João Paulo J. Sabino

The treatment with pyridostigmine improves the cardiocirculatory function in rats with chronic heart failure

Sympathetic hyperactivity and its outcome in heart failure have been thoroughly investigated to determine the focus of pharmacologic approaches targeting the sympathetic nervous system in the treatment of this pathophysiological condition. On the other hand, therapeutic approaches aiming to protect the reduced cardiac parasympathetic function have not received much attention. The present study evaluated rats with chronic heart failure (six to seven weeks after coronary artery ligation) and the effects of an increased parasympathetic function by pyridostigmine (an acetylcholinesterase inhibitor) on the following aspects: arterial pressure (AP), heart rate (HR), baroreceptor and Bezold-Jarisch reflex, pulse interval (PI) and AP variability, cardiac sympathetic and parasympathetic tonus, intrinsic heart rate (i-HR) and cardiac function. Conscious rats with heart failure exhibited no change in HR, Bezold-Jarisch reflex, PI variability and cardiac sympathetic tonus. On the other hand, these animals presented hypotension and reduced baroreflex sensitivity, power in the low frequency (LF) band of the systolic AP spectrum, cardiac parasympathetic tonus and i-HR, while anesthetized rats exhibited reduced cardiac performance. Pyridostigmine prevented the attenuation of all the parameters examined, except basal AP and cardiac performance. In conclusion, the blockade of acetylcholinesterase with pyridostigmine was revealed to be an important pharmacological approach, which could be used to increase parasympathetic function and to improve a number of cardiocirculatory parameters in rats with heart failure.

Resting heart rate as a predictor of metabolic dysfunctions in obese children and adolescents

BackgroundRecent studies have identified that a higher resting heart rate (RHR) is associated with elevated blood pressure, independent of body fatness, age and ethnicity. However, it is still unclear whether RHR can also be applied as a screening for other risk factors, such as hyperglycemia and dyslipidemia. Thus, the purpose of the presented study was to analyze the association between RHR, lipid profile and fasting glucose in obese children and adolescents.MethodsThe sample was composed of 180 obese children and adolescents, aged between 7-16 years. Whole-body and segmental body composition were estimated by Dual-energy X-ray absorptiometry. Resting heart rate (RHR) was measured by heart rate monitors. The fasting blood samples were analyzed for serum triglycerides, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and glucose, using the colorimetric method.ResultsFasting glucose, TC, triglycerides, HDL-C, LDL-C and RHR were similar in both genders. The group of obese subjects with a higher RHR presented, at a lower age, higher triglycerides and TC. There was a significant relationship between RHR, triglycerides and TC. In the multivariate model, triglycerides and TC maintained a significant relationship with RHR independent of age, gender, general and trunk adiposity. The ROC curve indicated that RHR has a high potential for screening elevated total cholesterol and triglycerides as well as dyslipidemia.ConclusionElevated RHR has the potential to identify subjects at an increased risk of atherosclerosis development.

Hemodynamic and ventilatory response to different levels of hypoxia and hypercapnia in carotid body-denervated rats

OBJECTIVE: Chemoreceptors play an important role in the autonomic modulation of circulatory and ventilatory responses to changes in arterial O2 and/or CO2. However, studies evaluating hemodynamic responses to hypoxia and hypercapnia in rats have shown inconsistent results. Our aim was to evaluate hemodynamic and respiratory responses to different levels of hypoxia and hypercapnia in conscious intact or carotid body-denervated rats. METHODS: Male Wistar rats were submitted to bilateral ligature of carotid body arteries (or sham-operation) and received catheters into the left femoral artery and vein. After two days, each animal was placed into a plethysmographic chamber and, after baseline measurements of respiratory parameters and arterial pressure, each animal was subjected to three levels of hypoxia (15, 10 and 6% O2) and hypercapnia (10% CO2). RESULTS: The results indicated that 15% O2 decreased the mean arterial pressure and increased the heart rate (HR) in both intact (n = 8) and carotid body-denervated (n = 7) rats. In contrast, 10% O2 did not change the mean arterial pressure but still increased the HR in intact rats, and it decreased the mean arterial pressure and increased the heart rate in carotid body-denervated rats. Furthermore, 6% O2 increased the mean arterial pressure and decreased the HR in intact rats, but it decreased the mean arterial pressure and did not change the HR in carotid body-denervated rats. The 3 levels of hypoxia increased pulmonary ventilation in both groups, with attenuated responses in carotid body-denervated rats. Hypercapnia with 10% CO2 increased the mean arterial pressure and decreased HR similarly in both groups. Hypercapnia also increased pulmonary ventilation in both groups to the same extent. CONCLUSION: This study demonstrates that the hemodynamic and ventilatory responses varied according to the level of hypoxia. Nevertheless, the hemodynamic and ventilatory responses to hypercapnia did not depend on the activation of the peripheral carotid chemoreceptors.

