Cardiac receptors: their function in health and disease

Interoceptive signals from the heart and coronary circulation in health and disease

This review considers interoceptive signalling from the heart and coronary circulation. Vagal and cardiac sympathetic afferent sensory nerve endings are distributed throughout the atria, ventricles (mainly left), and coronary artery. A small proportion of cardiac receptors attached to thick myelinated vagal afferents are tonically active during the cardiac cycle. Dependent upon location, these mechanoreceptors detect fluctuations in atrial volume and coronary arterial perfusion. Atrial volume and coronary arterial signals contribute to beat-to-beat feedback control and physiological homeostasis. Most cardiac receptors are attached to thinly myelinated or nonmyelinated C fibres, many of which are unresponsive to the cardiac cycle. Of these, there are many chemically sensitive cardiac receptors which are activated during myocardial stress by locally released endogenous substances. In contrast, some tonically inactive receptors become activated by irregular ventricular wall mechanics or by distortion of the ischaemic myocardium. Furthermore, some are excited both by chemical mediators of ischaemia and wall abnormalities. Reflex responses arising from cardiac receptors attached to thinly myelinated or nonmyelinated are complex. Impulses that project centrally through vagal afferents elicit sympathoinhibition and hypotension, whereas impulses travelling in cardiac sympathetic afferents and spinal pathways elicit sympathoexcitation and hypertension. Two opposing cardiac reflexes may provide a mechanism for fine-tuning a composite haemodynamic response during myocardial stress. Sympathetic afferents provide the primary pathway for transmission of cardiac nociception to the central nervous system. However, activation of sympathetic afferents may increase susceptibility to life-threatening arrhythmias. Notably, the cardiac sympathetic afferent reflex predominates in pathophysiological states including hypertension and heart failure.

Closed-Loop Vagus Nerve Stimulation for the Treatment of Cardiovascular Diseases: State of the Art and Future Directions

The autonomic nervous system exerts a fine beat-to-beat regulation of cardiovascular functions and is consequently involved in the onset and progression of many cardiovascular diseases (CVDs). Selective neuromodulation of the brain-heart axis with advanced neurotechnologies is an emerging approach to corroborate CVDs treatment when classical pharmacological agents show limited effectiveness. The vagus nerve is a major component of the cardiac neuroaxis, and vagus nerve stimulation (VNS) is a promising application to restore autonomic function under various pathological conditions. VNS has led to encouraging results in animal models of CVDs, but its translation to clinical practice has not been equally successful, calling for more investigation to optimize this technique. Herein we reviewed the state of the art of VNS for CVDs and discuss avenues for therapeutic optimization. Firstly, we provided a succinct description of cardiac vagal innervation anatomy and physiology and principles of VNS. Then, we examined the main clinical applications of VNS in CVDs and the related open challenges. Finally, we presented preclinical studies that aim at overcoming VNS limitations through optimization of anatomical targets, development of novel neural interface technologies, and design of efficient VNS closed-loop protocols.

Venoconstrictor responses to activation of bradykinin-sensitive pericardial afferents involve the region of the hypothalamic paraventricular nucleus

Veins are important in the control of venous return, cardiac output, and cardiovascular homeostasis. However, the effector systems modulating venous function remain to be fully elucidated. We demonstrated that activation of bradykinin-sensitive pericardial afferents elicited systemic venoconstriction. The hypothalamic paraventricular nucleus (PVN) is an important site modulating autonomic outflow to the venous compartment. We tested the hypothesis that the PVN region is involved in the venoconstrictor response to pericardial injection of bradykinin. Rats were anesthetized with urethane/alpha chloralose and instrumented for recording arterial pressure, vena caval pressure, and mean circulatory filling pressure (MCFP), an index of venous tone. The rats were fitted with a pericardial catheter and PVN injector guide tubes. Mean arterial pressure (MAP), heart rate (HR), and MCFP responses to pericardial injection of bradykinin (1, 10 µg/kg) were recorded before and after PVN injection of omega conotoxin GVIA (200 ng/200 nl). Pericardial injection of saline produced no systematic effects on MAP, HR, or MCFP. In contrast, pericardial injection of bradykinin was associated with short latency increases in MAP (16 ± 4 to 18 ± 2 mm Hg) and MCFP 0.35 ± 0.19 to 1.01 ± 0.27 mm Hg. Heart rate responses to pericardial BK were highly variable, but HR was significantly increased (15 ± 9 bpm) at the higher BK dose. Conotoxin injection in the PVN region did not affect baseline values for these variables. However, injection of conotoxin into the area of the PVN largely attenuated the pressor (-1 ± 3 to 6 ± 3 mm Hg), MCFP (-0.19 ± 0.07 to 0.20 ± 0.18 mm Hg), and HR (4 ± 14 bpm) responses to pericardial bradykinin injection. We conclude that the PVN region is involved in the venoconstrictor responses to pericardial bradykinin injection.

Hemodynamic patterns associated with activation of bradykinin-sensitive pericardial afferents

The heart is endowed with reflexogenic areas capable of powerful blood pressure responses. Relatively little work has studied the hemodynamic mechanisms underlying these responses and whether these are sexually dimorphic. We hypothesized that activation of bradykinin-sensitive pericardial afferents would produce a sexually dimorphic cardiac output response. Male and female Sprague Dawley rats were anesthetized and instrumented with catheters for recording arterial pressure, with an aortic arch flow probe to record cardiac output and with a catheter in the pericardial sac. Mean arterial pressure (MAP), cardiac index (CI) and total peripheral resistance index (TPRI) responses to pericardial bradykinin injection (0.1, 1 μg/kg) were recorded. Pericardial bradykinin injection caused similar increases in MAP in male and female rats. However, the underlying hemodynamic patterns varied considerably. We identified a cluster of CI responders and TPRI responders in both male and female rats. Within CI responders, females exhibited greater CI increases than males. Conversely, in TPRI responders, males exhibited a greater TPRI increase than females. We conclude that aggregate activation of bradykinin-sensitive pericardial afferents is associated with a relatively uniform pressor response but different hemodynamic patterns with males exhibiting a more robust vascular response and females a more robust cardiac output response.

