Intrinsic cardiac rate regulation in the anaesthetized rabbit

Intrinsic cardiac regulation, the direct effect of changes in right atrial pressure on heart rate, was examined in rabbits under chloralose/urethane anaesthesia. Autonomic influences on the cardiac pacemaker were eliminated by cervical vagotomy and intravenous propranolol. Right atrial transmural pressure was monitored as the difference between right atrial and pleural pressures. Blood volume expansion (5–15%) increased right atrial transmural pressure and heart rate and produced a sinus arrhythmia associated with respiration-linked fluctuations in right atrial transmural pressure. The gain of intrinsic cardiac rate regulation was calculated as 0.96 ± 0.24 beats min^-1 mmHg^-1 at a heart rate of 218 ± 6 beats min^-1 (values as the mean± SEM, n= 12). When heart rate was reduced by electrical stimulation of the peripheral end of the right vagus nerve, gain increased to 2.25± 0.57* and 4.61 ± 1.6* beats min^-1 mmHg^-1 at heart rates of 180 ± 4 and 130 ± 4 beats min^-1, respectively (n= 6 and n= 10; *P < 0.05 compared with pre-stimulation values). During vagally-induced bradycardia, rapid infusion of blood into the left superior vena cava produced a brief marked cardiac acceleration. We conclude that right atrial pressure has a small direct influence on heart rate, and this is enhanced by background cardiac parasympathetic stimulation.     

Anatomical study of the neural ganglionated plexus in the canine right atrium: Implications for selective denervation and electrophysiology of the sinoatrial node in dog

The aim of the present study was to elucidate the topography and architecture of the intrinsic neural plexus (INP) in the canine right atrium because of its importance for selective denervation of the sinoatrial node (SAN). The morphology of the intrinsic INP was revealed by a histochemical method for acetylcholinesterase in whole hearts of 36 mongrel dogs and examined by stereoscopic, contact, and electron microscopes. At the hilum of the heart, nerves forming a right atrial INP were detected in five sites adjacent to the right superior pulmonary veins and superior vena cava (SVC). Nerves entered the epicardium and formed a INP, the ganglia of which, as a wide ganglionated field, were continuously distributed on the sides of the root of the SVC (RSVC). The epicardiac ganglia located on the RSVC were differentially involved in the innervation of the sinoatrial node, as revealed by epicardiac nerves emanating from its lower ganglia that proceed also into the atrial walls and right auricle. The INP on the RSVC (INP‐RSVC) varied from animal to animal and in relation to the age of the animal. The INP‐RSVC of juvenile dogs contained more small ganglia than that of adult animals. Generally, the canine INP‐RSVC included 434 ± 29 small, 17 ± 4 medium‐sized, and 3 ± 1 large epicardiac ganglia that contained an estimated 44,700, 6,400, and 2,800 neurons, respectively. Therefore, the canine right atrium, including the SAN, may be innervated by more than 54,000 intracardiac neurons residing mostly in the INP‐RSVC. In conclusion, the present study indicates that epicardiac ganglia that project to the SA‐node are distributed more widely and are more abundant than was previously thought. Therefore, both selective and total denervation of the canine SAN should involve the whole region of the RSVC containing the INP‐RSVC. Anat Rec 255:271–294, 1999. © 1999 Wiley‐Liss, Inc.     

Chiari anomalies in the human right atrium

Chiari anomalies in the human right atrium ostensibly are encountered rarely. There is only sporadic mention in the literature of these fenestrated, net-like valves of the inferior vena cava, coronary sinus, or various strands connecting these with other right atrial structures. The effects of such structural anomalies on heart function are unknown. We report here gross observations of the right atrial net from among 213 cadavers, 38 autopsied, and 11 fetal hearts. Histological and ultrastructural examination of inferior vena cava and coronary sinus valves demonstrated that only the anomalous coronary sinus valves contained cardiac muscle. Chiari anomalies typically have referred to perforations or tissue strands related to the inferior vena cava valve and possibly the coronary sinus valve. The anomaly commonly is cited as occurring in 2% of individuals, although there has been no study to support this. We observed Chiari malformations in 13.6% of the 213 cadaver hearts, and 10.5% of the autopsied hearts examined. Of these malformations, the coronary sinus valve was fenestrated most frequently. We propose the term "right atrial net" for "Chiari net," for anomalies involving valves of the inferior vena cava and coronary sinus, and strands within the right atrium connecting these valves with the crista terminalis, right atrial wall, or interatrial septum.     

Experimental analysis of macroreentry formation in the rabbit right atrium

Kaunas Medical Academy. (Presented by Academician of the Academy of Medical Sciences of the USSR J. J. Bredikis.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 111, No. 4, pp. 355–359, April, 1991.     