Endogenous hydrogen sulfide in the rostral ventrolateral medulla/Bötzinger complex downregulates ventilatory responses to hypoxia

Hydrogen sulfide (H2S) is now recognized as a new gaseous transmitter involved in several brain-mediated responses. The rostral ventrolateral medulla (RVLM)/Bötzinger complex is a region in the brainstem that is involved in cardiovascular and respiratory functions. Recently, it has been shown that exogenous H2S in the RVLM modulates autonomic function and thus blood pressure. In the present study, we investigated whether H2S, endogenously produced in the RVLM/Bötzinger complex, plays a role in the control of hypoxia-induced hyperventilation. Ventilation (VE) was measured before and after bilateral microinjection of Na2S (H2S donor, 0.04, 1 and 2 pmol/100 nl) or aminooxyacetate (AOA, 0.2, 1 and 2 pmol/100 nl, a cystathionine β-synthase, CBS, inhibitor) into the RVLM/Bötzinger complex followed by a 60-min period of hypoxia (7% inspired O2) or normoxia exposure. Control rats received microinjection of vehicle. Microinjection of vehicle, AOA or Na2S did not change VE in normoxic conditions. Exposure to hypoxia evoked a typical increase in VE. Microinjection of Na2S (2 pmol) followed by hypoxia exposure attenuated the hyperventilation. Conversely, microinjection of AOA (2 pmol) into the RVLM/Bötzinger complex caused an increase in the hypoxia-induced hyperventilation. Thus, endogenous H2S in the RVLM/Bötzinger complex seems to play no role in the maintenance of basal pulmonary ventilation during normoxia whereas during hypoxia H2S has a downmodulatory function. Homogenates of RVLM/Bötzinger complex of animals previously exposed to hypoxia for 60 min exhibited a decreased rate of H2S production. Our data are consistent with the notion that the gaseous messenger H2S synthesis is downregulated in the RVLM/Bötzinger complex during hypoxia favoring hyperventilation.

Parasympathetic activation by pyridostigmine on chemoreflex sensitivity in heart-failure rats.

We evaluated the effects of parasympathetic activation by pyridostigmine (PYR) on chemoreflex sensitivity in a rat model of heart failure (HF rats). HF rats demonstrated higher pulmonary ventilation (PV), which was not affected by PYR. When HF and control rats treated or untreated with PYR were exposed to 15% O2, all groups exhibited prompt increases in respiratory frequency (RF), tidal volume (TV) and PV. When HF rats were exposed to 10% O2 they showed greater PV response which was prevented by PYR. The hypercapnia triggered by either 5% CO2 or 10% CO2 promoted greater RF and PV responses in HF rats. PYR blunted the RF response in HF rats but did not affect the PV response. In conclusion, PYR prevented increased peripheral chemoreflex sensitivity, partially blunted central chemoreflex sensitivity and did not affect basal PV in HF rats.