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Mixed cardiac afferent activation caused similar pressor responses in male and female rats.

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Subsets of cardiac output and vascular resistance responders were identified.

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Cardiac output responses were greater in female rats.

Physiology of Human Hemorrhage and Compensation

Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.

Activation of bradykinin-sensitive pericardial afferents increases systemic venous tone in conscious rats

Our understanding of reflex regulation of veins lags behind that of the arterial system. While the cardiac sympathetic afferent reflex (CSAR) exerts control over sympathetic outflow, its effect on venous tone is not known. We tested the hypothesis that activation of pericardial bradykinin sensitive afferents elicits systemic venoconstriction. Male and female Sprague Dawley rats were chronically instrumented for measurement of arterial pressure and mean circulatory filling pressure, an index of venous tone, and with an indwelling pericardial catheter. Mean arterial pressure, heart rate and mean circulatory filling pressure responses were assessed in conscious rats in response to graded pericardial injections of bradykinin (1.5-20 μg/kg) before and after ganglionic blockade, and to intravenous norepinephrine (0.05-0.8 μg/kg). Bradykinin B2 receptor was assessed by Western blot. Pericardial bradykinin injections caused graded increases in mean arterial pressure, heart rate and mean circulatory filling pressure. These responses were markedly attenuated after autonomic blockade. The increments in mean circulatory filling pressure were attenuated in female rats. There were no differences in the venoconstrictor responses to norepinephrine or ventricular bradykinin receptor expression between male and females. We interpret these findings to indicate that activation of bradykinin sensitive pericardial afferents elicits a sexually dimorphic, autonomically mediated systemic venoconstrictor response. Differences in venous smooth muscle responses to norepinephrine or ventricular bradykinin receptor expression do not account for the sexual dimorphism. We conclude that systemic venoconstriction contributes to the overall hemodynamic response to activation of the cardiac sympathetic afferent reflex and that this effect is sexually dimorphic.

Roles of arterial baroreceptor reflex during bezold-jarisch reflex

Among the many cardiopulmonary reflexes, this review specifically examines the roles of the arterial baroreflex during the Bezold-Jarisch reflex (BJR). Activation of cardiopulmonary vagal afferent C-fibers induces hypotension, bradycardia, and apnea, which are known collectively as the BJR; myocardial ischemia and infarction might induce the BJR. Arterial baroreflex has been established as an important negative feedback system that stabilizes arterial blood pressure against exogenous pressure perturbations. Therefore, understanding the functions of the arterial baroreflex during the BJR is crucial for elucidating its pathophysiological implications. The main central pathways of the BJR and the baroreflex are outlined herein, particularly addressing the common pathway between the reflexes. Furthermore, the pathophysiological roles of the arterial baroreflex during the BJR are described along with a brief discussion of pathophysiological merits and shortcomings of the reflexes.

The mechanism of the negative chronotropic and dromotropic actions of adenosine 5'-triphosphate in the heart: an update

Adenosine 5'-triphosphate (ATP) plays a critical role in intracellular metabolism and energetics. Extracellular ATP is rapidly degraded to adenosine by ectoenzymes. Both ATP and adenosine suppress cardiac pacemakers' automaticity and atrioventricular nodal conduction, albeit via the different mechanism of actions. This historical update summarizes the current knowledge regarding the negative chronotropic and dromotropic actions of ATP and discusses the clinical implications regarding the utility of ATP as a diagnostic and therapeutic agent in the management of neutrally mediated syncope and paroxysmal supra ventricular tachycardia.

An essay on the circulation as behavior

Most conceptual models of the organization of the cardiovascular system begin with the premise that the nervous system regulates the metabolic and nonmetabolic reflex adjustments of the circulation. These models assume that all the neurally mediated responses of the circulation are reactive, i.e., reflexes elicited by adequate stimuli. This target article suggests that the responses of the circulation are conditional in three senses. First, as Sherrington argued, reflexes are conditional in that they never operate in a vacuum but in a context together with other reflexes. Guided by functional utility, they interact rather than add. Second, as Pavlov argued, stimuli acquire meanings as a result of experience. This notion of stimulus effect plus the Sherringtonian notion of conditionality suggest that association is one of the ways stimuli eliciting cardiovascular reflexes acquire their meanings and thus their relative strengths. Finally, as Skinner and others have argued, operants are responses that act upon the environment to obtain consequences – that is, stimuli. As operants, cardiovascular responses fulfill a major biological need, functioning proactively. The cardiovascular response is an integral component of the animal's behavior regardless of whether it is an elicited reflex or the eliciting stimulus acquired its properties as a result of the genetic inheritance of the animal or through experience, or the cardiovascular response is emitted in anticipation of an environmental consequence. The main theses of this essay are: (1) behavior is an integrated set of responses and the circulation is one of the response systems comprising behavior; (2) behavior is, in part, determined by its functional significance within a context; (3) the contextual factors operative at the time of the behavior have a major role in determining which of the set of possible responses will determine the final act, that is, which behavior will be the effective response and which other behaviors will be concomitants.

Control of cardiac contractility in the rat working heart-brainstem preparation

A great deal of knowledge exists regarding neural control of myocardial function in the rat. Most of the studies addressing this issue were conducted either under general anaesthesia or in isolated hearts in vitro. Our principal aim was to provide a detailed quantitative description of mechanisms controlling cardiac contractility in the rat, in an anaesthetic-free preparation with a preserved functional brainstem. Furthermore, while vagally mediated negative inotropy is a well-known phenomenon, at present there is no direct evidence for its presence in the rat; we searched for such evidence. To this end, in the arterially perfused working heart-brainstem preparation of the rat, we measured left ventricular pressure (LVP) and computed its first derivative (LVdP/dt). We made the following new observations. (i) Zatebradine (cardiac sodium pacemaker current blocker) caused a bradycardia associated with increases in LVP and LVdP/dt; the latter effect was via a frequency-dependent mechanism. (ii) We confirmed that in the rat, the force-frequency relationship (dependence of contractility on heart rate) is positive over a low range of heart rates, and negative and linear at physiological levels of heart rate, and provided its quantitative description. (iii) The increase in systemic pressure caused a rise in contractility, and vagal blockade or destruction of the central nervous system did not alter this inotropic effect, suggesting that it was mediated by intrinsic cardiac mechanisms. (iv) Vagal stimulation caused complex polyphasic changes in LVdP/dt and LVP in unpaced preparations; during pacing, it caused slowly developing falls in LVdP/dt that could be prevented by atropine. We conclude that control of ventricular contractility in the rat heart differs from that in other mammals not only by its negative frequency dependence, but also in the potent influence of aortic pressure on LVdP/dt. At the level of autonomic neural control, our newly found, vagally mediated negative inotropic effect adds to the accumulating body of data regarding both the presence and the functional importance of parasympathetic innervation of the ventricular myocardium.

