Role of nitric oxide in mediating cardiovascular alterations accompanying heart failure in rats

Vena cava presents endothelial dysfunction prior to thoracic aorta in heart failure: the pivotal role of nNOS uncoupling/oxidative stress

Arterial endothelial dysfunction has been extensively studied in heart failure (HF). However, little is known about the adjustments shown by the venous system in this condition. Considering that inferior vena cava (VC) tone could influence cardiac performance and HF prognosis, the aim of the present study was to assess the VC and thoracic aorta (TA) endothelial function of HF-post-myocardial infarction (MI) rats, comparing both endothelial responses and signaling pathways developed. Vascular reactivity of TA and VC from HF post-MI and sham operated (SO) rats was assessed with a wire myograph, 4 weeks after coronary artery occlusion surgery. Nitric oxide (NO), H2O2 production and oxidative stress were evaluated in situ with fluorescent probes, while protein expression and dimer/monomer ratio was assessed by Western blot. VC from HF rats presented endothelial dysfunction, while TA exhibited higher acetylcholine (ACh)-induced vasodilation when compared with vessels from SO rats. TA exhibited increased ACh-induced NO production due to a higher coupling of endothelial and neuronal NO synthases isoforms (eNOS, nNOS), and enhanced expression of antioxidant enzymes. These adjustments, however, were absent in VC of HF post-MI rats, which exhibited uncoupled nNOS, oxidative stress and higher H2O2 bioavailability. Altogether, the present study suggests a differential regulation of endothelial function between VC and TA of HF post-MI rats, most likely due to nNOS uncoupling and compromised antioxidant defense.

Role of calcium channels responsible for phenylephrine-induced contraction in rat aorta 3 days after acute myocardial infarction

Background

Phenylephrine (PE) produces tonic contraction through involvement of various calcium channels such as store-operated calcium channels (SOCCs) and voltage-operated calcium channels (VOCCs). However, the relative contribution of each calcium channel to PE-induced contraction has not been investigated in isolated rat aorta of early acute myocardial infarction (AMI).

Methods

Endothelium-denuded rat aortic rings from rats 3 days after AMI or sham-operated (SHAM) rats were prepared in an organ chamber with Krebs-Ringer bicarbonate solution for isometric tension recording. We assessed the PE dose-response relationships in 2.5 mM calcium medium for both groups. The same procedure was repeated using rings pretreated with the SOCC inhibitor 2-aminoethoxydiphenyl borate, sarco/endoplasmic-reticulum calcium ATPase inhibitor thapsigargin (TG), diacyl glycerol lipase inhibitor RHC80267, and sodium-calcium exchanger inhibitor 3,4-dichlorobenzamil hydrochloride for 30 minutes before addition of calcium. When ongoing tonic contraction was sustained, dose-response curves to the VOCC inhibitor nifedipine were obtained to assess the relative contribution of each calcium channel under various conditions.

Results

The effect of SOCC induction with TG pretreatment on PE-induced contraction was significantly lower in the AMI group compared to the SHAM group. In addition, there were significant decreases in the sensitivity and efficacy of the VOCC inhibitor nifedipine on PE-induced contraction in the AMI group.

Conclusions

Results suggest that the change of vascular reactivity of PE in rat aorta 3 days after AMI is characterized by a decreased contribution of L-type VOCCs. The enhanced VOCC-independent calcium entry mechanisms after AMI can be mediated by enhanced capacitative calcium entry through the activation of SOCCs.

Is nitric oxide a mediator of the effects of low-intensity electrical stimulation on bone in ovariectomized rats?

Low-intensity electrical stimulation (LIES) may counteract the effects of ovariectomy (OVX) on nitric oxide synthase (NOS) expression, osteocyte viability, bone structure, and microarchitecture in rats (Lirani-Galvão et al., Calcif Tissue Int 84:502-509, 2009). The aim of the present study was to investigate if these effects of LIES could be mediated by NO. We analyzed the effects of NO blockage (by L-NAME) in the response to LIES on osteocyte viability, bone structure, and microarchitecture in OVX rats. Sixty rats (200-220 g) were divided into six groups: sham, sham-L-NAME (6 mg/kg/day), OVX, OVX-L-NAME, OVX-LIES, and OVX-LIES-L-NAME. After 12 weeks, rats were killed and tibiae collected for histomorphometric analysis and immunohistochemical detection of endothelial NOS (eNOS), inducible NOS (iNOS), and osteocyte apoptosis (caspase-3 and TUNEL). In the presence of L-NAME, LIES did not counteract the OVX-induced effects on bone volume and trabecular number (as on OVX-LIES). L-NAME blocked the stimulatory effects of LIES on iNOS and eNOS expression of OVX rats. Both L-NAME and LIES decreased osteocyte apoptosis. Our results showed that in OVX rats L-NAME partially blocks the effects of LIES on bone structure, turnover, and expression of iNOS and eNOS, suggesting that NO may be a mediator of some positive effects of LIES on bone.