Hypoxia-related gene expression profile in childhood acute lymphoblastic leukemia: prognostic implications

Abstract A cellular hypoxic condition is a key event in several human cancers, but knowledge about its role in childhood acute lymphoblastic leukemia (ALL) is very limited. In the present study, the gene expression profile of hypoxia-related genes (HIF1A, CA9, VEGF and SCL2A1) was evaluated in bone marrow samples of 113 pediatric patients. HIF1A mRNA up-regulation was significantly associated with higher 5-year event-free survival rates in patients with B-ALL as well as in the overall ALL population in both univariate and multivariate analysis (p = 0.023 and p = 0.041, respectively). In gene expression analysis, low oxygen levels promoted HIF1A activation in a time-dependent manner, in both ALL cell lines. In vitro cytotoxic assays suggested an initial trend toward hypoxia-related resistance in the first 24 h, but evaluation at later time points (48–72 h) clearly showed that there was no relevant difference in drug response when comparing hypoxic and normal oxygen level conditions. Modulation of mRNA expression of several hypoxia-related genes was also observed after hypoxic exposure in a cell specific manner, suggesting that HIF1A mRNA expression could play a different role in specific subtypes of leukemia. Despite the remaining questions regarding hypoxia-mediated mechanisms, these findings could be helpful to provide new insights into the role of hypoxia in childhood ALL.

Autonomic Modulation and Its Relation With Body Composition in Swimmers

Abstract Rossi, FE, Ricci-Vitor, AL, Sabino, JPJ, Vanderlei, LCM, and Freitas, IF Jr. Autonomic modulation and its relation with body composition in swimmers. J Strength Cond Res 28(7): 2047–2053, 2014—This study compared autonomic modulation in swimmers and non-athletes in relation to body composition. A total of 28 athletes with a mean age of 19.7 ± 2.9 years were evaluated who had at least 2 years of swimming training, trained approximately 7,000 m per day, with a frequency of 5 days per week, and who competed at national level. The control group was made up of 21 volunteers (23.0 ± 2.5 years), who did not practice regular physical activity (<2 hours per week). Body composition was estimated using dual-energy x-ray absorptiometry, and autonomic modulation was assessed by heart rate variability (HRV). The results show that there were significant differences in autonomic modulation and body composition between the groups, and that the athletes had a higher overall variability (standard deviation of all normal intervals between consecutive heart beats [SDNN]: 78.1 [72.5–93.5] × 61.1 [56.4–75.7], p = 0.022) and greater autonomic balance (LF/HF: 0.96 [0.88–1.35] × 0.71 [0.56–0.93], p = 0.023), compared with the non-athletes, respectively. In addition, a moderate and positive relation was obtained between fat-free mass and the square root of the squared differences between consecutive heartbeat intervals (RMSSD: r = 0.526, p = 0.004 × r = 0.456, p = 0.038), (SDNN: r = 0.617, p = 0.001 × r = 0.571, p = 0.007) and low frequency (LFms2: r = 0.517, p = 0.005 × r = 0.600, p = 0.004) in the athletes and non-athletes, respectively, without a correlation between fat mass (FM). The conclusion is that young highly trained swimmers had lower FM, increased fat-free mass, and better HRV than young adult non-athletes and suggests that a lower quantity of FM and, especially, a greater fat-free mass (FFM) are linked to better autonomic modulation. Thus, this study could contribute to coaches and trainers establishing greater performance by better autonomic modulation and greater quantity of FFM.

Involvement of endogenous hydrogen sulfide (H2S) in the rostral ventrolateral medulla (RVLM) in hypoxia-induced hypothermia