Cardiac autonomic neural remodeling and susceptibility to sudden cardiac death: effect of endurance exercise training

Sudden cardiac death resulting from ventricular tachyarrhythmias remains the leading cause of death in industrially developed countries, accounting for between 300,000 and 500,000 deaths each year in the United States. Yet, despite the enormity of this problem, both the identification of factors contributing to ventricular fibrillation as well as the development of safe and effective antiarrhythmic agents remain elusive. Subnormal cardiac parasympathetic regulation coupled with an elevated cardiac sympathetic activation may allow for the formation of malignant ventricular arrhythmias. In particular, myocardial infarction can reduce cardiac parasympathetic regulation and alter beta-adrenoceptor subtype expression enhancing beta(2)-adrenoceptor sensitivity that can lead to intracellular calcium dysregulation and arrhythmias. As such, myocardial infarction can induce a remodeling of cardiac autonomic regulation that may be required to maintain cardiac pump function. If alterations in cardiac autonomic regulation play an important role in the genesis of life-threatening arrhythmias, then one would predict that interventions designed to either augment parasympathetic activity and/or reduce cardiac adrenergic activity would also protect against ventricular fibrillation. Recently, studies using a canine model of sudden death demonstrate that endurance exercise training (treadmill running) enhanced cardiac parasympathetic regulation (increased heart rate variability), restored a more normal beta-adrenoceptor balance (i.e., reduced beta(2)-adrenoceptor sensitivity and expression), and protected against ventricular fibrillation induced by acute myocardial ischemia. Thus exercise training may reverse the autonomic neural remodeling induced by myocardial infarction and thereby enhance the electrical stability of the heart in individuals shown to be at an increased risk for sudden cardiac death.

Regulation of cardiac afferent excitability in ischemia

The heart at the time of Sir William Harvey originally was thought to be an insensate organ. Today, however, we know that this organ is innervated by sensory nerves that course centrally though mixed nerve pathways that also contain parasympathetic or sympathetic motor nerves. Angina or cardiac pain is now well recognized as a pressure-like pain that occurs during myocardial ischemia when coronary artery blood flow is interrupted. Sympathetic (or spinal) afferent fibers that are either finely myelinated or unmyelinated are responsible for the transmission of information to the brain that ultimately allows the perception of angina as well as activation of the sympathetic nervous system, resulting in tachycardia, hypertension, and sometimes arrhythmias. Although early studies defined the importance of the vagal and sympathetic cardiac afferent systems in reflex autonomic control, until recently there has been little appreciation of the mechanisms of activation of the sensory endings. This review examines the role of a number of chemical mediators and their sources that are activated by the ischemic process. In this regard, patients with ischemic syndromes, particularly myocardial infarction and unstable angina, are known to have platelet activation, which leads to release of a number of chemical mediators, including serotonin, histamine, and thromboxane A(2), all of which stimulate ischemically sensitive cardiac spinal afferent endings in the ventricles through specific receptor-mediated processes. Furthermore, protons from lactic acid, bradykinin, and reactive oxygen species, especially hydroxyl radicals, individually and frequently in combination, stimulate these endings during ischemia. Cyclooxygenase products appear to sensitize the endings to the action of bradykinin and histamine. These studies of the chemical mechanisms of activation of cardiac sympathetic afferent endings during ischemia have the potential to provide targeted therapies that can modify the angina and the deleterious reflex responses that have the potential to exacerbate ischemia and myocardial cell death.

Viscerosomatic interaction induced by myocardial ischemia in conscious dogs

Studies tested the hypothesis that myocardial ischemia induces increased paraspinal muscular tone localized to the T2–T5 region that can be detected by palpatory means. This is consistent with theories of manual medicine suggesting that disturbances in visceral organ physiology can cause increases in skeletal muscle tone in specific muscle groups. Clinical studies in manual and traditional medicine suggest this phenomenon occurs during episodes of myocardial ischemia and may have diagnostic potential. However, there is little direct evidence of a cardiac-somatic mechanism to explain these findings. Chronically instrumented dogs [12 neurally intact and 3 following selective left ventricular (LV) sympathectomy] were examined before, during, and after myocardial ischemia. Circumflex blood flow (CBF), left ventricular contractile function, electromyographic (EMG) analysis, and blinded manual palpatory assessments (MPA) of tissue over the transverse spinal processes at segments T2–T5 and T11–T12 (control) were performed. Myocardial ischemia was associated with a decrease in myocardial contractile function and an increase in heart rate. MPA revealed increases in muscle tension and texture/firmness during ischemia in the T2–T5 segments on the left, but not on the right or in control segments. EMG demonstrated increased amplitude for the T4–T5 segments. After LV sympathectomy, MPA and EMG evidence of increased muscle tone were absent. In conclusion, myocardial ischemia is associated with significant increased paraspinal muscle tone localized to the left side T4–T5 myotomes in neurally intact dogs. LV sympathectomy eliminates the somatic response, suggesting that sympathetic neural traffic between the heart and somatic musculature may function as the mechanism for the interaction.

