Cardiac baroreflex is already blunted in eight weeks old spontaneously hypertensive rats

Background. The literature did not evidence yet with which age spontaneously hypertensive rats (SHR) start to present baroreflex reduction. We endeavored to evaluate the baroreflex function in eight-week-old SHR. Methods. Male Wistar Kyoto (WKY) normotensive rats and SHR aged eight weeks were studied. Baroreflex was calculated as the variation of heart rate (HR) divided by the mean arterial pressure (MAP) variation (HR/MAP) tested with a depressor dose of sodium nitroprusside (SNP, 50 g/kg) and with a pressor dose of phenylephrine (PHE, 8 g/kg) in the right femoral venous approach through an inserted cannula in the animals. Significant differences for p < 0.05. Results. Baseline MAP (p < 0.0001) and HR (p = 0.0028) was higher in SHR. Bradycardic peak was attenuated in SHR (p < 0.0001), baroreflex gain tested with PHE was also reduced in the SHR group (p = 0.0012). PHE-induced increase in MAP was increased in WKY compared to SHR (p = 0.039). Bradycardic reflex responses to intravenous PHE was decreased in SHR (p < 0.0001). Conclusion. Eight weeks old SHR already presents impairment of the parasympathetic component of baroreflex. © 2010 Cisternas et al; licensee BioMed Central Ltd.

Effect of the Single or Combined Administration of Cocaine and Testosterone on Cardiovascular Function and Baroreflex Activity in Unanesthetized Rats

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

Lateral septal area alpha(1)-and alpha(2)-adrenoceptors differently modulate baroreflex activity in unanaesthetized rats

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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.

Temperature effects on baroreflex control of heart rate in the toad, Rhinella schneideri

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

Chemoreflex and baroreflex alterations in Parkinsonism induced by 6-OHDA in unanesthetized rats

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)