Participation of cardiac and peripheral sympathetics in carotid occlusion response

Physiological Sympathetic Activation Reduces Systemic Inflammation: Role of Baroreflex and Chemoreflex

Baroreflex and chemoreflex act through the autonomic nervous system, which is involved with the neural regulation of inflammation. The present study reports the effects of reflex physiological sympathetic activation in endotoxemic rats using bilateral carotid occlusion (BCO), a physiological approach involving the baroreflex and chemoreflex mechanisms and the influence of the baroreceptors and peripheral chemoreceptors in the cardiovascular and systemic inflammatory responses. After lipopolysaccharide (LPS) administration, the arterial pressure was recorded during 360 min in unanesthetized rats, and serial blood samples were collected to analyze the plasma cytokine levels. BCO elicited the reflex activation of the sympathetic nervous system, providing the following outcomes: (I) increased the power of the low-frequency band in the spectrum of the systolic arterial pressure during the BCO period; (II) reduced the levels of pro-inflammatory cytokines in plasma, including the tumor necrosis factor (TNF) and the interleukin (IL)-1β; (III) increased the plasma levels of anti-inflammatory cytokine IL-10, 90 min after LPS administration. Moreover, selective baroreceptor or chemoreceptor denervation deactivated mechanosensitive and chemical sensors, respectively, and decreased the release of the LPS-induced cytokine but did not alter the BCO modulatory effects. These results show, for the first time, that physiological reflex activation of the sympathetic circuit decreases the inflammatory response in endotoxemic rats and suggest a novel function for the baroreceptors as immunosensors during the systemic inflammation.

A population model of integrative cardiovascular physiology

We present a small integrative model of human cardiovascular physiology. The model is population-based; rather than using best fit parameter values, we used a variant of the Metropolis algorithm to produce distributions for the parameters most associated with model sensitivity. The population is built by sampling from these distributions to create the model coefficients. The resulting models were then subjected to a hemorrhage. The population was separated into those that lost less than 15 mmHg arterial pressure (compensators), and those that lost more (decompensators). The populations were parametrically analyzed to determine baseline conditions correlating with compensation and decompensation. Analysis included single variable correlation, graphical time series analysis, and support vector machine (SVM) classification. Most variables were seen to correlate with propensity for circulatory collapse, but not sufficiently to effect reasonable classification by any single variable. Time series analysis indicated a single significant measure, the stressed blood volume, as predicting collapse in situ, but measurement of this quantity is clinically impossible. SVM uncovered a collection of variables and parameters that, when taken together, provided useful rubrics for classification. Due to the probabilistic origins of the method, multiple classifications were attempted, resulting in an average of 3.5 variables necessary to construct classification. The most common variables used were systemic compliance, baseline baroreceptor signal strength and total peripheral resistance, providing predictive ability exceeding 90%. The methods presented are suitable for use in any deterministic mathematical model.

Baroreceptor and chemoreceptor contributions to the hypertensive response to bilateral carotid occlusion in conscious mice

This study aimed to characterize the role played by baroreceptors and chemoreceptors in the hypertensive response to bilateral carotid occlusion (BCO) in conscious C57BL mice. On the day before the experiments the animals were implanted with pneumatic cuffs around their common carotid arteries and a femoral catheter for measurement of arterial pressure. Under the same surgical approach, groups of mice were submitted to aortic or carotid sinus denervation or sham surgery. BCO was performed for 30 or 60 s, promoting prompt and sustained increase in mean arterial pressure and fall in heart rate. Compared with intact mice, the hypertensive response to 30 s of BCO was enhanced in aortic-denervated mice (52 ± 4 vs. 41 ± 4 mmHg; P < 0.05) but attenuated in carotid sinus-denervated mice (15 ± 3 vs. 41 ± 4 mmHg; P < 0.05). Suppression of peripheral chemoreceptor activity by hyperoxia [arterial partial pressure of oxygen (Pa(O(2))) > 500 mmHg] attenuated the hypertensive response to BCO in intact mice (30 ± 6 vs. 51 ± 5 mmHg in normoxia; P < 0.05) and abolished the bradycardia. It did not affect the hypertensive response in carotid sinus-denervated mice (20 ± 4 vs. 18 ± 3 mmHg in normoxia; P < 0.05). The attenuation of the hypertensive response to BCO by carotid sinus denervation or hyperoxia indicates that the hypertensive response in conscious mice is mediated by both baro- and chemoreceptors. In addition, aortic denervation potentiates the hypertensive response elicited by BCO in conscious mice.

