Dynamic exercise shifts the operating point and reduces the gain of the arterial baroreflex in rats

Abstract

We tested the hypothesis that dynamic exercise resets the operating point and attenuates the gain of the arterial baroreflex regulation of heart rate (HR) in rats. Seven adult female spontaneously hypertensive rats (SHR) were chronically instrumented with left carotid arterial catheters. After the rats recovered, arterial baroreflex function was examined by recording reflex changes in HR in response to spontaneous changes in arterial pressure (AP) during a preexercise condition and during steady-state treadmill running at 6 and 18 m/min. Dynamic exercise at 6 and 18 m/min, respectively, reduced the spontaneous range (by 55 and 70%) and spontaneous gain (by 64 and 82%) of the arterial baroreflex control of HR. Dynamic exercise at 6 and 18 m/min, respectively, also increased the pressure at the midpoint of the spontaneous pressure range (by 7 and 12%), the spontaneous minimum HR response (by 35 and 59%), the HR at the midpoint of the spontaneous HR range (by 31 and 52%), and the spontaneous maximum HR response (by 27 and 46%). Sinoaortic denervation eliminated the relationship between AP and HR by reducing the spontaneous gain 95%. These results demonstrate that dynamic exercise shifted the operating point of the arterial baroreflex to a higher pressure and reduced the spontaneous gain in female SHR.

Enhanced baroreflex sensitivity in free-moving calponin knockout mice

“…The recovery period from the carotid denervation was at least 4 days before the measurements of HR and MAP. The success of the denervation was confirmed by the increased fluctuation in MAP and no HR response to the fluctuation as in Table 1 (4).…”

Spontaneous baroreflex control of heart rate versus cardiac output: altered coupling in heart failure

“…Several previous studies have examined spontaneous baroreflex control of HR during rapid, transient changes in blood pressure under various experimental and pathological conditions (1,3,11,13,18,21,25,32). However, whether the spontaneous baroreflex HR responses functionally translate into effective blood pressure regulation has often been uncertain, since the extent to which HR responses cause changes in CO can be variable.…”

“…Changes in arterial blood pressure result in arterial baroreflex-mediated reciprocal changes in heart rate (HR) and total peripheral resistance. Arterial baroreflex sensitivity (cardiac component) has often been assessed via techniques that analyze normally occurring spontaneous changes in blood pressure and the reciprocal changes in HR (3,12,21,32). This technique has been used as an index of cardiac baroreflex function in a number of species, including humans, and in many experimental and pathological conditions (1,3,11,13,18,21,25,32).…”

“…Arterial baroreflex sensitivity (cardiac component) has often been assessed via techniques that analyze normally occurring spontaneous changes in blood pressure and the reciprocal changes in HR (3,12,21,32). This technique has been used as an index of cardiac baroreflex function in a number of species, including humans, and in many experimental and pathological conditions (1,3,11,13,18,21,25,32). Sinoaortic baroreflex denervation virtually abolishes baroreflex sensitivity assessed via this method, indicating that the spontaneous reciprocal changes in HR that occur as a result of changes in arterial pressure are indeed mediated by the baroreflex (1,19).…”

Efeitos sequenciais do treinamento aeróbio sobre o sistema renina-angiotensina em núcleos autonômicos de ratos normotensos e hipertensos.

“…Dentre os ajustes cardiovasculares benéficos que condicionam a queda da PA em hipertensos, citam-se: 1) redução da freqüência e/ou débito cardíaco, associados ao remodelamento do coração (CLAUSEN, 1977;TIPTON et al, 1999;VÉRAS-SILVA et al, 1997); 2) redução da resistência vascular periférica associada à redução da razão parede/luz de arteríolas e à redução da resistência (MIKINES et al, 1989); 6) alteração do balanço autonômico, com redução do tônus simpático e facilitação do tônus vagal (BURGER et al, 1998;DI CARLO;BISHOP, 1992;GRASSI et al, 1994;MICHELINI, 2007a). Mesmo nos indivíduos normotensos, em que o treinamento aeróbio não é acompanhado de queda da PA, há uma importante alteração no balanço autonômico ao coração e vasos, acompanhada de angiogênese em músculos exercitados (AMARAL et al, 2000(AMARAL et al, , 2001COIMBRA et al, 2008;FRANÇA;MICHELINI, 2001 Estes ajustes, por facilitarem o funcionamento das alças bulbar e suprabulbar, melhoram o controle autonômico da circulação, facilitando a redução da FC basal (em normotensos e hipertensos treinados) e a redução da atividade simpática periférica e a queda da PA (em hipertensos treinados).…”