Exploration of P2X3 in the rat stellate ganglia after myocardial ischemia

ATP is implicated in peripheral pain signaling by actions on P2X receptors, especially P2X(3) receptor. Cardiac primary afferents running in the sympathetic nerves are considered to be essential pathways for transmission of cardiac nociception to the central nervous system. Because little is known about P2X(3) involvement in cardiac nociception, this study observed the difference in P2X(3) localization and expression in stellate ganglia (SG) from naive rats and in a pathological model of myocardial ischemic injury induced by repeated subcutaneous isoprenaline injections. Distribution of P2X(3) and morphometry of neurons in SG were investigated by immunohistochemistry, Western blotting, in situ hybridization (ISH) and by sterological study. Diffuse cytoplasmic P2X(3) immunolabelling was observed by light microsocopy. No nuclear labeling was detected. The intensity of P2X(3) labeling in the experimental myocardial ischemic injury group was increased in relation to that of the control group. Numerical densities of stellate ganglion neurons in the experimental group were higher than those of the control group. By Western blotting and ISH, the signals of P2X(3) protein and its mRNA in the myocardial ischemic group were higher than those of the control group. The P2X(3) labeling intensity and the numerical density in SG of the experimental myocardial ischemic injury group were enhanced, suggesting the involvement of P2X(3) receptor for the transmission of pain after myocardial ischemic injury.

The antiarrhythmic effects of ischaemic preconditioning in anaesthetized dogs are prevented by atropine; role of changes in baroreceptor reflex sensitivity

1. Dogs, anaesthetized with chloralose and urethane, were subjected to a 25 min occlusion of the left anterior descending coronary artery. This resulted in ventricular ectopic activity, a reduction in baroreflex sensitivity (BRS, measured following the intravenous administration of phenylephrine), elevations in the epicardial ST-segment and increases in the degree of inhomogeneity of electrical activation, both measured from the ischaemic region of the left ventricular wall. 2. These changes were markedly reduced when the 25 min occlusion was preceded, 20 min earlier, by a 5 min (preconditioning) occlusion of the same coronary artery (e.g. VF during ischaemia reduced from 40% in the controls to 0%; P<0.05; BRS increased from 1.22+/-0.23 pre-occlusion to 1.61+/-0.25 mmHg ms(-1) post-occlusion in preconditioned dogs; cf. 1.28+/-0.29 to 0.45+/-0.12 mmHg ms(-1) respectively in the controls, P<0.05). 3. These beneficial effects of preconditioning were prevented by the administration, 10 min prior to the 25 min coronary artery occlusion, of atropine (1 mg kg(-1) i.v. followed by a continuous infusion of 0.04 mg kg(-1) h(-1)). For example, VF during occlusion was increased from 0% in the preconditioned dogs to 40% (P<0.05) in the presence of atropine and BRS was again reduced during occlusion (from 1.75+/-0.29 to 0.30+/-0.08 mmHg ms(-1); P<0.05). 4. We conclude that preconditioning reduces arrhythmia severity during ischaemia by favourably modifying cardiac autonomic receptor mechanism through enhancing vagal influences.

Positive and negative feedback mechanisms in the neural regulation of cardiovascular function in healthy and spinal cord-injured humans

BACKGROUND

We tested the hypothesis that in humans, hypertension/tachycardia and hypotension/bradycardia nonbaroreflex sequences that occur within spontaneous arterial pressure (AP) and R-R interval fluctuations are an expression of positive feedback mechanisms neurally regulating the cardiovascular system.

METHODS AND RESULTS

We studied 15 spinal cord-injured (SCI) subjects (8 tetraplegics and 7 paraplegics) and 8 healthy subjects. The occurrence of nonbaroreflex (NBseq) and baroreflex (Bseq) sequences, ie, hypertension-bradycardia and hypotension-tachycardia sequences, was assessed during rest and head-up tilt (HUT). The ratio between Bseq and NBseq (B/NB ratio) was also calculated. In resting conditions, the occurrence of NBseq was significantly lower (P:<0.05) in tetraplegics (7.9+/-1.5) than in paraplegics (16.2+/-3.2) and normal subjects (19.0+/-3.5), whereas the occurrence of Bseq was not significantly different between the 3 groups (38.6+/-11.9 versus 45.4+/-6.0 versus 47.0+/-11.9). In tetraplegics, the B/NB ratio showed a marked, significant decrease (from 8.4+/-4.2 to 1.9+/-0.8, P:<0.05) in response to HUT, whereas in normal subjects, it showed a significant increase (from 3.5+/-0.7 to 9.4+/-2.7, P:<0.05). In paraplegics, the B/NB ratio did not change significantly in response to HUT (from 4.5+/-1.6 to 4.8+/-1.1).

CONCLUSIONS

Our data suggest that nonbaroreflex sequences occur in humans and might represent the expression of an integrated, neurally mediated, feed-forward type of short-term cardiovascular regulation that is able to interact dynamically with feedback mechanisms of baroreflex origin.

Correlation between symptomatology and site of acute myocardial infarction

OBJECTIVE

We determined the occurrence of presenting symptoms in patients with different sites of acute myocardial infarction after controlling for age and conventional risk factors.

METHODS

Hospital-based study of patients hospitalized because of first anterior (n=731), inferior (n=719) and lateral (n=96) infarction in Clinical Hospital Split between 1990 and 1994. Data form about presenting symptoms and clinical profile was completed for each patient.

RESULTS

Anterior infarctions were more often presented by headache (adjusted odds ratio (OR)=1.67, 95% CI=1.06-2.62), weakness (OR=1.60, 95% CI=1.31-1.96), dyspnea (OR=1.40, 95% CI=1.14-1.72), cough (OR=2.24, 95% CI=1.59-3.16), vertigo (OR=2.04, 95% CI=1.40-2.99) and tinnitus (OR=2.09, 95%CI=1.06-4.14). Inferior infarctions were more often associated with epigastric (OR=1.71, 95%CI=1.30-2.24), neck (OR=1.47, 95% CI=1.10-1.98) and jaw pain (OR=2.16, 95% CI=1.42-3.27), sweating (OR=1.56, 95% CI=1.27-1.92), nausea (OR=2.01, 95%CI=l.64-2.46), vomiting (OR=1.55, 95% CI=1.22-1.97), belching (OR=1.57, 95% CI=1.21-2.03) and hiccups (OR=2.88, 95%CI=1.53-5.42). Patients with lateral infarctions were more likely to complain of left arm (OR=1.80, 95% CI=1.07-3.05), left shoulder (OR=1.82, 95% CI=1.19-2.79) and back pain (OR=2.40, 95% CI=1.28-4.46). Pain was less frequently reported by hypercholesterolemic (P=l.4x10(-7)), patients over 70 years (P=0.002), women (P=0.0007) and those with non-triggered infarction (P=0.0009), whereas those over 70 (P=1.7x10(-6)) and men (P=0.0003) were less likely to report other relevant symptoms.