Permanent, bilateral common carotid artery occlusion in the rat: a model for chronic cerebral hypoperfusion-related neurodegenerative diseases

Chronic cerebral hypoperfusion has been associated with cognitive decline in aging and Alzheimer's disease. Moreover, the pattern of cerebral blood flow in mild cognitive impairment has emerged as a predictive marker for the progression into Alzheimer's disease. The reconstruction of a pathological condition in animal models is a suitable approach to the unraveling of causal relationships. For this reason, permanent, bilateral occlusion of the common carotid arteries (2VO) in rats has been established as a procedure to investigate the effects of chronic cerebral hypoperfusion on cognitive dysfunction and neurodegenerative processes. Over the years, the 2VO model has generated a large amount of data, revealing the 2VO-related pattern of cerebral hypoperfusion and metabolic changes, learning and memory disturbances, failure of neuronal signaling, and the neuropathological changes in the hippocampus. In addition, the model has been introduced in research into ischemic white matter injury and ischemic eye disease. The present survey sets out to provide a comprehensive summary of the achievements made with the 2VO model, and a critical evaluation and integration of the various results, and to relate the experimental data to human diseases. The data that have accumulated from use of the 2VO model in the rat permit an understanding of the causative role played by cerebral hypoperfusion in neurodegenerative diseases. Thorough characterization of the model suggests that 2VO in the rat is suitable for the development of potentially neuroprotective strategies in neurodegenerative diseases.

Pressure response to carotid occlusion in diabetic rats: effect of insulin therapy

Bilateral carotid occlusion (BCO) in conscious rats has been used as a maneuver to increase the sympathetic drive, producing a hypertensive response characterized by two components: an initial peak, and a maintained response of lower intensity. Acute (10-15 days) or chronic (6-13 weeks) diabetes was induced in Wistar rats with streptozotocin (STZ, 50 mg/kg, i.v.) while time-control rats received vehicle. Insulin (9 IU/kg, s.c.) was applied daily to other diabetic groups. Blood glucose was monitored three days after the administration of STZ and immediately before the experiment. Blood glucose was elevated in diabetic rats, but normal in time-control or diabetic rats treated with insulin. Basal mean arterial pressure (MAP) was reduced in diabetic as compared to time-control rats. The initial peak of the hypertensive response to BCO was blunted in either acute or chronic diabetic rats, whereas the maintained response was unaffected. Treatment of diabetic rats with insulin prevented the decrease in basal MAP and the attenuation of the initial peak caused by BCO. The maintained response was similar to that of time-control or non-treated rats. These findings suggest an abnormality of the carotid afference of the baroreflex caused by chronic hyperglycemia, which was prevented by treatment with insulin.

Neurohumoral mechanisms involved in the hypertensive response elicited by bilateral carotid occlusion in conscious intact or chronically sympathectomized rats