Functional alterations in NO, PGI2and EDHF pathways in the aortic endothelium after myocardial infarction in rats

BACKGROUND

Previous work on endothelial dysfunction in post-MI heart failure has shown conflicting results.

AIM

To analyze gender related alterations in NO-, PGI(2)- and EDHF-dependent endothelial function in the thoracic aorta 7 and 42 days after myocardial infarction (MI).

METHODS AND RESULTS

MI was induced by coronary artery ligation in female and male Sprague-Dawley rats. There was no gender related difference in infarct-size or in the impairment of fractional shortening of the left ventricle 42 days after coronary ligation. Neither acetylcholine-induced (Ach) vasodilation nor basal PGI(2) production in the aorta was modified by coronary ligation. Interestingly, 7 days after MI, basal NO production was impaired and the EDHF component of Ach-induced vasodilation was up-regulated, in both male and female rats. However, 42 days post-MI, basal NO was only impaired in male rats, while EDHF was only up-regulated in female rats.

CONCLUSION

MI induced impairment of functional activity of basal NO production and adaptive up-regulation of the EDHF component of Ach-induced relaxation. The above alterations in endothelial function in the aorta were gender-specific at 42 days but not 7 days after MI. Some of the previously reported discrepancies in the development of endothelial dysfunction in the post-MI period may be gender related differences.

Increased vascular angiotensin II binding capacity and ET-1 release in young cardiomyopathic hamsters

Heart failure (HF) is a multifactorial and progressive disease that has been associated with multiple systemic and vascular alterations. Previous reports from our laboratory showed that in 2-month-old Bio-To2 Syrian cardiomyopathic hamsters (SCH) that have not yet developed the clinical manifestations of HF, the vascular contractility induced by 0.1 microM angiotensin II was approximately 35% greater than in control animals. This finding was observed concomitantly with an increased aortic ACE activity. To further evaluate the mechanisms underlying angiotensin II-enhanced vascular contraction, concentration-response curves for angiotensin II (0.01 nM-10 microM) were constructed before and after the addition of prazosin (alpha-1 blocker), NS-398 (selective COX-2 blocker) and BQ-123 (ET-1A-receptor antagonist) in aortic rings from 2-month-old SCH. The binding capacity and affinity of the AT-1 receptors were also evaluated in aortic homogenates using 125I-angiotensin II. Age-matched golden hamsters were used as controls (CT). Our results indicate that incubation with either 10 microM prazosin or 10 microM NS-398 did not modify EC50 or Emax values for angiotensin II indicating that norepinephrine and prostaglandins are not involved in the enhanced contractile action of angiotensin II. However, 10 microM BQ-123 reduced by 40% the contraction induced by 1.0 microM angiotensin II (from 1.05+/-0.04 to 0.6475+/-0.06 g/mg tissue, n = 5, P < 0.05), suggesting that in cardiomyopathic hamsters, the action of angiotensin II is mediated in part by ET-1. At lower angiotensin II concentration (0.1 microM), the ET-1-dependent contraction decreases to 29%. In addition, although dissociation constants for labeled angiotensin II were found to be similar in the aorta of SCH and control animals (K(D): CT = 7.8 nM and SCH = 5.1 nM), 125I-angiotensin II binding capacity was about 2-fold greater in SCH than in controls (Bmax: SCH = 1113 and CT = 605 fmol/mg protein). Altogether these results suggest that in 2-month-old SCH the enhanced response of angiotensin II in the vasculature is mediated both by an increased binding capacity for the hormone and facilitation of the ET-1 action.

Effects of Inducible Nitric Oxide Synthase Inhibition on the Rat Tail Vascular Bed Reactivity Three Days After Myocardium Infarction

The acute phase of myocardial infarction promotes an inflammatory response that stimulates inducible nitric oxide synthase (iNOS). We investigated the iNOS role on the rat tail vascular bed reactivity 3 days after myocardial infarction. Vasodilator and vasoconstrictor responses were determined in isolated caudal vascular beds from Wistar rats 3 days after coronary artery ligation (CAL) and sham-operated animals (SHAM). Rats were treated with the iNOS inhibitor S-methylisothiourea sulfate (SMT), 5 mg Kg day, i.p. or placebo. Concentration of plasma nitrite/nitrate (NOx) and the expression of iNOS mRNA in tail arteries were evaluated. The CAL group showed increased maximal vasoconstrictor response to phenylephrine (SHAM= 241 +/- 8; CAL= 288 +/- 13 mm Hg, P < 0.05) and SMT treatment normalized this effect (CAL-SMT = 253 +/- 7 mm Hg, P < 0.05). The sensitivity to acetylcholine was reduced in the CAL group, but SMT treatment did not alter this response. The plasma NOx and iNOS mRNA expression in tail arteries were increased in CAL rats. SMT treatment reduced the plasma NOx in the CAL group and the arterial expression of iNOS mRNA in SHAM and CAL group. In conclusion, iNOS inhibition prevented the increased phenylephrine reactivity in rat caudal vascular beds 3 days after myocardial infarction.