Nitric oxide and L-type calcium channel influences the changes in arterial blood pressure and heart rate induced by central angiotesin II

We study the voltage dependent calcium channels and nitric oxide involvement in angiotensin II-induced pressor effect. The antipressor action of L-Type calcium channel antagonist, nifedipine, has been studied when it was injected into the third ventricle prior to angiotensin II. The influence of nitric oxide on nifedipine antipressor action has also been studied by utilizing N(W)-nitro-L-arginine methyl ester (LNAME) (40 mu g/0.2 mu l) a nitric oxide synthase inhibitor and L-arginine ( 20 mu g/0.2 mu l), a nitric oxide donor agent. Adult male Holtzman rats weighting 200-250 g, with cannulae implanted into the third ventricle were injected with angiotensin II. Angiotensin II produced an elevation in mean arterial pressure and a decreased in heart rate. Such effects were potentiated by the prior injection of LNAME. L-arginine and nifedipine blocked the effects of angiotensin II. These data showed the involvement of L-Type calcium channel and a free radical gas nitric oxide in the central control of angiotensin II-induced pressor effect. This suggested that L-Type calcium channel of the circunventricular structures of central nervous system participated in both short and long term neuronal actions of ANG II with the influence of nitrergic system.

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

Background: Recent 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.Methods: The 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.Results: Fasting 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.Conclusion: Elevated RHR has the potential to identify subjects at an increased risk of atherosclerosis development.

POSITIONING DURING RESISTANCE ELBOW FLEXOR EXERCISE AFFECTS ELECTROMYOGRAPHIC ACTIVITY, HEART RATE, and PERCEIVED EXERTION

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Autonomic control of heart rate during forced activity and digestion in the snake Boa constrictor

Reptiles, particularly snakes, exhibit large and quantitatively similar increments in metabolic rate during muscular exercise and following a meal, when they are apparently inactive. The cardiovascular responses are similar during these two states, but the underlying autonomic control of the heart remains unknown. We describe both adrenergic and cholinergic tonus on the heart during rest, during enforced activity and during digestion (24-36h after ingestion of 30% of their body mass) in the snake Boa constrictor. The snakes were equipped with an arterial catheter for measurements of blood pressure and heart rate, and autonomic tonus was determined following infusion of the beta -adrenergic antagonist propranolol (3mg kg(-1)) and the muscarinic cholinoceptor antagonist atropine (3 mg kg-1).The mean heart rate of fasting animals at rest was 26.4 +/- 1.4 min(-1), and this increased to 36.1 +/- 1.4 min(-1) (means +/- S.E.M.; N=8) following double autonomic block (atropine and propranolol). The calculated cholinergic and adrenergic tones were 60.1 +/- 0.3% and 19.8 +/- 2.2%, respectively. Heart rate increased to 61.4 +/- 1.5 min(-1) during enforced activity, and this response was significantly reduced by propranolol (maximum values of 35.8 +/-1.6 min(-1)), but unaffected by atropine. The cholinergic and adrenergic tones were 2.6 +/- 2.2 and 41.3 +/- 1.9 % during activity, respectively. Double autonomic block virtually abolished tachycardia associated with enforced activity (heart rate increased significantly from 36.1 +/- 1.4 to 37.6 +/- 1.3 min(-1)), indicating that non-adrenergic, non-cholinergic effectors are not involved in regulating heart rate during activity. Blood pressure also increased during activity.Digestion was accompanied by an increase in heart rate from 25.6 +/- 1.3 to 47.7 +/- 2.2 min(-1) (N=8). In these animals, heart rate decreased to 44.2 +/- 2.7 min-1 following propranolol infusion and increased to 53.9 +/- 1.8 min-1 after infusion of atropine, resulting in small cholinergic and adrenergic tones (6.0 +/- 3.5 and 11.1 +/- 1.1 %, respectively). The heart rate of digesting snakes was 47.0 +/- 1.0 min(-1) after double autonomic blockade, which is significantly higher than the value of 36.1 1.4 min-1 in double-blocked fasting animals at rest. Therefore, it appears that some other factor exerts a positive chronotropic effect during digestion, and we propose that this factor may be a circulating regulatory peptide, possibly liberated from the gastrointestinal system in response to the presence of food.

