Electron microscopic study of the innervation of the heart conduction system in rats]

A systemic quantitative electron microscopic analysis on innervation of the sinus node, the atrioventricular node, the bundle of His and its pedicles within the interventricular septum has been performed in intact hearts of mature rats. The data have been obtained on the size of nonmyelinated and myelinated nerve fibres, efferent and afferent terminals within different parts of the cardiac conductive system, their interconnection with specialized cardiomyocytes have been described. Application of certain methods for electron microscopic investigation on the innervation of mammalian cardiac conductive system has been discussed.     

The development of the conduction system in the mouse embryo heart: IV. Differentiation of the atrioventricular conduction system

The development of the atrioventricular conduction system in the mouse heart has been studied by light and electron microscopy from the time of the completion of ventricular septation to fetal stage II, 13–16 days postcoitum. At the beginning of this period the already established atrioventricular node (AVN) enlarges rapidly into the dorsal AV cushion from the primitive AV tract, reaching almost its full fetal size when septation is complete. The development of the atrionodal interconnections is a slow and complex process. The dorsal atrial myocardium develops on both sides of the node, establishing a muscular overlay over its proximal aspect, and also incorporating the former AV tract. At this time also, the developing muscular interatrial septum grows downward to establish contact with the node, the sinus venosus, and the myocardium of the right and left atrial walls. The distally proceeding differentiation of the ab initio continuous conduction pathway along the AVN, His bundle, and bundle branches demonstrates a progressive and sequential development of high cellular glycogen content. Progressive isolation of the atrioventricular conduction system leading to (still incomplete) insulation by connective tissue, has been observed.     

Blood supply and the atrioventricular conduction system of the dog heart

In 30 experiments in order to specify the blood supply and conducting system in the dog heart, coronal arteries were injected with a contrasting mass that was followed by roentgenography and preparation of the coronal arteries. The topography and blood supply of the atrioventricular conducting system with application of prevital blood supply, and the left coronal artery is the main source of blood supply for all the parts of the cardiac atrioventricular conducting system.     

The development of the early atrioventricular conduction system in the embryonic heart

Recent electrophysiological evidence indicates that periodic spontaneous depolarizations occur in the primordial heart of the bird (and presumably mammal) even before the myocardial cells can contract, and these are initiated in the primordial sinoatrial region. As contractions are generated, these then establish a peristaltic wave. From that time on, during ontogenesis, the contractile sequence follows a regular pattern of development. As chambers form they contract sequentially in the direction of blood flow, even though, in the twisted configuration, myocardial continuities suggest the possibility of short-circuiting the electrical conduction pathways from atrium to bulbus. This implies that, even at these early stages, the electrical properties of the myocardium are not isotropic, and that specialized conduction pathways must exist. To the present time, electrophysiological techniques have limited the direct evidence that can be obtained on these delicate electrically specialized pathways. However, microscopical techniques have permitted studies on the morphological development of the tissue and of the cells in the various regions of the myocardium. The present paper traces the development of cell morphology in these regions, including the development of structural nodes and proximal ventricular fibre pathways, and from these observations, the manner in which the electrical conduction pathways are believed to develop is suggested.     

Influence of cimetidine on hypoglycemia-induced GH secretion]

Dopaminergic drugs inhibit prolactin and stimulate GH secretion. On the contrary antidopaminergic drugs stimulate prolactin and decrease hypoglycemia-induced GH secretion. According to the hypothesis that Cimetidine, an H2-receptor antagonist, decreases hypothalamic dopamine secretion, it was evaluated GH response to hypoglycemia after this drug. It was demonstrated that Cimetidine decreases hypoglycemia-induced GH secretion.     

The capacity for reactive DNA synthesis of the myocytes in the heart conduction system in experimental and clinical myocardial pathology]

The DNA synthesis has been studied in the conductive system (CS) myocytes, compared to that in atrial and ventricular myocytes: 1) in the left ventricular myocardial infarction induced in two- and three-week-old and adult rats, 2) after isoproterenol injections to adult rats and mice, and 3) in the hypertrophied human heart. The extent of DNA synthesis reactivation was evaluated by the cumulative labeling indices in experiments with multiple 3HTdR injections to rats and mice. In the human cardiac myocyte nuclei, the DNA content was determined by the Feulgen-cytophotometry. The difference between the control and experimental mean values of the labeling indices for CS myocyte nuclei was statistically significant only for atrioventricular part of the CS in the infarcted hearts of adult rats. In the human heart CS the ability of myocytes to polyploidization varies from one cell type to another, the lowest being in nodal cells.     

The development of the conduction system in the mouse embryo heart: I. The first embryonic A-V conduction pathway

In the 8-, 9-, and 10-day-old mouse embryos, the primitive atria are interconnected with the ventricles via the atrioventricular (A-V) canal. Due to the twisting process of the tubular heart, the wall of the A-V canal establishes continuity not only with the left ventricle but also with the bulbus and truncus arteriosus. At this stage of heart development, the A-V node and bundle have not yet appeared, and, thus, the atrial impulse must be conveyed to the ventricle by the muscle tissue of the wall of the A-V canal, in which two muscle cell layers have been observed. The inner layer extends deep into the left ventricular cavity and is interconnected with both the trabecular system and the ventricular (IV) septum, which begins to develop on the tenth day. In the inner dorsal wall of the A-V canal, the cells are large (～ 20 μm in diameter) and show a strong PAS reaction. It is likely that these large glycogen-rich cells from which the A-V node primordium develops on the eleventh day play the main role in the A-V impulse conduction. The muscle cells at the ventrolateral walls of the canal are small and form a loose spongy myocardium into which the connective tissue cells begin to penetrate on the tenth day, ultimately to form the annulus fibrosus. At the same time, the outer cell layer of the dorsal wall begins to deteriorate; the cells show vacuolar degeneration, myolysis, and shrinkage necrosis. This process appears to represent a programmed cell death, as was described in the bird heart (Pexieder, 1975). On the basis of morphological data, the sequence of atrioventricular activation before the appearance of the A-V node and bundle is discussed.     

Laser endoscopic destruction of the atrioventricular junction of the heart conduction system in an experiment

Feasibility and degree of local AV junction destruction were studied prior to the induction of complete transversal block on the model of 18 isolated perfused dog hearts, using endoscopic laser device, employing cardiofibroscope and laser Ne: YAG. Morphological pattern in the destruction zone is presented. The technique and device can be used for transvenous AV junction destruction.