CONCLUSIONS

Our study suggests a linkage between different infarction sites and specific groups of symptoms. Furthermore, coronary patients should give their full attention to non-specific symptoms and any kind of discomfort.

Bronchovascular role in pulmonary congestion

1. A postulated role for the bronchial circulation in the development of pulmonary congestion may be based on recent studies of bronchovascular control. 2. The bronchial circulation is the nutrient blood supply of the conducting airways and, therefore, plays an important role in the function of the bronchial mucosa. Mucosal swelling secondary to elevation of mucosal capillary hydrostatic pressure may decrease airway calibre, increase resistance to airflow and precipitate symptoms of pulmonary congestion. 3. Resting mucosal capillary hydrostatic pressure is relatively constant due to autoregulation of bronchial blood flow and is maintained low by nett bronchovascular constriction due to the dominance of autonomic vasoconstriction over nitric oxidedependent vasodilatation. 4. Bronchial blood flow is also regulated by cardiac afferent reflexes. Stimulation of cardiac vagal and spinal afferents produces vasodilatation and vasoconstriction, respectively. Tonic activity of cardiac spinal afferents probably contributes to the resting autonomic vasoconstriction. 5. Therefore, mild heart failure, which is associated with abnormal cardiovascular reflex function, may decrease cardiac spinal afferent-mediated bronchial vasoconstriction and produce active dilatation due to stimulation of cardiac vagal afferents by excessive myocardial stretch, leading to bronchial mucosal swelling and pulmonary congestion.

Oxidative stress impairs cardiac chemoreflexes in diabetic rats

We investigated the effects of diabetes mellitus and antioxidant treatment on the sensory and reflex function of cardiac chemosensory nerves in rats. Diabetes was induced by streptozotocin (STZ; 85 mg/kg ip). Subgroups of sham- and STZ-treated rats were chronically treated with an antioxidant, vitamin E (60 mg/kg per os daily, started 2 days before STZ). Animals were studied 6-8 wk after STZ injection. We measured renal sympathetic nerve activity (RSNA), mean arterial blood pressure (MABP), and cardiac vagal and sympathetic afferent activities in response to stimulation of chemosensitive sensory nerves in the heart by epicardial application of capsaicin (Caps) and bradykinin (BK). In cardiac sympathetic-denervated rats, Caps and BK (1-10.0 microg) evoked a vagal afferent mediated reflex depression of RSNA and MABP, which was significantly blunted in STZ-treated rats (P < 0.05). In vagal-denervated rats, Caps and BK (1-10.0 microg) evoked a sympathetic afferent-mediated reflex elevation of RSNA and MABP, which also was significantly blunted in STZ-treated rats (P < 0.05). Chronic vitamin E treatment effectively prevented these cardiac chemoreflex defects in STZ-treated rats without altering resting blood glucose or hemodynamics. STZ-treated rats with insulin replacement did not exhibit impaired cardiac chemoreflexes. In afferent studies, Caps and BK (0.1 g-10.0 microg) increased cardiac vagal and sympathetic afferent nerve activity in a dose-dependent manner in sham-treated rats. These responses were significantly blunted in STZ-treated rats. Vitamin E prevented the impairment of afferent discharge to chemical stimulation in STZ rats. The following were concluded: STZ-induced, insulin-dependent diabetes in rats extensively impairs the sensory and reflex properties of cardiac chemosensitive nerve endings, and these disturbances can be prevented by chronic treatment with vitamin E. These results suggest that oxidative stress plays an important role in the neuropathy of this autonomic reflex in diabetes.

Endogenous bradykinin activates ischaemically sensitive cardiac visceral afferents through kinin B2 receptors in cats

1. Activity of ischaemically sensitive cardiac visceral afferents during myocardial ischaemia induces both angina and cardiovascular reflexes. Increased production of bradykinin (BK) and cyclo-oxygenase products (i.e. prostaglandins (PGs)) occurs during myocardial ischaemia. However, the role of these agents in activation of ischaemically sensitive cardiac afferents has not been established. The present study tested the hypothesis that BK produced during ischaemia activates cardiac afferents through kinin B2 receptors. 2. Single-unit activity of cardiac afferents innervating the left ventricle was recorded from the left thoracic sympathetic chain (T1-T4) of anaesthetized cats. Ischaemically sensitive cardiac afferents were identified according to their response to 5 min of myocardial ischaemia. The mechanism of BK in activation of ischaemically sensitive cardiac afferents was determined by injection of BK (1 microgram kg-1 i.a.), des-Arg9-BK (1 microgram kg-1 i.a., a specific kinin B1 receptor agonist), kinin B2 receptor antagonists: HOE140 (30 micrograms kg-1 i.v.) and NPC-17731 (40 micrograms kg-1 i.v., cyclo-oxygenase inhibition with indomethacin (5 mg kg-1 i.v.) and NPC-17731 (40 micrograms kg-1 i.v.) after pretreatment with indomethacin (5 mg kg-1 i.v.). 3. We observed that BK increased the discharge rate of all eleven ischaemically sensitive cardiac afferents from 0.39 +/- 0.12 to 1.47 +/- 0.37 impulses s-1 (P < 0.05). Conversely, des-Arg9-BK did not significantly increase the activity of eleven ischaemically sensitive fibres (0.58 +/- 0.02 vs. 0.50 +/- 0.18 impulses s-1. HOE140 significantly attenuated the response of twelve afferents to ischaemia (0.61 +/- 0.22 to 1.85 +/- 0.5 vs. 0.53 +/- 0.16 to 1.09 +/- 0.4 impulses s-1). NPC-17731, another kinin B2 receptor antagonist, had similar inhibitory effects on six other ischaemically sensitive cardiac afferents (0.35 +/- 0.14 to 1.19 +/- 0.29 vs. 0.22 +/- 0.08 to 0.23 +/- 0.07 impulses s-1). Indomethacin significantly reduced the responses of seven afferents to ischaemia (0.35 +/- 0.13 to 1.89 +/- 0.48 vs. 0.40 +/- 0.10 to 0.76 +/- 0.24 impulses s-1). Indomethacin also significantly reduced the responses of six ischaemically sensitive cardiac afferents to BK (2.65 +/ 1.23 to 1.2 +/- 0.51 impulses s-1. In six cats pretreated with indomethacin, NPC-17731 attenuated the impulse activity of six ischaemically sensitive cardiac afferents (0.39 +/- 0.12 to 1.0 +/- 0.3 vs. 0.26 +/- 0.14 to 0.48 +/- 0.20 impulses s-1. 4. This study demonstrates that BK produced during ischaemia contributes to stimulation of ischaemically sensitive cardiac visceral afferents through activation of kinin B2 receptors. Furthermore, BK stimulates ischaemically sensitive cardiac visceral afferents through a mechanism that is, at least in part, independent of cyclo-oxygenase activation.