Baroreflex control of heart rate in the broad-nosed caiman Caiman latirostris is temperature dependent

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Autonomic control of heart rate is virtually independent of temperature but seems related to the neuroanatomy of the efferent vagal supply to the heart in the bullfrog, Lithobathes catesbeianus

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Role of nitric oxide of the median preoptic nucleus (MnPO) in the alterations of salivary flow, arterial pressure and heart rate induced by injection of pilocarpine into the MnPO and intraperitoneally

We investigated the effect of L-NAME, a nitric oxide (NO) inhibitor and sodium nitroprusside (SNP), an NO-donating agent, on pilocarpine-induced alterations in salivary flow, mean arterial blood pressure (MAP) and heart rate (HR) in rats. Male Holtzman rats (250-300 g) were implanted with a stainless steel cannula directly into the median preoptic nucleus (MnPO). Pilocarpine (10, 20, 40, 80, 160 µg) injected into the MnPO induced an increase in salivary secretion (P<0.01). Pilocarpine (1, 2, 4, 8, 16 mg/kg) ip also increased salivary secretion (P<0.01). Injection of L-NAME (40 µg) into the MnPO prior to pilocarpine (10, 20, 40, 80, 160 µg) injected into the MnPO or ip (1, 2, 4, 8, 16 mg/kg) increased salivary secretion (P<0.01). SNP (30 µg) injected into the MnPO or ip prior to pilocarpine attenuated salivary secretion (P<0.01). Pilocarpine (40 µg) injection into the MnPO increased MAP and decreased HR (P<0.01). Pilocarpine (4 mg/kg body weight) ip produced a decrease in MAP and an increase in HR (P<0.01). Injection of L-NAME (40 µg) into the MnPO prior to pilocarpine potentiated the increase in MAP and reduced HR (P<0.01). SNP (30 µg) injected into the MnPO prior to pilocarpine attenuated (100%) the effect of pilocarpine on MAP, with no effect on HR. Administration of L-NAME (40 µg) into the MnPO potentiated the effect of pilocarpine injected ip. SNP (30 µg) injected into the MnPO attenuated the effect of ip pilocarpine on MAP and HR. The present study suggests that in the rat MnPO 1) NO is important for the effects of pilocarpine on salivary flow, and 2) pilocarpine interferes with blood pressure and HR (side effects of pilocarpine), that is attenuated by NO.

Effects of topical levobunolol or fixed combination of dorzolamide-timolol or association of dorzolamide-levobunolol on intraocular pressure, pupil size, and heart rate in healthy cats

Estudaram-se e compararam-se os efeitos do levobunolol, da combinação fixa de dorzolamida 2%-timolol 0,5% e da associação de dorzolamida 2% com levobunolol 0,5% sobre a pressão intra-ocular (PIO), o diâmetro pupilar (DP), a freqüência cardíaca (FC) e a hiperemia conjuntival em 18 gatos saudáveis. PIO, DP, FC e hiperemia conjuntival foram aferidos diariamente, em três horários distintos (9h, 14h e 18h). Três grupos foram formados (n=6) e um olho de cada animal recebeu, aleatoriamente, uma gota de levobunolol (L), ou a combinação comercial à base de dorzolamida-timolol (DT), ou a associação de dorzolamida com levobunolol (DL). Parâmetros basais foram aferidos no primeiro dia (dia 0). Nos quatro dias consecutivos, os fármacos foram instilados às 8h e 20h e os parâmetros aferidos nos mesmos horários. Todos os parâmetros decresceram significativamente em relação aos valores basais (P<0,001) e não se observou hiperemia conjuntival. O levobunolol reduziu significativamente a PIO, o DP e a FC e o foi o fármaco que mais reduziu a FC. Não se observou efeito sinérgico na redução da PIO quando a dorzolamida foi adicionada ao levobulol.

Relationships and significance of lactate minimum, critical velocity, heart rate deflection and 3 000 m track-tests for running

The running velocities associated to lactate minimum (V-lm), heart rate deflection (V-HRd), critical velocity (CV), 3000 M (V-3000) and 10000 m performance (V-10km) were compared. Additionally the ability of V-lm and VHRd on identifying sustainable velocities was investigated.Methods. Twenty runners (28.5 +/- 5.9 y) performed 1) 3000 m running test for V3000; 2) an all-out 500 in sprint followed by 6x800 m incremental bouts with blood lactate ([lac]) measurements for V-lm; 3) a continuous velocity-incremented test with heart rate measurements at each 200 m for V-HRd; 4) participants attempted to 30 min of endurance test both at V-lm(ETVlm) and V-HRd(ETVHRd). Additionally, the distance-time and velocity-1/time relationships produced CV by 2 (500 m and 3000 m) or 3 predictive trials (500 m, 3000 m and distance reached before exhaustion during ETVHRd), and a 10 km race was recorded for V-10km.Results. The CV identified by different methods did not differ to each other. The results (m(.)min(-1)) revealed that V-.(lm) (281 +/- 14.8)< CV (292.1 +/- 17.5)=V-10km (291.7 +/- 19.3)< V-HRd (300.8 +/- 18.7)=V-3000 (304 +/- 17.5) with high correlation among parameters (P < 0.001). During ETVlm participants completed 30 min of running while on the ETVHRd they lasted only 12.5 +/- 8.2 min with increasing [lac].Conclusion. We evidenced that CV and Vim track-protocols are valid for running evaluation and performance prediction and the parameters studied have different significance. The V-lm reflects the moderate-high intensity domain (below CV), can be sustained without [lac] accumulation and may be used for long-term exercise while the V-HRd overestimates a running intensity that can be sustained for long-time. Additionally, V-3000 and V-HRd reflect the severe intensity domain (above CV).