Atrial plasma ANP and NH2-terminal proANP during right atrial pressure increase in humans

To compare plasma NT-proANP, a stable and biologically inactive N-terminal portion of ANP prohormone, with the known plasma ANP response to increased right atrial pressure a Swan–Ganz catheter was inserted into the right atrium of five normal healthy male volunteers. The elevation of right atrial pressure was produced by a head-down tilt after a hypertonic saline infusion. Blood samples were drawn from the lumen of the right atrium. After 5 min of starting the tilt the right atrial pressure had increased from 7.0±1.0 to 11.6±0.9 mmHg (P<0.05) and then began to normalize in spite of the constant tilt. Atrial plasma ANP increased in relation to the pressure increase and peaked at 15 min after the start of the tilt. The change was from 27.9±6.5 to 53.9±9.7 pmol L^-1 (P<0.05). Atrial plasma NT-proANP increased significantly from 357±91.2 to 529.1±116.0 pmol L^-1 (P<0.05) at 10 min and remained high throughout the experiment. The molar ratio of NT-proANP to ANP varied in atrial plasma from 9.5±1.2 to 13.9±2.7 showing that the plasma clearance of ANP from plasma was much higher than that of NT-proANP.     

Effect of increased α-adrenergic activity on the blood pressure/cardiac output relationship in dogs

The relationship between mean aortic blood pressure (MAP) and cardiac output (CO) was examined in anaesthetized, open-chest dogs during variations in pre-load with and without α-adrenergic stimulation with phenylephrine. When phenylephrine increased MAP to 200 mmHg, CO fell greatly and could not be increased by volume expansion. Left ventricular ultrasonic measurements and pressure recordings showed that the Frank-Starling mechanism was maximally activated. During vena cava obstruction CO and MAP fell proportionally. At a lower infusion rate of phenylephrine, MAP increased to 160 mmHg without a great reduction of CO. As in control experiments without phenylephrine infusion, CO could be increased by dextran/saline infusion and lowered about 20% below control by vena cava obstruction with no significant change in MAP; by further caval obstruction CO and MAP fell in proportion. Phenylephrine did not alter the relationship between aortic baroreceptor activity and MAP. The same MAP/CO relationships were obtained before and after bilateral vagotomy and nephrectomy. Caval obstruction and pacing tachycardia resulted in similar MAP/CO relationships despite different effects on left ventricular end-diastolic pressure. Thus, phenylephrine infusion may raise MAP to 200 mmHg but no cardiac reserve is left. During reduction of CO by caval obstruction, peripheral vascular resistance remains constant despite varying baroreceptor activity. At the lower infusion rate of phenylephrine, raising MAP to 160 mmHg, peripheral vascular resistance is constant at low CO, but at high CO the vasoconstrictive effect of phenylephrine is counteracted by a vasodilatory mechanism which seems to be flow-dependent.     

右心房孤立性转移性肝细胞癌1例报告及文献复习

目的：探讨右心房孤立性转移性肝细胞癌的临床病理特征。方法：分析1例右心房孤立性移性肝细胞癌的临床表现、组织学特征和免疫组织化学（免疫组化）结果,结合文献分析讨论。结果：患者男性,47岁;活动后胸闷,伴双下肢水肿;组织学显示瘤细胞多边形,呈巢状、片状或条索状排列,可见片状坏死;免疫组化：肝细胞特异性抗原-1（Hepatocyte specific antigen-1,Hep-1）、甲胎蛋白（Alpha fetoprotein,AFP）、细胞角蛋白18（Cytokeratin18,CK18）和癌胚抗原（Carcinoembryonic antigen,CE A）阳性,细胞增殖核抗原（nuclcar-associated antigen Ki-67,Ki-67）阳性标记指数为60%,CD34血窦阳性。结论：右心房孤立性肝细胞癌转移比较罕见,早期症状不明显不易引起注意,依据临床和病理组织学特点,结合免疫组化染色可明确诊断。     

Independence of changes in right atrial pressure and central venous pressure

Dynamics of changes in right-atrial pressure and venous pressure measured in the inferior and superior vena cava at their orifices (central venous pressure) after bolus injection of 20 ml physiological saline or epinephrine (5.0 g/kg) was studied in acute experiments on cats. The initial pressure in the right atrium was equal to that in caval veins. Pressor stimuli either increased or decreased the right atrial pressure, but always increased blood pressure in the caval veins. Moreover, right atrial pressure returned to the initial level more rapidly compared to that in caval veins. Our results suggest that the dynamics of the right-atrial pressure does not reflect the shifts in the central venous pressure.     