Neurally mediated syncope: a review of cardiac and arterial receptors

This article reviews the basic physiology of the reflexogenic areas of the heart and the mechano- and baroreceptors that regulate cardiovascular and autonomic homeostasis, all of which contribute to our understanding of the pathogenesis of neurally mediated syncope. The mechanisms of neurally mediated syncope may involve excessive activation of ventricular receptors that trigger severe hypotension and bradycardia. Thus, neurally mediated syncope may be the clinical expression of the Bezold-Jarisch reflex, which occurs in situations of increased sympathetic activity, perhaps as a result of heightened cardiac receptor sensitivity. The arterial baroreceptors exert a ubiquitous influence on the heart and circulation, and serve primarily to buffer transient changes in arterial pressure by transmitting sensory information regarding their stretch to the central nervous system. This information, in conjunction with cardiac receptor input, elicits alterations in neural efferent output from sympathetic and parasympathetic fibers to provide subtle, continuous regulation of beat-to-beat cardiovascular hemodynamics to an array of physiologic and psychological stressors.

Comparison of postoperative emesis, recovery profile, and analgesia in pediatric strabismus repair. Rectal acetaminophen versus intravenous fentanyl-droperidol

BACKGROUND

Postoperative nausea and vomiting comprise significant morbidity in pediatric patients undergoing strabismus repair and can prolong hospitalization. Many authors recommend routine intraoperative opiate analgesia and prophylactic antiemetics.

METHODS

A prospective, comparative, randomized study to assess rectal acetaminophen (n = 45) to intravenous fentanyl-droperidol (n = 45) to resolve recovery profile, emesis rate, and adequacy of analgesia in a pediatric strabismus repair population was performed, with standardization of the anesthetic technique. Data on pharmacoeconomic cost-effectiveness analysis, willingness to pay, and willingness to repeat were elucidated.

RESULTS

Emesis rate in the acetaminophen group was 9%, and the fentanyl-droperidol group was 13% (not statistically significant). There was a statistically significant shorter wake-up time, time in postanesthesia recovery, time in ambulatory surgery unit, time to first verbal command, time to first oral intake, time to ambulation, and time to return to normal activity in the acetaminophen group (P < 0.05). Postoperative analgesic potency of rectal acetaminophen was adequate and equivalent by Observer Pain Scale. Parental satisfaction was similar by willingness-to-pay and willingness-to-repeat postoperative survey. Cost-effectiveness ratio (i.e., cost per treatment success) for acetaminophen and fentanyl-droperidol groups was $0.33 and $87.91, respectively.

CONCLUSIONS

Prophylactic fentanyl-droperidol prolongs the length-to-stay and recovery time and provides no discrete identifiable benefit over acetaminophen alone in this population. Cost-effectiveness analysis strongly favors use of acetaminophen over fentanyl-droperidol prophylaxis in children undergoing primary strabismus surgery.

Cardioinhibitory-vasodepressor response to head-up tilt without hypoxaemia or myocardial ischaemia

We evaluated whether hypoxaemia and/or myocardial ischaemia are of importance for development of the bradycardic hypotensive phase (cardioinhibitory-vasodepressor syncope) of central hypovolaemia. Arterial blood gas variables and a twelve-lead electrocardiogram (ECG) were followed during head-up tilt in seven men. During tilt, before presyncopal symptoms appeared, mean arterial pressure (MAP) increased (from 67 +/- 7 to 78 +/- 6 mmHg) (mean +/- SE) as did heart rate (HR) (61 +/- 4 to 99 +/- 8 beats min-1) and total peripheral resistance (TPR) (11 +/- 1 to 17 +/- 1 mmHg min l-1) (P < 0.01), while cardiac output (5.9 +/- 0.5 to 4.6 +/- 0.6 l min-1) and central venous pressure (CVP) (4.2 +/- 0.4 to 1.3 +/- 0.7 mmHg) decreased (P < 0.01). After 40 +/- 7 min of head-up tilt presyncopal symptoms appeared together with a decrease in MAP to 48 +/- 7 mmHg, HR to 71 +/- 11 beats min-1 and TPR to 9 +/- 2 mmHg min l-1 (P < 0.01). Arterial oxygen tension was not changed and there was no ST-segment depression of the ECG. The results indicate that during central hypovolaemia decreases in HR and TPR are elicited during normoxaemia and without electrocardiographic signs of myocardial ischaemia.

Digitalis and heart failure: does digitalis really produce beneficial effects through a positive inotropic action?

Although digitalis was introduced to medicine long ago, the drug is still extensively used in clinical practice today. Opinions on its mechanism of action have undergone much change in the course of time, and the way in which cardiovascular effects are produced is still not completely clear. Limitations and contraindications for the use of digitalis substances are reported, especially in the treatment of ischemic heart disease. Preliminary data regarding the effects of digitalis on the diastolic phase are unfavorable, although the relationship between digitalis and diastolic function ought to be studied in greater depth in various clinical conditions. In spite of many recent trials, the old question of the usefulness of digitalis in the chronic treatment of patients in sinus rhythm and heart failure is still debated. An important clinical benefit in the chronic use of digitalis appears restricted to a relatively small proportion of patients with severe congestive heart failure, while in the majority of chronically treated subjects the effects of the drug are scanty or insignificant. The beneficial effect of digitalis used chronically is essentially believed to be due to its positive inotropic action. Since the vagomimetic and the antiadrenergic effects of digitalis have been demonstrated to be independent from its inotropic action, they could be considered determinants of the clinical benefits of digitalis. These indirect effects may be useful in the control of the negative neuroendocrine response developing during congestive heart failure. Thus the statement that digitalis is essentially an inotropic agent seems restrictive; its definition should reflect the favorable effects obtained in some cases of congestive heart failure rather than its various and contrasting underlying mechanisms of action.

