EFFECT OF ENALAPRIL TREATMENT ON THE SENSITIVITY OF CARDIOPULMONARY REFLEXES IN RATS WITH MYOCARDIAL INFARCTION

Intermittent exposure to chlorpyrifos results in cardiac hypertrophy and oxidative stress in rats

Forbidden in some countries due to its proven toxicity to humans, chlorpyrifos (CPF) still stands as an organophosphate pesticide (OP) highly used worldwide. Cardiotoxicity assessment is an unmet need in pesticide regulation and should be deeply studied through different approaches to better inform and generate an appropriate regulatory response to OP use. In the present study, we used our 4-week intermittent OP exposure model in rats to address the CPF effects on cardiac morphology allied with cardiovascular functional and biomolecular evaluation. Rats were intermittently treated with CPF at doses of 7 mg/kg and 10 mg/kg or saline (i.p.) and assessed for cardiac morphology (cardiomyocyte diameter and collagen content), cardiopulmonary Bezold-Jarisch reflex (BJR) function, cardiac autonomic tone, left ventricle (LV) contractility, cardiac expression of NADPH oxidase (Nox2), catalase (CAT), superoxide dismutase 1 (SOD1), superoxide dismutase 2 (SOD2) and cardiac levels of advanced oxidation protein products (AOPP) and thiobarbituric acid reactive substances (TBARS). Plasma butyrylcholinesterase (BuChE) and brainstem acetylcholinesterase (AChE) were also measured. Intermittent exposure to CPF induced cardiac hypertrophy, increasing cardiomyocyte diameter and collagen content. An impairment of cardioinhibitory BJR responses and an increase in cardiac vagal tone were also observed in CPF-treated animals without changes in LV contractility. CPF exposure increased cardiac Nox-2, CAT, SOD1, and TBARS levels and inhibited plasma BuChE and brainstem AChE activities. Our data showed that intermittent exposure to CPF induces cardiac hypertrophy together with cardiovascular reflex impairment, imbalance of autonomic tone and oxidative stress, which may bring significant cardiovascular risk to individuals exposed to OP compounds seasonally.

Cardiovascular autonomic modulation by nitric oxide synthases accounts for the augmented enalapril-evoked hypotension in ethanol-fed female rats

In this study, we investigated the role of nitric oxide synthase (NOS) isoforms in the enhanced enalapril-evoked hypotension in ethanol-fed female rats by examining the effect of the selective inhibitors of eNOS [N(5)-(1-iminoethyl)-l-ornithine; l-NIO], nNOS (N(ω)-propyl-l-arginine; NPLA), or iNOS (1400W) inhibition on the cardiovascular effects of enalapril in ethanol- (5% w/v) fed rats and in their pair-fed controls. In liquid diet-fed control rats, enalapril- (10 mg/kg) evoked hypotension was abolished by l-NIO (20 mg/kg), but not by NPLA (1 mg/kg) or 1400W (5 mg/kg), suggesting a preferential role for eNOS in this response. Enalapril had no effect on spectral indices of hemodynamic variability or +dP/dtmax (myocardial contractility). However, in ethanol-fed rats, the greater enalapril-evoked hypotension was associated with reductions in (i) +dP/dtmax, (ii) low-frequency/high-frequency ratio of interbeat intervals (IBILF/HF), suggesting cardiac parasympathetic dominance, and (iii) low-frequency spectral band of systolic blood pressure (BP), a marker of vasomotor sympathetic tone. While NPLA or 1400W attenuated the enalapril-evoked hemodynamic and autonomic responses in ethanol-fed rats, l-NIO virtually abolished the hypotensive response and was more efficacious in rectifying autonomic responses to enalapril. Together, these findings implicate NOS isoforms, particularly eNOS, in the altered cardiovascular autonomic control that leads to the augmented enalapril-evoked hypotension in ethanol-fed female rats.