Hypoxia evokes a regulated decrease in deep body temperature (Tb). Hydrogen sulfide (H2S), a signaling molecule that belongs to the gasotransmitter family, has been demonstrated to participate in several brain-mediated responses. Rostral ventrolateral medulla (RVLM) is a brainstem region involved in thermoregulation. Recently, it has been shown that exogenous H2S modulates RVLM activity. In the present study, we investigated whether endogenously produced H2S in the RVLM plays a role in the control of hypoxia-induced hypothermia. Tb was measured before and after bilateral microinjection of aminooxyacetate (AOA, 0.2, 1 and 2 pmol/100 nl, a cystathionine β-synthase, CBS, inhibitor) or vehicle into the RVLM followed by a 60-min normoxia (21% inspired O2) or hypoxia (7% inspired O2) exposure. Microinjection of AOA or vehicle did not change Tb during normoxia. Exposure to hypoxia evoked a typical decrease in Tb. Microinjection of AOA (2 pmol) into the RVLM followed by hypoxia significantly attenuated the decrease in Tb. Thus, endogenous H2S in the RVLM seems to play no role in the maintenance of basal Tb, whereas during hypoxia this gas plays a cryogenic role. Moreover, RVLM homogenates of rats exposed to hypoxia exhibited a decreased rate of H2S production. Our data are consistent with the notion that during hypoxia H2S synthesis is diminished in the RVLM facilitating hypothermia.

Role of the spinal cord NO/cGMP pathway in the control of arterial pressure and heart rate.

The modulatory effect of nitric oxide/cyclic guanosine monophosphate (NO/cGMP) pathway on sympathetic preganglionic neurons still deserves further investigation. The present study was designed to examine the role of the spinal cord NO/cGMP pathway in controlling mean arterial pressure and heart rate. We observed that intrathecal administration of the NO synthase inhibitor Nω-Nitro-l-arginine methyl ester hydrochloride (l-NAME) causes an increase in mean arterial pressure but does not affect heart rate. Intrathecal administration of the soluble guanylyl cyclase inhibitor 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) does not change mean arterial pressure and heart rate. The precursor for NO synthesis, l-arginine, reduces both mean arterial pressure and heart rate while administration of ODQ before l-arginine impaired decreases in mean arterial pressure and heart rate. Administration of the N-methyl-d-aspartate (NMDA) receptor antagonist dl-2-amino-5-phosphonopentanoic acid (AP5) after l-NAME does not affect increases in mean arterial pressure promoted by NO synthase inhibition. Although the hypotensive and bradycardic responses induced by intrathecal administration of l-arginine depend on cGMP, our results indicate that NO acts to tonically inhibit SPNs, independent of either cGMP or NMDA receptors.

Role of cGMP and cAMP in the hemodynamic response to intrathecal sildenafil administration.

INTRODUCTION: Results from our laboratory have demonstrated that intracerebroventricular administration of sildenafil to conscious rats promoted a noticeable increase in both lumbar sympathetic activity and heart rate, with no change in the mean arterial pressure. The intracerebroventricular administration of sildenafil may have produced the hemodynamic effects by activating sympathetic preganglionic neurons in the supraspinal regions and spinal cord. It is well documented that sildenafil increases intracellular cGMP levels by inhibiting phosphodiesterase type 5 and increases cAMP levels by inhibiting other phosphodiesterases. OBJECTIVE: To examine and compare, in conscious rats, the hemodynamic response following the intrathecal administration of sildenafil, 8-bromo-cGMP (an analog of cGMP), forskolin (an activator of adenylate cyclase), or dibutyryl-cAMP (an analog of cAMP) in order to elucidate the possible role of the sympathetic preganglionic neurons in the observed hemodynamic response. RESULTS: The hemodynamic responses observed following intrathecal administration of the studied drugs demonstrated the following: 1) sildenafil increased the mean arterial pressure and heart rate in a dose-dependent manner, 2) increasing doses of 8-bromo-cGMP did not alter the mean arterial pressure and heart rate, 3) forskolin did not affect the mean arterial pressure but did increase the heart rate and 4) dibutyryl-cAMP increased the mean arterial pressure and heart rate, similar to the effect observed following the intrathecal injection of the highest dose of sildenafil. CONCLUSION: Overall, the findings of the current study suggest that the cardiovascular response following the intrathecal administration of sildenafil to conscious rats involves the inhibition of phosphodiesterases other than phosphodiesterase type 5 that increase the cAMP level and the activation of sympathetic preganglionic neurons.