Cardiovascular reflexes from cardiac sensory receptors

The mammalian heart, especially its left ventricle, is densely innervated by sensory nerves. One set of these travels to the brainstem in the vagus nerves; the other to the spinal cord in sympathetic nerves. Excitation of vagal cardiac afferents, especially unmyelinated afferents from the left ventricle, cause a reflex bradycardia and fall in blood pressure and, under some conditions, a massive release of AVP. The sympathetic afferents convey the sensation of cardiac pain, but innocuous stimuli may cause a reflex tachycardia and rise in blood pressure. Both sympathetic and vagal cardiac afferents can be excited by mechanical distension of the heart (mechanoreceptors), and by a variety of foreign and endogenous chemical substances (chemosensitive receptors). It is not yet clear whether the effective natural stimulus to these receptors is mechanical, or through the chemical products of myocardial metabolism. Neither is it clear whether information from the heart exerts a minute-to-minute regulatory effect on the circulation, or whether it has a purely defensive role in the face of extreme disturbances of cardiac function. Cardiogenic reflexes are also thought to be the cause of haemodynamic and humoral disturbances that occur in clinical conditions such as myocardial ischaemia or infarction, left ventricular outflow obstruction, and acute reduction in central blood volume as well as during coronary angiography.

Effects of exogenous adenosine in a patient with transplanted heart. Evidence for adenosine as a messenger in angina pectoris

In this pilot study some cardiac effects of exogenous adenosine on the denervated heart were studied in a patient with transplanted heart since 3 years. He was instrumented with catheters into the left coronary artery, the coronary sinus and the right ventricle. Adenosine was given in increasing doses intracoronarily, into the aorta at the diaphragmal level and into a peripheral vein. When given into the aorta pain was provoked dose-dependently and not different from a reference group. When given intracoronarily no pain was provoked except at the highest dose when a slight discomfort of the chest was provoked. After intravenous injection no pain was provoked in the chest or in adjacent structures. Coronary sinus flow increased dose-dependently and not different from the reference group. No increased heart rate response occurred after intravenous or intracoronary injections. Extensive degrees of sinus and AV nodal blockade occurred. In conclusion, the results are in keeping with a role for adenosine as a messenger between myocardial ischaemia and angina pectoris and cardiac sympathetic pressure response. The importance of innervation for proper sinus and AV nodal function was also illustrated.

Atrial natriuretic peptide levels during and after acute cardiac tamponade in dogs

The ability of the atrial wall to secrete atrial natriuretic peptide was studied in eight dogs during 2 h of cardiac tamponade and for 2 h after decompression of the pericardium. Cardiac tamponade was induced by instillation of 5% dextrose in water into the pericardial cavity until aortic systolic pressure was reduced by 30% to 35%. Heart rate, cardiac output and atrial, pericardial and aortic pressures were measured at 60 and 120 min of tamponade and at 5, 30, 60, 90 and 120 min after decompression. Blood samples were withdrawn at the same time for the determination of atrial natriuretic peptide and aldosterone levels. Aortic pressure decreased significantly during tamponade and increased after decompression to near control levels. Right and left atrial pressures as well as intrapericardial pressure increased significantly during tamponade and returned to control levels after decompression. The effective transmural pressure, which was reduced during tamponade, was increased significantly at 5 min after decompression. Cardiac output was significantly reduced during tamponade and returned to pretamponade levels after decompression. Over the total experimental period, no significant changes in the levels of atrial natriuretic peptide were observed, whereas aldosterone increased significantly. It is concluded that the increased atrial pressure observed during cardiac tamponade did not stimulate the secretion of atrial natriuretic peptide. Furthermore, atrial distension observed immediately after decompression was not sufficient or of long enough duration to induce measurable increases in atrial natriuretic peptide levels. Finally, the secondary hyperaldosteronism did not activate atrial natriuretic peptide secretion either during cardiac tamponade or after decompression.

Relationship between location of chest pain and site of coronary artery occlusion

Chest pain characteristics and site of coronary artery occlusion were evaluated in 148 patients having single-vessel coronary angioplasty and in 95 patients having double-vessel angioplasty. The locations of chest pain included substernal and left precordium, right precordium and epigastric. The possible sites of pain radiation were limited to neck/jaw, left arm, right arm, and interscapular. The patient described whether or not the pain was typical of previous angina, and the presence of ST segment deviation was noted to be certain that ischemia was present. The analysis showed that the occluded artery could not be reliably identified. However, it was possible to say which artery was most likely not diseased. Patients presenting with substernal or left chest pain with radiation to the left arm had a less than 10% chance of having right coronary artery disease. A patient presenting with epigastric pain radiating to the neck or jaw had a less than 13% chance of having left anterior descending disease. It is concluded that in patients with single- and double-vessel coronary disease, there is some relationship between chest pain pattern and disease location.