Effect of amphetamine and gutimin on adaptive changes in blood pressure during skeletal muscular contraction

The effect of amphetamine and gutimin on the arterial pressure reflex to skeletal muscular contraction in response to stimulation of spinal ventral roots was investigated in acute experiments on decerebrate, unanesthetized cats. Doses of the drugs increasing locomotor activity and physical working capacity were used. Amphetamine in a dose of 0.1 mg/kg raised the systemic arterial pressure and the amplitude of the pressor reflexes. If the dose of amphetamine was increased to 1–11 mg/kg the pressor reflex was inhibited and the arterial pressure began to fall. Gutimin (5–50 mg/kg) raised the arterial pressure but did not affect the amplitude of the pressor response to skeletal muscular contraction.Department of Pharmacology, I. P. Pavlov First Leningrad Medical Institute. Department of Physical Education, Leningrad Shipbuilding Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR S. V. Anichkov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 80, No. 12, pp. 41–44, December, 1975.     

Length-dependent changes of pacemaker frequency in the isolated rabbit sinoatrial node

To correlate changes in pacemaker frequency with those of length and tension in mammalian atrial tissues, a strip of the sinoatrial (SA) nodal tissue (about 10 mm in length and 4 mm in width) isolated from the rabbit heart was subjected to constant-length and constant-load stretches, and the relation between the resulting pacemaker frequency changes and the segmental length changes of the preparation was examined by means of cinematographic recording of the preparation with carbon markers on its surface. The amount of stretch-induced length changes was larger in the perinodal tissue segments than in the SA nodal segments, indicating that the nodal area is less extensible than the perinodal area. The time course of stretch-induced length changes of one nodal segment (closer to the inferior vena cava) was found to roughly parallel that of pacemaker frequency changes, suggesting that the pacemaker frequency is primarily dependent on the length but not on the tension of the SA nodal area.     

Effect of nonachlazine on the frequency and amplitude of contractions of the isolated atrium

The effect of the new antianginal drug nonachlazine on the frequency and amplitude of contractions of the isolated atrium of guinea pigs and albino rats was studied. In experiments on the isolated atrium nonachlazine as a rule depresses these parmeters. This effect of the drug on the isolated atrium is evidently due to the direct effect of nonachlazine on the myocardium and on the conducting system of the heart. No species differences were found in the character of the action of nonachlazine.Laboratory of Pharmacology of the Cardiovascular System, Institute of Pharmacology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR, V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 83, No. 3, pp. 298–300, March, 1977.     

Effect of bombesin on thermoregulation of the rabbit

Injections of bombesin (BOM, 125, 250 and 500 ng) into the preoptic/anterior hypothalamus caused dose-related decreases of threshold temperatures for metabolic cold defence, cutaneous vasomotor tone and respiratory rate, combined with a reduced sensitivity of these thermoregulatory effectors in response to core temperature changes induced at thermoneutral or warm ambient conditions. Intracisternal (i.c.) injections of BOM (250 ng) produced qualitatively identical thermoregulatory effector changes in response to core temperature changes. Injections of BOM into the posterior hypothalamus did not affect body temperature control. Increased locomotor behavior, licking and grooming was elicited, however, from all injection sites. The results explain the prevailing hypothermic effect of BOM as the consequence of the concerted decrease in threshold temperatures and gains of all autonomic thermo-regulatory effectors and suggest the activation of warm inputs, relative to cold inputs, at the hypothalamic level as the underlying mechanism. Direct or indirect inhibition of the intrinsic hypothalamic system involving thyrotropin-releasing hormone (TRH) and consequent deactivation of central noradrenergic pathways known to generate the entire autonomic pattern of cold defence might be involved in the neuro-humoral changes resulting in hypothermic effects of centrally applicated BOM.     

Effect of electrical stimulation of right stellate ganglion on cardiac function in rats during postnatal ontogeny

In all examined age groups of rats, the threshold amplitude of stellate ganglion stimulation is higher for the positive chronotropic effect than for the inotropic effect. The stimulation produced a more pronounced effect on stroke volume than on heart rate.     