Bilateral carotid occlusion (BCO) increases the sympathetic drive to the circulatory system in conscious intact rats, producing a hypertensive response characterized by two components, i.e., an initial peak followed by a sustained response of lower intensity. The neurohumoral mechanisms involved in the hypertensive response to BCO were evaluated in conscious intact (INTACT) or chronic guanethidine sympathectomized (SYMPX) rats. To accomplish this, the receptor antagonists, prazosin for alpha1-adrenergic receptor, losartan for AT1 angiotensin II receptor and [d(CH2)5Tyr(Me)AVP] for vascular V1 vasopressin receptor were used. A saline control group was studied as well. Conscious rats were equipped with cuffs around the common carotid arteries plus arterial and venous catheters. The results indicate that the sympathetic nervous system is the main mechanism controlling the basal arterial pressure in conscious INTACT rats, whereas in chronically SYMPX rats the renin-angiotensin system plays this role. In INTACT rats prazosin abolished the initial peak and blunted the sustained hypertensive response due to BCO, while the other antagonists exhibited no effect. SYMPX rats did not present the initial peak but displayed an enhanced sustained response, which was blunted by prazosin or the vasopressin antagonist. In conclusion, activation of the sympathetic drive is responsible for both the initial peak and the sustained hypertensive response due to BCO in conscious INTACT rats. On the other hand, vasopressin acting in concert with the sympathetic nervous system, plays a key role in the potentiation of the sustained hypertensive response due to BCO in conscious chronically SYMPX rats.

Arterial baroreceptors and experimental diabetes

Alterations of the autonomic reflex control of the cardiovasclar system have been demonstrated in clinical and animal models of insulin-dependent diabetes mellitus. Established neuroaxonal dystrophy is considered the neuropathological hallmark of chronic experimental diabetes. However, the afferent arm of the arterial baroreflex, that is, the carotid sinus nerve and the aortic depressor nerve, has received much less attention in studies dealing with this physiopathological model. The attenuation of the pressure response to bilateral carotid occlusion in conscious rats indicates a derangement of the baroreflex, probably involving an alteration of the carotid sinus nerve. There is histological evidence obtained from adult spontaneous insulin-dependent diabetic rats (strain BB/S) of a carotid sinus nerve with signs of axonal swelling and intramyelinic edema, suggesting diabetic neuropathy. The study of aortic baroreceptor activity in anesthetized rats with short- and long-term streptozotocin diabetes by means of cross-spectral analysis of baroreceptor activity versus arterial pressure revealed a dysfunction in the afferent arm of the baroreflex even during a short period of diabetes. The morphology of the aortic depressor nerve of streptozotocin-diabetic rats indicated axonal atrophy by visual analysis remarkably at the distal segments of the nerves. This finding was confirmed by morphometric study of the myelinated fibers. In conclusion, although studies of the arterial baroreceptors related to experimental diabetes are scanty in the literature, there is electrophysiological and histological evidence demonstrating that the carotid sinus and the aortic depressor nerves are abnormal in this experimental model.

Dynamic effects of carotid sinus baroreflex on ventriculoarterial coupling studied in anesthetized dogs

We evaluated dynamic effects of the carotid sinus baroreflex on ventriculoarterial coupling. In seven anesthetized, vagotomized dogs, we bilaterally isolated carotid sinuses and randomly changed carotid sinus pressure while measuring aortic pressure, aortic flow, and left ventricular pressure. Estimating left ventricular end-systolic elastance (Ees) and effective arterial elastance (Ea) on a beat-to-beat basis, we determined transfer functions from the carotid sinus pressure to Ees (HEes) and from the carotid sinus pressure to Ea (HEa) over the frequency range spanning 0.002-0.25 Hz. Both HEes and HEa exhibited characteristics of a second-order low-pass filter. The gains of HEes and HEa were 0.085 +/- 0.065 (mean +/- SD) and 0.081 +/- 0.049 mm Hg/ml/mm Hg, respectively. There were no significant differences in natural frequencies (0.039 +/- 0.013 versus 0.039 +/- 0.007 Hz) or damping ratios (0.65 +/- 0.11 versus 0.64 +/- 0.24). The results indicated that the carotid sinus baroreflex dynamically altered Ees and Ea to the same extent in the process of stabilizing arterial pressure. Because the arterial system extracts maximal external work from a given heart when Ea equals Ees, the carotid sinus baroreflex appeared to be designed to regulate the ventricular and arterial properties to optimize the energy transmission from the left ventricle to the arterial system in anesthetized, vagotomized dogs.