The effect of coronary artery occlusion on the cardiovascular response to an aversive stress

The cardiovascular response to a controlled aversive stress was investigated both before and during acute myocardial ischemia. Classical aversive conditioning (a 30-s tone reinforced with a 1-s shock) served as the model of stress while anterior wall myocardial ischemia was induced by the occlusion (hydraulic occluder) of the left anterior descending coronary artery. The conditional response consisted of significant increases (P less than 0.01) in mean arterial pressure (AP, 13.8 +/- 1.9 mm Hg, 14.3%), left ventricular (LV) dP/dtmax (1300 +/- 324 mm Hg/s, 34.7%) and heart rate (HR, 44 +/- 4 beats/min, 46.8%). Mean coronary vascular resistance significantly (P less than 0.01) increased first (CVR, 0.52 +/- 0.18 mm Hg/ml/min, 17.2%), then decreased (0.77 +/- 0.14 mm Hg/ml/min, 25.5%). In contrast, during acute myocardial ischemia both the HR and d(LVP)/dtmax conditional response were significantly reduced (P less than 0.01) by 58 and 54%, respectively (HR, 20.7 +/- 3.8 beats/min, d(LVP)/dt, 756 +/- 226 mm Hg/s). In addition, the initial CVR increase was virtually eliminated (0.13 +/- 0.10 mm Hg/ml/min, 74.0% reduction) while the CVR decrease was significantly reduced (P less than 0.01) by 48% (0.40 +/- 0.15 mm Hg/ml/min) during the coronary occlusion. The mean AP response, however, was not affected by myocardial ischemia. The pre-conditional stimulus cardiovascular variables were similarly unaffected by the coronary artery occlusion. Thus, coronary artery occlusion attenuated both the coronary and cardiac response elicited by an aversive stress. The mechanism mediating this inhibition of the conditional response remains to be determined but may involve the activation of vagal depressor reflexes during the acute ischemia.

Variability of chest pain in suspected acute myocardial infarction according to subjective assessment and requirement of narcotic analgesics

In 653 patients with suspected acute myocardial infarction the course of pain according to subjective assessment and morphine requirement is described. Patients were asked to score pain from 0-10 until a pain-free interval of 12 hours appeared. Different categories of patients constructed from clinical aspects were compared. Although the variability between groups was fairly small, subgroups were found in which the initial intensity of pain was more marked and the duration of pain was longer. Thus patients with larger infarcts according to maximum serum enzyme activity and patients with Q-wave infarction had more severe pain initially and also a longer duration and a higher morphine requirement compared with patients with a lower serum enzyme activity or a non-Q-wave infarction. Other groups with a more severe course of chest pain were those with more intensive pain at home, electrocardiographic signs of acute myocardial infarction on admission to hospital, and finally those with a high systolic blood pressure or a high rate-pressure product on admission to the Coronary Care Unit. We thus conclude that there is a variability of chest pain in suspected acute myocardial infarction and that there are defined groups of patients in which a more severe course of chest pain could be expected.

Chest pain in acute myocardial infarction: a descriptive study according to subjective assessment and morphine requirement

In 722 patients with suspected acute myocardial infarction (MI) we have tried to describe the course of chest pain according to their own assessment and morphine requirement. Patients were asked to score pain from 0-10 every second hour after arrival in the coronary care unit (CCU) and also to score their maximal pain at home. A very high intensity of chest pain was observed at home (mean score 7.1). At arrival in the CCU the mean pain score already had declined to 1.8, although 51% still had chest pain. Pain score declined successively during the first 12 hours in the CCU. At 24 hours after arrival, 20% still had some chest discomfort. In one quarter of the series a score of more than 0 was observed later than 24 hours after arrival in CCU. Patients developing definite MI had, as expected, a longer duration of pain and a much higher requirement of morphine compared with those with no MI. The difference between MI and no MI patients regarding subjective assessment of the initial intensity of pain at home and in hospital was, however, surprisingly low.

Role of reflex sympathetic withdrawal in the hemodynamic response to an increased inotropic state in patients with severe heart failure

Newer positive inotropic agents used in the treatment of severe heart failure not only increase cardiac contractility, but also cause peripheral vasodilation. It is not known to what extent this vasodilation is due to a direct peripheral action of the drug, as opposed to reflex withdrawal of sympathetic tone secondary to an augmented inotropic state. In 16 patients with severe heart failure, a 48 hour intravenous infusion of milrinone, a positive inotropic vasodilator drug, resulted in an increase in stroke volume index from 26 +/- 2 to 34 +/- 3 ml/m2 (p less than 0.001), a reduction in forearm vascular resistance measured by venous plethysmography from 43 +/- 5 to 27 +/- 3 U (p less than 0.003) and an increase in forearm venous capacitance from 2.1 +/- 0.2 to 2.9 +/- 0.2 ml/100 ml (p less than 0.001). To determine whether a withdrawal of sympathetic tone contributed to this vasodilation, milrinone was infused directly into the left main coronary artery in eight of the patients, thereby eliminating any direct vascular effects of the drug. Intracoronary milrinone (50 micrograms/min) caused an increase in peak positive first derivative of pressure (658 +/- 49 to 784 +/- 68 mm Hg/s; p less than 0.01) and stroke volume index (20 +/- 2 to 25 +/- 3 ml/m2; p less than 0.0001), which was associated with a reduction in plasma norepinephrine from 540 +/- 101 to 423 +/- 90 pg/ml (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial pressure and secretion of atrial natriuretic factor into the human central circulation

Atrial natriuretic factor, a peptide found in mammalian cardiac atria, has natriuretic and vasodilatory properties that may be important in the regulation of intravascular volume. To study factors related to its release in human subjects, intracardiac pressures and plasma atrial natriuretic factor concentrations in the central circulation were measured in 34 patients with a variety of cardiovascular disorders. Plasma atrial natriuretic factor concentration increased from the inferior vena cava to the right atrium (76 +/- 24 to 162 +/- 37 pg/ml, p less than 0.001) and from the vena cava to the aorta (76 +/- 24 to 177 +/- 46 pg/ml, p less than 0.001). Mean right atrial pressure was positively correlated with atrial natriuretic factor concentration in the pulmonary artery (r = 0.58, p less than 0.001), and mean pulmonary capillary wedge pressure was positively correlated with concentration in the aorta (r = 0.64, p less than 0.001). In six patients whose atrial natriuretic factor concentrations were measured at two different levels of atrial pressure, increased atrial pressure was accompanied by increased atrial natriuretic factor concentration in the pulmonary artery (p less than 0.01) and aorta (p less than 0.01). Atrial natriuretic factor levels measured in fresh myocardium from a patient undergoing cardiac transplantation showed tissue concentrations in the atria 500-fold higher than tissue concentrations in the ventricles. These data document that atrial natriuretic factor is found in human atrial myocardium and suggest that it may be released in response to increased atrial pressure. Such a secretory release mechanism is consistent with the hypothesis that atrial natriuretic factor plays a role in the regulation of circulatory volume.