the cardiomyocyte loss in the old rats.

Effect of antihypertensive drugs on the myocardial microvessels in rats with nitric oxide blockade

In the present study, myocardial microvessels were investigated by stereology in rats with nitric oxide blockade and concomitant antihypertensive treatment for 40 days. The following five groups (10 rats each) were studied: control; L-NAME; L-NAME + spironolactone; L-NAME + enalapril; L-NAME + verapamil. The blood pressure (BP) increased every week in the L-NAME group; after an initial increase BP decreased in the treated groups and was not different from the control group. Compared to control animals, the myocardium had hypertrophied myocytes and capillary rarefaction; the tunica media and the tunica intima of small arteries were thickened, and an increase in collagen fibrils in L-NAME treated animals was noted. The enalapril, verapamil and spironolactone groups showed uniform myocardium, quite similar to the control group. The volume density of vessels, in comparison with the L-NAME group, was greater in the spironolactone group (57%), in the enalapril group (76%) and in the verapamil group (81%). The length density of vessels was, respectively, 56%, 50%, and 76% greater in the spironolactone, enalapril and verapamil groups than in the L-NAME group. The surface density of the vessels of the L-NAME group was, respectively, 88%, 96%, and 113% lower than in the spironolactone, enalapril and verapamil groups. These results are compatible with the occurrence of angiogenesis in the verapamil rats.

Myofibroblast accumulation in healing rat myocardium due to long-term low-dosage nitric oxide synthesis inhibition

Inhibition of nitric oxide synthesis causes hypertension, myocardial damage and repair in rats. The myocardial healing process includes changes in extracellular matrix composition associated with the phenotypic modulation of fibroblasts. Early and later lesion areas showed a population of spindle-shaped cells expressing alpha-smooth muscle actin content. These cells apparently are associated with type III collagen and fibronectin accumulation in the ischemic lesion areas contributing to maintaining of the mechanical performance of the heart through out the healing process.

Development of cardiomyocyte hypotrophy in rats under prolonged treatment with a low dose of a nitric oxide synthesis inhibitor

Chronic administration of the nitric oxide (NO) synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) to rats causes hypertension and morphological abnormalities in the heart, consisting mainly of ventricular hypertrophy and foci of necrosis and fibrosis. Since these phenomena have usually been described with high (or moderate) doses of L-NAME, this study was undertaken to evaluate the effects of a low dose of L-NAME on arterial blood pressure, heart weight index, left ventricular weight index, amount of ventricular fibrosis, and cardiomyocyte size. Male Wistar rats received L-NAME (7.5 mg/kg per day) in the drinking water for 2, 4, and 6 months, whereas control animals received tap water alone. At this dose, L-NAME caused 90% inhibition (P<0.001) of brain NO synthase (NOS) activity. The chronic L-NAME treatment caused an approximately 15% reduction in body weight of the animals, and no death was observed. The tail-cuff pressure was markedly (P<0.01) elevated in L-NAME-treated rats. A significant (P<0.05) reduction in both heart weight index (13-20% decrease) and left ventricular weight index (20-34% decrease) at 2, 4, and 6 months of treatment was observed in L-NAME-treated rats. The cardiomyocyte size in subendocardial, subepicardial, and midmyocardial regions of the left ventricles was time-dependently reduced, irrespective of the region studied, as measured at 2 (11% decrease), 4 (28% decrease, P<0.05), and 6 (45% decrease, P<0.05) months of chronic L-NAME treatment. The amount of fibrous tissue was unaltered at 2 and 4 months, but a small (but significant) increase in the amount of fibrous tissue was detected at 6 months (7.1+/-0.2 %, P<0.05) compared to that of control animals (5.9+/-0.2%). Our results show that chronic treatment of rats with a low dose of L-NAME for prolonged periods (up to 6 months) causes arterial hypertension accompanied by significant reductions in heart weight, left ventricular weight indexes, and cardiomyocyte size.

Numerical density of cardiomyocytes in chronic nitric oxide synthesis inhibition

OBJECTIVE

The myocardial effect on the normalization of arterial blood pressure in animals with hypertension previously induced by nitric oxide synthesis (NOS) inhibition is still unknown. The purpose of this study was to estimate the numerical density of cardiomyocytes that is able to show cardiomyocyte loss as a consequence of NOS inhibition.

METHODS

Sixty rats were divided into the following groups: control for 25 days (C25), control for 40 days (C40) control for 80 days (C80) and three other groups in which the rats received the NOS inhibitor N(G)-nitro-L-arginine-methyl-ester hydrochloride L-NAME; 50 mg/kg/day for 25 days (L25), 40 days (L40) and 40 days, respectively, the latter group having another 40 days of only water and food ad libitum (without L-NAME; L80 group). The detection of apoptotic cells was performed using a monoclonal antibody.

RESULTS

In the L25, L40 and L80 groups, blood pressure was 74.5, 90.2 and 56.3% higher than the respective age-matched control rats, the myocardium had hypertrophy of the cardiomyocytes and scattered areas of fibrosis, and apoptosis occurred in isolated cells. Compared to the controls, the heart mass/body mass ratio was significantly greater in the L-NAME groups L25, L40 and L80, i.e. 31, 26 and 21%, respectively, the numerical density of cardiomyocytes in L-NAME rats was 32.7, 48.8 and 41.7% lower and the mean volume of cardiomyocytes was 33, 53 and 48% greater.

CONCLUSION

The cardiomyocyte loss in NOS inhibition seems to be mainly due to necrosis, although apoptosis is also present.

Myocardial microcirculation stereological changes in rats subjected to nitric oxide synthesis inhibition

This work aims to study stereological changes in intramyocardial blood vessels in rats submitted to nitric oxide (NO) synthesis inhibition within different periods. NO synthesis inhibition was achieved by administration of L-NAME (50 mg/kg/day); control and L-NAME rats were sacrificed 25 and 40 days after experimentation. Light microscopy and stereology [according to references 7, 13 and 14] were used for analyzing the myocardium. Arterial blood pressure and cardiac weight increased by 74.5% and 57.8% after 25 days and by 90.2% and 34.6% after 40 days, respectively. Comparing the L-NAME rats with corresponding controls revealed that the volume density of the vessels decreased by 31.3% after 40 days, and the length density by 53.5% after 25 days and by 25.7% after 40 days. The mean cross-sectional area of the vessels increased by 154.6% after 25 days. In this study on intramyocardial vessels, we observed an important decrease of the length density in L-NAME animals. Likewise, the volume density also decreased significantly in L-NAME animals. The mean cross sectional area of the vessels, which normally increases during cardiac growth between 25 and 40 days, was precociously increased in L-NAME animals at 25 days, suggesting that these animals suffer from a precocious increase of the heart (including blood vessels) due to pressure overload. Stereology of cardiac microvessels revealed remodeling of these vessels in rats under NO synthesis inhibition. Although these changes may be caused by NO inhibition and not by arterial hypertension, further comparative studies on different models of arterial hypertension are needed to confirm this hypothesis.