Evidence for a respiratory component, similar to mammalian respiratory sinus arrhythmia, in the heart rate variability signal from the rattlesnake, Crotalus durissus terrificus

Autonomic control of heart rate variability and the central location of vagal preganglionic neurones (VPN) were examined in the rattlesnake ( Crotalus durissus terrificus), in order to determine whether respiratory sinus arrhythmia (RSA) occurred in a similar manner to that described for mammals. Resting ECG signals were recorded in undisturbed snakes using miniature datalogging devices, and the presence of oscillations in heart rate (f(H)) was assessed by power spectral analysis (PSA). This mathematical technique provides a graphical output that enables the estimation of cardiac autonomic control by measuring periodic changes in the heart beat interval. At fH above 19 min(-1) spectra were mainly characterised by low frequency components, reflecting mainly adrenergic tonus on the heart. By contrast, at f(H) below 19 min(-1) spectra typically contained high frequency components, demonstrated to be cholinergic in origin. Snakes with a f(H) > 19 min(-1) may therefore have insufficient cholinergic tonus and/or too high an adrenergic tonus acting upon the heart for respiratory sinus arrhythmia ( RSA) to develop. A parallel study monitored f(Hd) simultaneously with the intraperitoneal pressures associated with lung inflation. Snakes with a fH < 19 min(-1) exhibited a high frequency (HF) peak in the power spectrum, which correlated with ventilation rate (f(V)). Adrenergic blockade by propranolol infusion increased the variability of the ventilation cycle, and the oscillatory component of the f(H) spectrum broadened accordingly. Infusion of atropine to effect cholinergic blockade abolished this HF component, confirming a role for vagal control of the heart in matching f(H) and f(V) in the rattlesnake. A neuroanatomical study of the brainstem revealed two locations for vagal preganglionic neurones (VPN). This is consistent with the suggestion that generation of ventilatory components in the heart rate variability (HRV) signal are dependent on spatially distinct loci for cardiac VPN. Therefore, this study has demonstrated the presence of RSA in the HRV signal and a dual location for VPN in the rattlesnake. We suggest there to be a causal relationship between these two observations.

Vagal control of heart rate and cardiac shunts in reptiles: Relation to metabolic state

The vagus is clearly of primary importance in the regulation of reptilian cardiorespiratory systems. Vagal control of pulmonary blood flow and cardiac shunts provides reptiles with an additional means of regulating arterial oxygen levels that is not present in endothermic vertebrates (birds and mammals). Within a given species, there exists a clear correlation between withdrawal of vagal tone on the cardiovascular system and elevated metabolic rate. Undisturbed and resting reptiles are normally characterised by high vagal tone, low pulmonary blood flow and large right-left (R-L) cardiac shunts. The low oxygen levels that result from the large R-L shunt may serve to regulate metabolism. However, when metabolism is increased by temperature, exercise or digestion, the R-L cardiac shunt is reduced, which serves to increase oxygen delivery. This response is partially elicit ed by reduction of vagal tone. Interspecies comparisons reveal a similar pattern. Thus, species that are able to sustain the highest metabolic rates possess the highest degree of anatomical ventricular separation and, therefore, less cardiac shunting. It is interesting to note that when cardiac shunts occur in mammals, due for example to developmental defects, they are associated with reduced maximal metabolic rates and impaired exercise tolerance. It appears, therefore, that full separation of ventricular blood flows was a prerequisite for the evolution of high aerobic metabolic rates and exercise stamina in mammals and birds.

DIFFERENT EFFECTS ON RAT ARTERIAL-PRESSURE AND HEART-RATE WHEN LOSARTAN IS INJECTED INTO THE 3RD-VENTRICLE OR 4TH-VENTRICLE

Cardiovascular responses to central losartan (LOS), a non-peptide angiotensin II (ANG II) receptor antagonist, were investigated by comparing the effects of LOS injection into the 3rd and 4th cerebral ventricles (3rdV, 4thV) on mean arterial pressure (MAP) and heart rate (HR). Adult male Holtzman rats were used (N = 6 animals per group). Average basal MAP and HR were 114 +/- 3 mmHg and 343 +/- 9 bpm (N = 23), respectively. LOS (50, 100 or 200 nmol/2 mu l) injected into the 3rdV induced presser (peak of 25 +/- 3 mmHg) and tachycardic (peak of 60 +/- 25 bpm) responses. LOS injected into the 4thV had no effect on MAP, but it induced bradycardia (peak of -35 +/- 15 bpm). KCl (200 nmol/2 mu l) injected into the 3rdV or into the 4thV had no effect on either MAP or HR compared to 0.9% saline injection. The results indicate that LOS injected into the third ventricle acts on forebrain structures to induce its presser and tachycardic effects and that bradycardia, likely dependent on hindbrain structures, is obtained when LOS is injected into the fourth ventricle.