Structural characteristics of cardiomyocytes in the right atrium of NISAG rats

Electron microscopy and stereomorphometric analysis of hypertrophic cardiomyocytes in the right atrium of NISAG rats revealed signs of activation of biosynthetic processes: increased relative volume of euchromatin (compared to Wistar rats), high density of nuclear pores, presence of large numerous Golgi complexes, and well-developed endoplasmic reticulum. The numerical density of secretory granules in the cytoplasm of cardiomyocytes in NISAG rats significantly surpassed that in Wistar rats. However, these granules in NISAG rats were smaller than in Wistar rats. The presence of numerous secretory granules and increased ratio of forming and dissolving structures suggest that this pool is characterized by high turnover rate,i.e., intensive synthesis and rapid elimination (consumption) of natriuretic peptide. Hypertrophy and hyperactivity of endocrine function in atrial cardiomyocytes of NISAG rats can be considered as a compensatory reaction to hypertension. Translated fromByulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 138, No. 7, pp. 4–8, July, 2004     

Morphological pattern of intrinsic nerve plexus distributed on the rabbit heart and interatrial septum

Although the rabbit is routinely used as the animal model of choice to investigate cardiac electrophysiology, the neuroanatomy of the rabbit heart is not well documented. The aim of this study was to examine the topography of the intrinsic nerve plexus located on the rabbit heart surface and interatrial septum stained histochemically for acetylcholinesterase using pressure‐distended whole hearts and whole‐mount preparations from 33 Californian rabbits. Mediastinal cardiac nerves entered the venous part of the heart along the root of the right cranial vein (superior caval vein) and at the bifurcation of the pulmonary trunk. The accessing nerves of the venous part of the heart passed into the nerve plexus of heart hilum at the heart base. Nerves approaching the heart extended epicardially and innervated the atria, interatrial septum and ventricles by five nerve subplexuses, i.e. left and middle dorsal, dorsal right atrial, ventral right and left atrial subplexuses. Numerous nerves accessed the arterial part of the arterial part of the heart hilum between the aorta and pulmonary trunk, and distributed onto ventricles by the left and right coronary subplexuses. Clusters of intrinsic cardiac neurons were concentrated at the heart base at the roots of pulmonary veins with some positioned on the infundibulum. The mean number of intrinsic neurons in the rabbit heart is not significantly affected by aging: 2200 ± 262 (range 1517–2788; aged) vs. 2118 ± 108 (range 1513–2822; juvenile). In conclusion, despite anatomic differences in the distribution of intrinsic cardiac neurons and the presence of well‐developed nerve plexus within the heart hilum, the topography of all seven subplexuses of the intrinsic nerve plexus in rabbit heart corresponds rather well to other mammalian species, including humans.     

In Vitro Effect of Acetylcholine on Function of Sinoatrial Node in Rat Heart

Electrophysiological parameters of true pacemakers in the sinoatrial node of rat heart were recorded intracellularly using glass microelectrodes. In 11 of 13 experiments acetylcholine in increasing doses did not induce migration of the dominant pacemaker region, while in two cases its minor migration upstream the sinus node artery was observed.     

Chronic increases in transmural pressure reduce NO‐mediated dilations in isolated resistance arteries of the hamster

It is unclear whether the impairment of NO‐mediated dilation in hypertension is the cause or the consequence of high blood pressure. We therefore studied in isolated resistance arteries whether elevated transmural pressure affects NO‐mediated dilation. Arteries (n=5–7) were perfused at hydrostatic pressures of either 45, 120 or 160 mmHg for 48 h. Subsequently, diameter and calcium responses (fura 2) were studied at a transmural pressure of 45 mmHg. Pre‐exposure to 120 and 160 mmHg reduced resting diameters and minimal diameters after stimulation with noradrenaline and significantly increased corresponding intracellular free calcium levels in vascular smooth muscle. Moreover, the NO‐mediated dilation in response to acetylcholine was significantly reduced although the increase in endothelial calcium was not altered. Dilations induced by the NO donor SNP were not affected. It is concluded that chronically elevated pressure per se impairs endothelial NO production by a mechanism distal to receptor‐dependent calcium increases.     

Influence of Changes in Intrathoracic and Central Venous Pressure on Cardiac Filling Dynamics

Changes in the ratio between intrathoracic and central venous pressure were studied in narcotized cats under conditions of constant positive or negative pressure ventilation. Transformation of elastic characteristics in the respiratory system caused by changes in intrathoracic pressure led to inversion of the ratio between transpulmonary intrathoracic and central venous pressure determining right atrial filling pressure.     

Dependence of blood pressure changes in cats during acute hypoxic hypoxia on the type of carotid sinus reflex

The type and degree of blood pressure changes in cats were studied in acute experiments under conditions of acute hypoxic hypoxia (40% decrease in oxygen partial pressure). During hypoxia, blood pressure increased in cats with pressor type of the carotid sinus reflex and decreased in animals with depressor type of this reflex. Our results indicate that the direction and degree of hypoxic changes in blood pressure in animals coincide with variations in this parameter in response to the carotid sinus reflex. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 142, No. 11, pp. 490–493, November, 2006