ABSTRACT
Baroreflex sensitivity was studied in the same group of conscious rats using vasoactive drugs (phenylephrine and sodium nitroprusside) administered by three different approaches: 1) bolus injection, 2) steady-state (blood pressure (BP) changes produced in steps), 3) ramp infusion (30 s, brief infusion). The heart rate (HR) responses were evaluated by the mean index (mean ratio of all HR changes and mean arterial pressure (MAP) changes), by linear regression and by the logistic method (maximum gain of the sigmoid curve by a logistic function). The experiments were performed on three consecutive days. Basal MAP and resting HR were similar on all days of the study. Bradycardic responses evaluated by the mean index (-1.5 ñ 0.2, -2.1 ñ 0.2 and -1.6 ñ 0.2 bpm/mmHg) and linear regression (-1.8 ñ 0.3, -1.4 ñ 0.3 and -1.7 ñ 0.2 bpm/mmHg) were similar for all three approaches used to change blood pressure. The tachycardic responses to decreases of MAP were similar when evaluated by linear regression (-3.9 ñ 0.8, -2.1 ñ 0.7 and -3.8 ñ 0.4 bpm/mmHg). However, the tachycardic mean index (-3.1 ñ 0.4, -6.6 ñ 1 and -3.6 5 0.5 bpm/mmHg) was higher when assessed by the steady-state method. The average gain evaluated by logistic function (-3.5 ñ 0.6, -7.6 ñ 1.3 and -3.8 ñ 0.4 bpm/mmHg) was similar to the reflex tachycardic values, but different from the bradycardic values. Since different ways to change BP may alter the afferent baroreceptor function, the MAP changes obtained during short periods of time (up to 30 s: bolus and ramp infusion) are more appropriate to prevent the acute resetting. Assessment of the baroreflex sensitivity by mean index and linear regression permits a separate analysis of gain for reflex bradycardia and reflex tachycardia. Although two values of baroreflex sensitivity cannot be evaluated by a single symmetric logistic function, this method has the advantage of better comparing the baroreflex sensitivity of animals with different basal blood pressures
Subject(s)
Animals , Male , Rats , Baroreflex , Blood Pressure Determination/methods , Blood Pressure/physiology , Consciousness , Heart Rate/physiology , Pressoreceptors/physiology , Analysis of Variance , Blood Pressure/drug effects , Bradycardia , Heart Rate/drug effects , Linear Models , Nitroprusside/pharmacology , Phenylephrine/pharmacology , Rats, Wistar , TachycardiaABSTRACT
O objetivo desse estudo foi avaliar a atividade neurogênica dos pressoreceptores (APR, registrada no nervo aórtico) e a atividade simpática periférica (ASR, registrada no nervo simpático renal), considerando-se a ocorrência e distribuição nos ciclos cardíacos e nas fases sistólica e diastólica. Foram estudados ratos normais anestesiados e ratos acordados submetidos à desnervação sino-aórtica (DSA) nas fases aguda e crônica após a desnervação. Os resultados obtidos sugerem que a falta de sincronismo entre a atividade simpática e os ciclos da pressão arterial contribuem para as alterações encontradas na pressão sanguínea na ausência dos pressoreceptores
Abstract - The aim of this study was to analyze the neurogenic activity of baroreceptors (recorded on the aortic nerve, APR) and peripheral sympathetic activity (recorded on the renal nerve. AsR ) with regard to its occurence and distribution in relation to the cardiac cycle and the systolic and diastolic phases of it. Normal anesthetized rats and awaken sino aortic denervated (SAD) rats were studied. The analysis showed that the existing synchronism between sympathetic activity and arterial pressure pulses found in normal rats was absent in SAD rats. These results suggest that the Jack of synchronism between sympathetic activity and cardiac cycles may contribute to the alterations in blood pressure observed in the absence of baroreceptors