Nandrolone decanoate determines cardiac remodelling and injury by an imbalance in cardiac inflammatory cytokines and ACE activity, blunting of the Bezold-Jarisch reflex, resulting in the development of hypertension

The aims of this study were to evaluate the effects of nandrolone (ND) on cardiac inflammatory cytokines, ACE activity, troponin I, and the sensitivity of the Bezold-Jarisch reflex (BJR). Male Wistar rats were administered either ND (20 mg/kg; DECA) or vehicle (control animals; CONT) for 4 weeks. BJR was analyzed by measuring the bradycardia and hypotension responses elicited by serotonin administration (2-32 μg/kg). Mean arterial pressure (MAP) was assessed and myocyte hypertrophy was determined by the heart weight/body weight ratio and by morphometric analysis. Matrix collagen deposition was assessed by histological analysis of the picrosirius red-stained samples. Mesenteric vascular reactivity was performed and central venous pressure (CVP) evaluated. Cardiac inflammatory cytokine levels and angiotensin-converting enzyme (ACE) activity were studied as well the biomarker of cardiac lesion, troponin I. DECA group showed enhancement of matrix type I collagen deposition (p < 0.01) and cardiac ACE activity (p < 0.01) compared with the CONT. Interleukin (IL)-10 was reduced (p < 0.01) and pro-inflammatory cytokines (TNF-α and IL-6; p < 0.01) were increased in the DECA group compared with CONT. Cardiac injury was observed in the DECA group shown by the reduction in cardiac troponin I (p < 0.01) compared with the CONT group. Animals in the DECA group also developed myocyte hypertrophy and reduction of BJR sensitivity. The MAP of animals treated with ND reached hypertensive levels (p < 0.01; compared with CONT). No changes in CVP and vascular reactivity were observed in both experimental groups. We conclude that high doses of ND elicit cardiotoxic effects with cardiac remodelling and injury. Cardiac changes reduce the BJR sensitivity. Together, these abnormalities contributed to the development of hypertension in animals in the DECA group.

Role of the renin–angiotensin system in the nandrolone-decanoate-induced attenuation of the Bezold–Jarisch reflex

The androgen nandrolone decanoate (ND) is known to cause cardiovascular abnormalities, such as attenuation of the Bezold–Jarisch Reflex (BJR), cardiac hypertrophy, and elevation of mean arterial pressure (MAP). Futhermore, a relationship between androgens and the renin–angiotensin system (RAS) has been reported. The purpose of this study was to evaluate the influence of RAS on the BJR, cardiac and prostatic hypertrophy, and MAP evoked by ND. For this, male Wistar rats were treated with ND (10 mg·(kg body mass)–1 for 8 weeks; DECA), or vehicle (control animals; CON), or enalapril (10 mg·(kg body mass)–1, daily; CONE), or ND and enalapril (10 mg ND + 10 mg enalapril per kilogram of body mass; DECAE). After 8 weeks of treatment, the BJR was evaluated by bradycardia and hypotensive responses that were elicited by serotonin administration (2–32 µg·(kg body mass)–1). MAP was assessed; cardiac and prostate hypertrophy were determined by the ratio of the tissue mass:body mass, and by histological analysis of the heart. Animals from the DECA group showed prostatic and cardiac hypertrophy, elevation in mean arterial pressure, and an impairment of BJR. Co-treatment with enalapril inhibited these changes. The data from the present study suggest that RAS has an impact on BJR attenuation, cardiac and prostatic hypertrophy, and the elevation in MAP evoked by ND.

Altered cardiovascular reflexes responses in conscious Angiotensin-(1-7) receptor Mas-knockout mice

This study evaluated the physiological importance of Angiotensin-(1-7) receptor Mas on reflex control of circulation. Experiments were performed in male Mas-knockout (Mas-KO) and Wild Type (WT) conscious mice (12-20 wk of age). Baroreceptor reflex was evaluated by the bradycardic response induced by phenylephrine (0.25 μg/5 μl, i.v.). Bezold-Jarisch reflex was evaluated by phenylbiguanide (0.5 μg/5 μl, i.v.) and chemoreflex by potassium cyanide (2.5 μg/5 μl, i.v.). Baseline mean arterial pressure was higher in Mas-KO (n=14) as compared with WT mice (n=18) (118±1 mmHg vs. 109±2 mmHg); however, heart rate was similar in both strains (615±30 bpm vs. 648±13 bpm). Baroreflex bradycardia was lower (0.78±0.44 ms/mmHg vs. 1.30±0.14 ms/mmHg) in Mas-KO compared with WT mice. The depressor (-17±5 mmHg vs. -45±6 mmHg) and bradycardic (-212±36 bpm vs. -391±29 bpm) components of the Bezold-Jarisch reflex were also lower in Mas-KO mice. In addition, chemoreflex pressor response (+20±3 mmHg vs. +12±0.8 mmHg) and bradycardic response (-250±74 bpm vs. -52±26 bpm) were significantly higher in Mas-KO. These results further advances previous studies by showing that the lack of Mas receptor induced important imbalance in the neural control of blood pressure, altering not only the baroreflex but also the chemo- and Bezold-Jarisch reflexes.