Articles: pressoreceptors-physiology.
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Carotid sinus baroreceptor (CBR) sensitivity may be increased by electrical stimulation of sympathetic nerves passing to the carotid sinus region. It remains unknown if reflexly induced changes in efferent sympathetic discharge affect CBR function. In 17 anesthetized dogs, we reflexly induced alterations in sympathetic discharge and recorded CBR activity originating from a vascularly isolated carotid sinus. ⋯ Raising pressure (to 200 mmHg) in the contralateral carotid sinus (n = 7) resulted in a reflex decrease in arterial pressure (169 +/- 16 to 129 +/- 13 mmHg) and a reduction (82 +/- 3% of control) in baroreceptor activity (P less than 0.05). The changes in baroreceptor discharge were abolished by ipsilateral cervical sympathectomy or ganglionic blockade (n = 4). Our findings demonstrate that reflexly induced alterations in the activity of sympathetic fibers innervating the carotid sinuses can modulate baroreceptor discharge.
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The Journal of physiology · Sep 1982
Comparative StudyReflex response of the rabbit hind-limb muscle vascular bed to baroreceptor stimulation and its modification by pregnancy.
1. The pressure--flow relationship of the blood-perfused skinned hind limb has been compared in primigravid pregnant and virgin non-pregnant rabbits while pressure within the vascularly isolated carotid sinus was held at a series of non-pulsatile values. 2. At each level of sinus pressure the slope of the pressure--flow relationship was steeper in the pregnant animals. ⋯ There seemed to be a small reduction in the range and gain of the reflex in the pregnant group but this was not statistically significant. 5. We have previously shown total peripheral resistance in the pregnant rabbit to be less than that in the non-pregnant rabbit at the same level of sinus pressure. The lower hind-limb vascular resistance of the pregnant rabbit at any given sinus pressure must contribute to this reduced total peripheral resistance.
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Acta Physiol. Scand. · Oct 1979
Influence of intravenous infusion on heart rate, sympathetic and vagal efferentation and left atrial and aortic baroreceptor activity in dogs.
The influence of 42 i.v. infusions of saline on heart rate, sympathetic and vagal cardiac efferent activity and on the aortic baroreceptor and left atrial B-type nerve impulse activity was studied in 32 morphine-chloralose anesthetized dogs. The responses in heart rate were tachycardic in 31 infusions and bradycardic in 11 infusions. In tachycardia, sympathetic activity increased in a majority of the cases but also decreases and nonsignificant changes were observed. ⋯ The aortic baroreceptor and left atrial B-type receptor activity rate increased both in tachycardia and bradycardia. Changes in the activities of these receptors do not explain the different heart rate responses. It is supposed that bradycardic responses result from changes in cardiac contraction associated with some reflex mechanism suppressing the excitatory influence of the activity of atrial receptors on sympathetic cardiac efferentation.
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Circulation research · Oct 1975
Influence of cardiopulmonary vagal afferent activity on carotid chemoreceptor and baroreceptor reflexes in the dog.
The goal of this study was to determine if physiological levels of cardiopulmonary vagal afferent activity modulate carotid chemoreceptor and baroreceptor reflexes. In anesthetized, ventilated dogs, the aortic nerves and the cervical sympathetic trunks were cut, and atropine was administered so that vagotomy would interrupt only cardiopulmonary afferent impulses. Reflex vascular responses were observed in perfused gracilis muscle and hindpaw. ⋯ The results indicate that interruption of cardiopulmonary afferents potentiates the vascular and ventilatory responses to activation of the carotid chemoreceptors and augments the gain of the carotid baroreceptor reflex at low carotid pressures. These findings suggest that physiological levels of cardiopulmonary vagal afferent impulses suppress carotid baroreceptor and chemoreceptor reflexes through an interaction in the central nervous system. The suppressive effect on the chemoreceptor reflex may be distinct from tonic restraint of the vasomotor center by vagal afferents, since it involves sympathetic vasodilator as well as vasoconstrictor responses and may occur without suppression of base-line adrenergic constrictor tone.
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Circulation research · Aug 1975
Reduced baroreflex sensitivity with volume loading in conscious dogs.
The Bainbridge reflex, i.e., the effect of rapid saline infusion (1.1 +/- 0.1 liters) on heart rate and arterial and atrial blood pressures, was examined in 12 intact conscious dogs; mean arterial blood pressure rose by 33 +/- 3 (SE) mm Hg, mean atrial pressure by 14 +/- 1 mm Hg, and heart rate by 75 +/- 9 beats/min. After beta-receptor blockade, heart rate rose slightly less (+49 +/- 5 beats/min, P = 0.05). Cholinergic blockade, combined cholinergic and beta-receptor, or beta-receptor blockade after vagotomy blocked the heart rate response to the infusion. ⋯ After a mild amount of volume loading, when atrial pressure was 8 +/- 2 mm Hg, the PI/SAP slope was significantly depressed from normal. When atrial pressure was elevated further to 28 +/- 1 mm Hg by volume loading, the slope was further depressed. Thus, arterial baroreflex sensitivity is reduced progressively as atrial pressure is raised by volume loading, an observation that explains how heart rate can rise strikingly in the face of an elevated arterial blood pressure.