Pressure-flow relationships of the canine iliac periphery and systemic hemodynamics: effects of sodiumnitroprusside and adenosine

It has been reported that sodiumnitroprusside (SNP) decreases mean systemic pressure and simultaneously increases pressure pulse amplification towards the iliac periphery (Kenner and van Zwieten 1982). This unexpected finding was suggested to be due to a decrease in iliac peripheral resistance but an increase in iliac differential resistance. In order to investigate this apparent contradiction, the iliac periphery was hemodynamically isolated from the rest of the circulation and perfused with the dog's own blood by means of a pump. Perfusion pressure (P) and flow (F), femoral venous pressure (Pv), systemic pressure (Ps) and cardiac output (CO) were measured. Steady state pressure-flow relations of the isolated bed were obtained during control and during various i.v. infusion rates of SNP and adenosine (ADS) and were found to be straight (mean r = 0.99). Their slope (delta P/delta F) was defined as differential resistance (Rd). Peripheral resistance (Rp) of the iliac bed was defined as Rp = (P-Pv)/F, calculated at the flow value where perfusion pressure equalled the prevailing systemic pressure. Total peripheral resistance (TPR) was defined as TPR = Ps/CO. The changes of Rd, Rp, Ps, CO and TPR with respect to control show that during low SNP infusion rates Rd and Rp were both increased while TPR was decreased. During all infusion rates of SNP CO did not change while Ps decreased. During low infusion rates of adenosine CO increased while Ps, Rd and Rp did not change and TPR decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of unilateral and bilateral carotid artery ligation in the spontaneously hypertensive rat

Male and female, spontaneously hypertensive rats (SHR) with blood pressures ranging from 190-210 mmHg were subjected unilateral or bilateral carotid artery ligation. Representative numbers of animals were killed 2, 4, 6, 8, 10, 12, 24 and 48 hours later. Severe cerebral ischemia caused a significant and protracted increase in the pre-existent high blood pressure, the enzymes CPK, SGOT and LDH triglycerides, free fatty acids, glucose, and corticosterone. Despite these marked pathophysiologic changes, the brains of these animals were free of real damage except for cerebral edema and scattered petechiae. Some of the animals developed massive atrial thrombi and myocardial infarcts. It is suggested that severe cerebral ischemia precipitated the myocardial infarcts through the aegis of the hypothalamic-pituitary-adrenal stress response.

Extent of carotid sinus regulation of the myocardial contractile state in conscious dogs

The effects of bilateral carotid artery occlusion (BCO) and carotid sinus nerve stimulation (CSNS) on left ventricular (LV) pressure (P), diameter (D), velocity of contraction (V), rate of change of pressure (dP/dt), and cardiac output were studied in conscious dogs instrumented with ultrasonic diameter gauges, miniature pressure gauges, and aortic electromagnetic flow transducers. The effects of BCO and CSNS were also studied after automatic blockade and were compared to similar alterations in pressure produced by norepinephrine, methoxamine, and nitroglycerin. When heart rate was maintained constant with atrial stimulation, BCO had little effect on ventricular contractility, increasing isolength systolic pressure (LV P(iso)) by 36% while isolength velocity of myocardial shortening (V(iso)) decreased by 12% and (dP/dt)/P fell by 8%. These effects could be explained largely by vasoconstriction, since elevating systolic pressure with methoxamine produced similar results, while norepinephrine increased V(iso) by 36% and (dP/dt)/P by 56%. CSNS produced directionally opposite results from BCO; it decreased P(iso) by 15%, V(iso) increased by 11%, while (dP/dt)/P remained almost constant. These effects may be explained largely by vasodilatation since reducing systolic pressure to the same level with nitroglycerin produced similar results. When peripheral vasoconstriction was minimized by phenoxybenzamine pretreatment. BCO produced a slight positive inotropic effect (P(iso) increased by 8%, V(iso) by 4%, and (dp/dt)/P by 10%), while CSNS produced a slight negative inotropic effect (P(iso) decreased by 3%, V(iso) decreased by 5%, and (dP/dt)/P by 7%).Thus, in the normal, healthy, conscious dog, the carotid sinuses exert relatively little control of the inotropic state of the left ventricle; moreover, this small inotropic action is masked by the more powerful effects on peripheral resistance.